Willingness to pay for faecal sludge management services - a scoping review

Willingness to pay for faecal sludge management services - a scoping review | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Willingness to pay for faecal sludge management services - a scoping review Hiroaki Tomoi, Clara MacLeod, Taeko Moriyasu, Sheillah Simiyu, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3265808/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 17 Jan, 2024 Read the published version in Environmental Science & Technology → Version 1 posted You are reading this latest preprint version Abstract Under Sustainable Development Goal 6, a target (6.2) of achieving universal access to safely managed sanitation services was established. For safely managed sanitation, waste must be safely disposed of in situ or transported and treated offsite. The cost and availability of services to ensure safe management of onsite sanitation, such as pit latrines and septic tanks, can be major barriers for poor households. This scoping review aimed to scope the literature on willingness to pay (WTP) for emptying onsite sanitation and identify determinants of WTP and gaps in knowledge. Through searches of six databases, and after de-duplication, we identified 1,846 studies, of which 14 studies were included after review. Within the 14 included studies we identified 26 distinct investigation scenarios that reported WTP and market price. Among them, 77% (20/26 scenarios) reported that the WTP was lower than the market price. Twenty statistically significant determinants of WTP were identified, which we categorised as economic situation, urgency, service characteristics, service accessibility, and knowledge. The principal knowledge gap was WTP for services designed to reduce prices and/or increase WTP by improving supply-side efficiency or using mobile money. Addressing this gap could help address the challenge of achieving safely managed services for all. Environmental Economics onsite sanitation SDG6 sludge removal developing countries operational cost affordability economic analysis willingness to pay Figures Figure 1 SYNOPSIS This is the first scoping review to map existing findings and identify research priorities regarding willingness to pay for sludge emptying services. INTRODUCTION While Sustainable Development Goal (SDG) 6 calls for universal access to water and sanitation by 2030, 3.5 billion people still lacked safely managed sanitation services in 2022. (1) Lack of access to safely managed sanitation services not only degrades the environment and poses considerable public health risks (2), but also has wider societal impacts on economic opportunities, education, gender, and well-being. (3–5) Onsite sanitation facilities, such as pit latrines and septic tanks, are widely used in settings where sewer systems are financially or technically not practical, such as rural settings or low-income urban settings. (6) Faecal sludge management (FSM) comprises five steps: containment (storage), emptying (collection), transport, treatment, and reuse/disposal (7, 8). The WHO/UNICEF Joint Monitoring Programme suggests that safely managed faecal sludge with onsite systems requires excreta to either be safely disposed of onsite or transported and treated offsite. However, in densely populated areas where no additional place for containment or sewer systems is available, transporting and treating the sludge offsite is often the last resort. (9) Therefore, safely maintaining the FSM value chain is essential in achieving SDG6, especially in densely populated settings such as informal urban settlements. FSM services are often provided by the private sector - with or without public oversight and regulation – and the financial costs of sanitation containment and emptying are met by the user, that is the household. (10–12) Unlike containment, where a number of financial interventions have been created to support the latrine installation costs by governments and donor organisations, the operational costs for collection, transportation, treatment and disposal of faecal sludge are often left to the household. (13, 14) However, markets often fail in the provision of safe and affordable services to all, and consequently, financial constraints faced by the household can be a major barrier to ensuring safely managed sanitation services. (9, 15, 16) The enabling environment for FSM is often weak and presents complex political economy challenges. (17) Affordability of sanitation services depends on (i) price, (ii) the household’s spending power and time budget (available time), and (iii) the price or cost of other household needs. (18) To estimate affordability, willingness to pay (WTP), the maximum amount that a consumer is willing to pay for a particular good or service, has been widely reported as a proportion of household income or expenditure. (18, 19) This indicator is common in the water supply and sanitation sector to determine the economic feasibility and sustainability of projects or interventions, rationale for market prices, and policymaking, such as socially equitable subsidies and tariffs. (9, 20, 21) WTP can be divided into stated WTP and revealed WTP. Stated WTP is elicited by asking respondents about their valuation, whereas revealed WTP is estimated by observing actual behaviour in a market. (22) For example, in the water and sanitation sector, stated WTP has generally been estimated through the contingent valuation (CV) method and discrete choice experiments (DCEs). (9, 23) Revealed WTP has been examined through real-money coupon trials, aiming to design improved emptying services or estimate household subsidy requirements to support proper emptying behaviour. (21, 23) CV methods directly ask respondents about their WTP for a hypothetical good or service with several variations: open-ended question; bidding game; payment card; and, single/double-bounded dichotomous choice. (24) DCEs do not directly ask respondents about their WTP but start with presenting two or more hypothetical options (profiles) of a good or a service. These goods or services have slightly different prices and characteristics (attributes), and the respondents choose a preferable one or rank them. (25) To date, two systematic reviews have reported that affordability or cost is one of the main determinants of emptying options.(26, 27) In addition, some studies have surveyed households’ WTP for faecal sludge emptying services. However, to the best of our knowledge, there has been no review to date that synthesises the results of these studies, in particular, approaches and scenarios used to elicit WTP, range of WTP amount, and determinants of WTP. This review therefore aims to map those findings and identify a future research agenda to guide policymakers and practitioners for designing or implementing interventions. Existing evidence is synthesised with a focus on the methods and scopes of studies. The relationship between WTP and market prices is summarised to provide evidence on the significance of financial constraints. We also listed statistically significant ( p < 0.05) determinants of WTP. Finally, a future research agenda is proposed based on study trends to date. MATERIALS AND METHODS The review follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) Checklist and Explanation (see more details in supporting information 6). (28) We also refer to the multi-stage methodological framework provided by previous studies. (29–31) The protocol was pre-registered with the Open Science Framework registry in February 2023. (32) Study aim The aim of this scoping review was to scope the literature on WTP for emptying onsite sanitation facilities and identify determinants of WTP and gaps in knowledge. A scoping review was chosen because of its suitability of mapping existing findings, exploring study gaps in the field, and integrating studies of various research methods. (33) Search strategy Six electronic databases, namely EconLit, PubMed, Scopus, Web of Science, WHO Global Index Medicus and the World Bank Open Knowledge Repository, were searched. Search terms related to FSM and WTP were defined based on review articles about similar topics (Table 1 ). (34–37) Although the search was run in English, non-English papers were also included. Titles and abstracts were translated into English using DeepL Translator (DeepL GmbH, Cologne, Germany), a machine translator, to determine eligibility. In addition, reference lists of included papers were manually screened for the same eligibility criteria below to identify any additional relevant documents. Table 1 Search Terms Component 1: FSM Component 2: WTP f?ecal sludge OR f?ecal waste OR sanitation OR toilet* OR latrine* OR septic tank* OR sanit* facilit* OR non-networked OR onsite treatment OR WASH OR desludg* OR pit empt* OR sludge remov* OR FSM willing* to pay OR willing*-to-pay OR WTP OR economic analysis OR economic evaluation OR cost analysis OR cost evaluation OR contingent valuation OR conjoint analysis OR discrete choice OR auction OR bidding OR Becker-DeGroot-Marschak OR take-it-or-leave-it Eligibility criteria This review includes literature which examines the households’ WTP for faecal sludge emptying services. Only studies reporting primary results were included. Papers that only examine WTP for infrastructure and services that do not relate to emptying services (e.g., WTP for a new pit slab) were excluded. However, sanitation services which integrate several components of FSM value chain, such as emptying (e.g., container-based sanitation), were included. No constraints on publication date or language were set. Peer-reviewed and grey literature was included. Study screening and selection Search results were imported into Rayyan and de-duplicated. (38) Titles and abstracts were independently screened by two authors (HT, CM) against inclusion criteria. Full papers of the remaining articles were sought and screened. Data were independently double-extracted by two reviewers (HT, CM). Results were discussed between screeners at each step, with any discrepancies resolved with co-authors (OC, TM, LB). A set of codes that classify the papers were developed to ensure a transparent screening (Supporting Information Table S1). No methodological restrictions were set. Extracting and charting the data A data extraction table was prepared and trialled (Supporting Information Table S2). Relevant information on study details and WTP was extracted independently by two authors using this table. As there is no published quality assessment tool for WTP studies, we adopted a set of criteria adapted from a technical report for WTP studies in the water supply and sanitation sector published by the Asian Development Bank. (20) We applied five quality assessment criteria: (i) survey design including sample size calculation and bid distribution, (ii) instrument validation via pre-test, focus group discussion or similar, (iii) survey implementation including quality control and data management, (iv) mean WTP elicitation, and (v) ex-post validity assessment on WTP. (20) Since WTP data were obtained from different years and reported in different currencies, the values were adjusted for inflation and then expressed in 2022 US dollars (USD) (39). In brief, we first converted an original value (USD) to local currency using the exchange rate at the time of data collection, and then adjusted the value for inflation from original year to 2022 using the local inflation rate. These steps are necessary since the local inflation rate may not reflect the US inflation rate. Finally, the value was converted again to USD again using the 2022 exchange rate. Regarding Tanzania Shilling, as the exchange rate was not available in the World Bank database, we used data from the Exchange Rates UK website. (39–42) RESULTS Search results A total of 2,390 records were identified through electronic searches of six databases and a further four by manual searching of reference lists yielded in our electronic searches. After removing duplicates, 1,846 records were screened by title and abstract, with 148 records eligible for full-text screening and 14 included in our review. Finally, 14 studies are included in this review. The detailed search results are shown in a PRISMA flowchart (Fig. 1 ). Overview of included studies All 14 included studies were conducted in LMICs: studies were from five countries in Sub-Saharan Africa (Tanzania, Sierra Leone, Rwanda, Kenya, and Ghana), four countries in South-East Asia (Philippines, Myanmar, Bangladesh, and Cambodia), and two countries in Central America (Nicaragua and Haiti) (Table 2 ). Research on household WTP for sludge collection and transport appears to have increased recently, in the last decade, with all included studies published since 2013. Eleven studies were conducted in urban or peri-urban areas and three in rural areas. Reported average monthly incomes per household ranged from USD 115 to 196 (adjusted for local inflation and expressed in 2022 USD) (39). The 14 studies reported WTP for 34 scenarios that spanned pit and septic tank emptying and CBS (Table 3 ) . Methods of the studies Eleven studies employed CV methods, and three employed DCE methods; all included measured and reported WTP (Table 2 ). Among the studies using the CV methods, six studies used open-ended question and six used single- or double-bound dichotomous choice approaches. Two of them combined double-bound dichotomous choice approach and open-ended question by asking two dichotomous questions first and subsequently asking in an open-ended style. Two studies also estimated revealed WTP using real-money voucher trials. These trials involved distributing vouchers offering different levels of discount on desludging fees to households and thereafter estimating the revealed WTP from the number of redemptions, along with stated WTP surveys. (21, 23) The services for which WTP was investigated can be classified into three groups: manual emptying (with/without manual desludging pump), mechanical (vacuum pump) emptying, and container-based sanitation (CBS). Sludge containment facilities used at the study sites include dry or pour-flush latrines connected to pit (lined/unlined, tyre, drum), septic tanks, and container-based facilities (see more details in Supporting Information 5). Regarding payment methods, two studies investigated the WTP scenarios where respondents pay the emptying fee via a water bill, and two studies examined WTP via monthly payment to service providers. (21, 44–46) The other studies did not specify the payment method (Table 2 ). Table 2 Overview of included studies and WTP elicitation methods. Author & Year Study country Setting Study Design Type of WTP Service for which WTP was investigated Payment method Harder et al., 2013 (44) Philippines Urban CV: single-bound dichotomous choice Stated Septic tank emptying Water bill Russel et al., 2015 (15) Haiti Urban CV: single-bound dichotomous choice Stated CBS Not specified Jenkins et al., 2015 (9) Tanzania Urban CV: single-bound dichotomous choice Stated Manual desludging pump (Gulper) Not specified Parikh et al., 2016 (47) Sierra Leone Urban CV open-ended Stated Improved pit emptying Not specified Balasubramanya et al., 2017 (13) Bangladesh Urban CV: double-bound dichotomous choice Stated Pit emptying that transports sludge away Not specified Ross & Pinfold, 2017 (48) Rwanda Urban CV: Bidding game Stated Manual /Mechanical emptying with treatment Not specified Vásquez & Alicea-Planas, 2018 (45) Nicaragua Urban DCE Stated Excreta disposal Water bill World Bank, 2019 (49) Cambodia Rural CV: open-ended questions (Price Sensitivity Measurement) Stated Vacuum truck emptying Not specified Burt et al., 2019 (23) Rwanda Urban DCE Real-money voucher trial Stated & Revealed Vacuum truck/manual emptying with group discount Not specified & volumetric/flat pricing Peletz et al., 2020 (21) Kenya Urban CV: double-bounded dichotomous choice + open-ended question Real-money voucher trial Stated & Revealed Manual (formal), Vacuum truck emptying Not specified & subscription/rent premium Naing et al., 2020 (50) Myanmar Urban CV: open-ended questions Stated Vacuum truck emptying 1 Not specified Harper et al., 2021 (51) Cambodia Rural DCE Stated Improved pit emptying Not specified Delaire et al., 2021 (16) Bangladesh Ghana Kenya Urban & Peri-urban CV: double-bounded dichotomous choice + open-ended question Stated CBS, Vacuum truck, Manual (formal) Not specified Singh et al., 2021 (46) Bangladesh Urban CV: open-ended question Stated Emptying services Monthly payment 1 WTP for additional service fees to request emptying services through a phone call rather than visiting the administrative office. CV- contingent valuation Gap between WTP and market price Heterogeneity in service scenarios amongst the studies is caused by factors such as facility type, the number of households sharing one latrine or frequency of emptying. As these metadata were often lacking or reported in a non-standardised form, it is difficult to compare the WTP itself between the studies. Instead, we compare the WTP for a given service as a proportion of the market price or cost of the service (Table 3 ) . We identified 34 WTP scenarios across the 14 included studies, of which nine scenarios (26%) are on manual emptying services, ten (29%) on mechanical pump or vacuum truck services, four (12%) on CBS, while the rest does not specify an emptying method. None of the studies explicitly investigated WTP for informal emptying services. Among the 26 scenarios that reported both mean (or median) WTP and market price (or cost), 20 scenarios (77%) reported that the mean or median WTP did not reach the market price or cost, and 18 scenarios (69%) reported the WTP was lower than half of the market price. While the WTP for one manual emptying and two mechanical emptying scenarios exceeded the market prices, none of the mean WTP for CBS reached the market prices (16% of the price in Haiti, 22–27% in Kenya, and 66% in Ghana). (15, 16) Therefore, the gap between WTP and market price is an important barrier to households' demand for services. Table 3 WTP amount and the gap between the market price. Mean or median WTP amounts are stated WTP unless otherwise stated as revealed WTP. Author & Year Service for which WTP was investigated Study site Payment method Mean/median WTP (adjusted for inflation & converted into 2022 USD) Ratio of WTP to price or cost (%) Jenkins et al., 2015 Manual emptying using Gulper pump Tanzania Not specified USD 31 /300L (median) 153% (median) Ross & Pinfold, 2017 Manual emptying Rwanda Not specified USD 95 (median) NA Peletz et al., 2020 Formal manual emptying (Gasia Poa) Kenya, Kisumu Not specified USD 31 (median) USD 35 (mean) 25–43% (median) Peletz et al., 2020 Formal manual emptying (Gasia Poa) Kenya, Kisumu Subscription /rent premium Ranging from 44% of households willing to pay USD 3 to 12% of willing to pay USD 7 per month NA Delaire et al., 2021 Formal manual emptying using long-handled bucket Kenya, Kisumu Not specified USD 29 (median) USD 34 (mean) 27% (median) 32% (mean) Delaire et al., 2021 Formal manual emptying using Gulper pump Kenya, Nakuru Not specified USD 44 (median) USD 49 (mean) 31% (median) 35% (mean) Delaire et al., 2021 Formal manual emptying using diesel pump Kenya, Malindi Not specified USD 49 (median) USD 60 (mean) 40% (median) 49% (mean) Delaire et al., 2021 Formal manual emptying using long-handled bucket Ghana Not specified USD 39 (median) USD 54 (mean) 31% (median) 44% (mean) Delaire et al., 2021 Formal manual emptying using long-handled bucket Bangladesh Not specified USD 12 (median) USD 18 (mean) 13% (median) 20% (mean) Ross & Pinfold, 2017 Mechanical emptying with treatment Rwanda Not specified ~ USD 109 (median) fully covered (> 100%) World Bank, 2019 Vacuum truck Cambodia Not specified USD 14–19 39–55% Burt et al., 2019 Vacuum truck Rwanda Not specified USD 88 (revealed WTP) 152% (95% CI: 120–208%, mean) Peletz et al., 2020 Vacuum truck Kenya, Kisumu Subscription /rent premium Ranged from 52% of households willing to pay USD 2 to 6% willing to pay USD 5 per month 33–50% (median) Peletz et al., 2020 Vacuum truck Kenya, Kisumu Not specified USD 21 (median) USD 22 (mean) 33–50% (median) Peletz et al., 2020 Vacuum truck Kenya, Kisumu Not specified USD 15 (mean, revealed WTP) 27–40% (mean) Delaire et al., 2021 Vacuum truck Kenya, Kisumu Not specified USD 20 (median) USD 21 (mean) 34% (median) 36% (mean) Delaire et al., 2021 Vacuum truck Kenya, Nakuru Not specified USD 29(median) USD 32 (mean) 33% (median) 36% (mean) Delaire et al., 2021 Vacuum truck Kenya, Malindi Not specified USD 25 (median) USD 33 (mean) 18% (median) 21% (mean) Delaire et al., 2021 Vacuum truck Ghana Not specified USD 39 (median) USD 38 (mean) 42% (median) 40% (mean) Delaire et al., 2021 Vacuum truck Bangladesh Not specified USD 18 (median) USD 14 (mean) 20% (median) 24% (mean) Russel et al., 2015 CBS Haiti Not specified USD 4.5 /month (mean) 16% Delaire et al., 2021 CBS Kenya Not specified USD 2.0 (median) USD 2.0 (mean) 22% (median, mean) Delaire et al., 2021 CBS Kenya Not specified USD 2.0 (median) USD 2.4 (mean) 23% (median) 27% (mean) Delaire et al., 2021 CBS Ghana Not specified USD 3.9 (median) USD 4.6 (mean) 55% (median) 66% (mean) Harder et al., 2013 Septic tank emptying Philippines Water bill USD 1.8 /month 128% 2 Parikh et al., 2016 Improved pit emptying Sierra Leone Not specified USD 80 (mean) 116% Balasubramanya et al., 2017 Pit emptying that transports sludge away Bangladesh Not specified ~ USD 7.2 47% Vásquez & Alicea-Planas, 2018 Excreta disposal Nicaragua Water bill USD 3.9 /month NA Naing et al., 2020 WTP for additional fee to request vacuum truck emptying through a phone call Myanmar Not specified USD 7–14 (median) 3 NA Harper et al., 2021 Pit emptying that prevents contact with faecal sludge Cambodia Not specified USD 69 NA Harper et al., 2021 Pit emptying that produces fertilizer from faecal sludge Cambodia Not specified USD 29 NA Harper et al., 2021 Pit emptying that reduces foul odor from high to moderate Cambodia Not specified USD 16 NA Harper et al., 2021 Pit emptying that reduces foul odor from moderate to none Cambodia Not specified USD 23 NA Singh et al., 2021 Emptying services Bangladesh Monthly payment 77% said USD 0.9–4.5 /month 107–535% 4 2 Calculated by authors based on the most probable scenario (3 years desludging interval) 3 Due to a lack of data on the inflation rate and currency exchange rate, the original WTP amount (in 2017) is shown here. 4 Calculated by authors based on the most probable scenario (3 years desludging interval and a 1.96 m 3 average pit volume). Quality assessment A quality assessment was conducted for each study using five pre-specified criteria (Supporting Information Table S3). Six out of 14 studies had insufficient sample size or reported no rationales for sample size, and two reported no bias mitigation strategy for starting point bias or price distribution. Regarding survey preparation, five reported no measures to improve validity of the research instruments. For survey implementation, two studies were prone to non-response bias as a large proportion (30% and 42%) of respondents did not answer their WTP (47, 50), two reported no enumerator training or quality control, and six reported nothing about implementation. As for the WTP elicitation phase, five studies did not report econometric models used to elicit mean WTP. After the WTP elicitation, three studies did not assess the validity of the WTP results against income, price levels. One study (Harper et al ) was assessed to be of good quality, while other included studies had one or more points to improve on in the study designs. (51) Moreover, even though Harper et al minimised biases such as by taking efforts of preliminary testing of research instruments and training for enumerators, they reported that the WTP was likely to be overestimated since their DCE may have caused survey fatigue, primacy effect, and hypothetical bias. (51) Determinants of WTP In total, there are 20 statistically significant ( p < 0.05) determinants of WTP amongst the included studies (Table 4 ). In addition to general factors such as education, gender, age and province, the determinants were classified into five groups: economic situation, service characteristics, service accessibility, urgency, and knowledge. The economic situation determinant suggests that those with higher income show higher WTP (income elasticity). (20) Flat fee is a way of pricing in which customers pay a fixed fee for an emptying event regardless of the amount of sludge removed. A study conducted in low-income settlements in Kigali, Rwanda, reported reduced WTP for flat fee pricing because respondents preferred volumetric pricing. (23) The urgency category suggests that those who need to remove sludge immediately or more frequently than those who do not are willing to pay more. Both larger household size and sharing latrines by some households lead to a higher sludge accumulation rate, and more people suffering inconvenience when latrines are out of service. Conversely, longer waiting time from requesting a service until it is provided leads to less WTP. As sharing one latrine with multiple households is common in informal urban settlements, the issue of urgency is closely related to their WTP. (9, 16) The service characteristics category includes the most determinants. Some specific improvements in sludge removal and transport operation are valued (taking away sludge from the latrine to a remote place, preventing odour). Some determinants do not directly benefit customers but benefit emptiers (worker protection, preventing contact with sludge) or society (sludge treatment before disposal, fertilizer production). The service accessibility category includes factors concerning the physical availability of services. Distance from a road is particularly critical in informal urban settlements as narrow roads and congested buildings often prevent vacuum trucks from operating. (9, 47, 48) In contrast, the determinants in the knowledge category, such as awareness or experience about emptying services, can affect the WTP regardless of whether the service is physically available or not in the area. Education levels were both positively and negatively associated with WTP. (9, 21, 51) While higher education seems to increase valuation of sanitation (51), reasons for the negative association with WTP have not been investigated. (9) Table 4 Determinants of WTP for faecal sludge emptying services which were statistically significant (at 5% level) in one or more studies. Category Determinant Economic situation Income/expenditure (wealth) Price (-) Flat fee (-) Urgency Shared latrine Household size Waiting time (-) Service characteristics Branded service that provides workers with protection Smell prevention during the work Sludge taken away to a remote place Sludge treated (removing smells and pathogens) before disposal Contact with sludge prevented Fertilizer production Service accessibility No hygienic emptying method locally available Distance from a road Knowledge Not knowing any hygienic emptying methods Those who had emptied their latrine using the only available option Others Education (+-) Age Gender (male) Province (+-) *(-) the WTP decreases as the determinant increases. (+－) means the determinant can either increase or decrease WTP. DISCUSSION To our knowledge this is the first scoping review of WTP for sludge emptying services and we identified 14 studies meeting out inclusion criteria. We discuss our results in relation to our study aim: to scope the literature on WTP for emptying onsite sanitation facilities and identify determinants of WTP and gaps in knowledge. WTP elicitation methods We found that CV is the most popular approach for eliciting WTP for FSM services. While CV is flexible and applicable to a variety of scenarios, its disadvantage is that respondents’ WTP are subject to a hypothesis bias. (24) Stated WTP is usually overestimated relative to revealed WTP, since the respondents hypothetically state their willingness to pay without actual payment. (24) There is also an argument that the hypothetical bias could be relatively smaller in sanitation services than other more complex services or abstract environmental values because the hypothetical services posed, i.e. improved sludge collection, are typically purchased in markets and/or extensions of what respondents have used before. (20) Nonetheless, emptying services are not free from the bias as Peletz et al. reported that stated WTP was higher compared with revealed. (20) Two included studies which estimated revealed WTP conducted market experiments using real-money vouchers. In the experiments, a short redemption period, which was three months for both, and logistic complexity were reported as a limitation for eliciting WTP. (21, 23) None of the studies used the hedonic pricing method to investigate the WTP for FSM. This method estimates revealed WTP for a certain service or a characteristic using rent or land prices and is commonly applied in the water and sanitation sector. (52–54) The reason why the hedonic pricing was not employed amongst the included studies could be that emptying services are not constantly provided by houseowners or landlords even in the areas where the owners are financially responsible for the provision (e.g., Kenya, Rwanda, Tanzania). Therefore, the rent may not necessarily reflect the provision of emptying services. (9, 48, 55) Payment method Payment methods affect the WTP since their psychological pain, nature of the payment (voluntary or compulsory) and convenience are different. (56, 57) The payment method adopted in the included studies are water bill (two studies) and monthly payment (two studies), and ten studies that did not specify the method are therefore considered as one-time payment in cash. Any sort of taxes or surcharges have not been considered. Some studies noted that if the market price was spread over the emptying interval, the monthly price would be manageable given the household income, compared to one-time payment. (9, 13) Hence, measures that spread payments over time (e.g., water bills, earmarked savings accounts and monthly subscription) and lower one-time payments (e.g., volumetric pricing (pay-as-you-go)) have been proposed. (23, 49, 58) However, a study carried out in low-income areas of Kisumu, Kenya, reported that WTP for subscription of emptying services with monthly payments was not significantly higher than WTP for one-time payment. (21) These findings imply that payment schemes that are based on the affordability of households at the time of emptying would be more favourable to smaller but continuous payment for low-income people, possibly because they have weak guarantee of future income. Determinants of WTP The set of determinants we presented in Table 4 can be applied as a checklist when improving or introducing new emptying services. In so doing, it is worth noting that some determinants groups are interlinked. First, when households are in urgent situation and want to empty their onsite facility immediately, they may use a service that is more quickly accessible, thereby compromising on emptying quality. Therefore, to capture demand, it is important to keep waiting times short. Regarding the relationship between urgency and economic situation, the more people that share a latrine, the lower the cost per person, but the faster sludge accumulates, which results in more frequent emptying. Hence, future research should consider not only the single household’s WTP but also how many households share one latrine when investigating WTP for emptying services. There may however be collective action challenges in shared sanitation situations. (59) Moreover, the category of service characteristics includes determinants that do not directly benefit customers but benefit emptiers or society, such as determinants related to worker protection (Table 4 ). This finding suggests that users could behave altruistically even if they live in poverty. That said, price tends to increase as the service quality increases, and there could be a trade-off between the two in terms of their impact on WTP. A potential determinant that has not yet been explored in WTP studies is the thickness or density of the sludge. A systematic review has revealed that thickness of sludge affects choices of emptying technology because the thickness varies depending on sanitation facilities. (27) In general, sludge is thicker and denser in unlined pit latrines than in septic tanks and lined pits due to lack of flushing water, which makes mechanical emptying ineffective. Additional work, as well as cost, of adding water may be needed. (27) Therefore, thickness of sludge could affect WTP for manual and mechanical emptying. Research gaps To date, researchers seem to have focused mainly on understanding the current demand (WTP) for existing services and comparing it with service supply (prices or costs). (13, 47) On the other hand, they have not fully examined WTP for emerging services which try to reduce prices. For example, our review identified four studies which investigated how small payment approaches (e.g., water bill, volumetric pricing, monthly payment) could affect households’ WTP comparing with one-time cash payment, and only two of them statistically examined the difference in WTP. (21, 23, 44, 46) Therefore, effectiveness of those approaches has not been sufficiently investigated enough. Methods such as group-emptying and scheduled-emptying have recently been proposed to reduce service prices by aggregating the demand of multiple households for efficient operation. (23, 46) However, there are concerns that these methods do not always provide services at the household's preferred timing, which could reduce WTP. None of the studies employed mobile money as a payment method. Although the influence of mobile money payment on WTP is a relatively new research topic, it has been reported that mobile money could increase the WTP due to its convenience and widespread use in certain contexts. (60) Mobile money services are already prevalent in Sub-Saharan Africa and Asia. (61, 62) For instance, in Kenyan informal settlements, the vast majority (97%) of respondents to a recent WTP survey had the local mobile money, M-Pesa. (21) Unlike cash, mobile payment can be easily combined with other information technology such as geographic information system (GIS) or behavioural science techniques such as “nudging”. (58, 63) Limitations First, although there was no restriction on language, the search was conducted in English so literature published in other languages might have been excluded. Secondly, as this review only included studies with methodologies for WTP elicitation, some peer-reviewed and grey literature with WTP data were excluded. In addition, since the included studies used different methods to elicit WTP and investigated scenarios were heterogeneous, the WTP amounts could not be directly compared. As more studies are conducted in the future, it will be possible to compare WTP amounts in similar settings, which could help improve emptying services. Recommendations for future research This is the first scoping review to map existing findings and to identify research priorities regarding WTP for sludge emptying services. Only 14 studies have been conducted in eleven countries. Market prices exceeded WTP in most (77%) cases. with WTP only covering 13%, 16%, and 18% of the prices for manual emptying, vacuum emptying and CBS, respectively in worst cases. This result indicates that households’ demand for emptying services is hindered by financial constraints in low-income settings. Future research needs to investigate how WTP is affected by interventions that attempt to make services more affordable. It is also worth examining how disadvantage of group-emptying and scheduled-emptying, such as waiting time for service delivery, affects their WTP. In areas where mobile money is prevalent, future research can explore the impacts of mobile payment as well as its application in conjunction with other information technologies or marketing technics. To ensure universal access to safe sanitation by 2030, it is essential that affordable services are available for all, enabling users to safely operate and maintain offsite sanitation systems. Effective interventions that enable low-income communities to implement safe FSM need to be implemented by the public and private sector based on robust evidence including this review. ABBREVIATIONS container-based sanitation, CBS; contingent valuation, CV; discrete choice experiment, DCE; faecal sludge management, FSM; low- and middle-income countries, LMICs; United States dollar, USD; willingness to pay, WTP. DECLARATIONS ASSOCIATED CONTENT Supporting Information . The following information is available free of charge. Example search strategy; List of codes used in the screening process; Components of the data extraction sheet; Results of quality assessment; Characteristics of sanitation management behaviour (PDF); Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) Checklist AUTHOR INFORMATION Author Contributions Conceived by HT. The screening and data extracting processes were conducted by HT and CM. Analysis was performed by HT. The first draft of the manuscript was prepared by HT. All authors contributed to subsequent drafts. All authors have given approval to the final version of the manuscript. ORCID Hiroaki Tomoi: 0000-0002-4711-4203, Clara MacLeod: 0000-0001-6952-9103, Taeko Moriyasu: 0000-0002-8201-3061, Sheillah Simiyu: 0000-0003-3069-8967, Ian Ross: 0000-0002-2218-5400, Oliver Cumming: 0000-0002-5074-8709, Laura Braun: 0000-0001-9319-0859 Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This research was funded in whole by the Nagasaki University WISE Programme. REFERENCES Examples of the recommended format for the various reference types can be found at http://pubs.acs.org/page/4authors/index.html. Detailed information on reference style can be found in The ACS Style Guide, available from Oxford Press. UNICEF, WHO. Progress on household drinking water, sanitation and hygiene 2000–2022: special focus on gender. 2023. Wolf J, Johnston RB, Ambelu A, Arnold BF, Bain R, Brauer M, et al. Burden of disease attributable to unsafe drinking water, sanitation, and hygiene in domestic settings: a global analysis for selected adverse health outcomes. 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Compare Live Foreign Currency Exchange Rate & History (accessed July 27th 2023) [Available from: https://www.exchangerates.org.uk/. World Bank. GDP deflator (base year varies by country) (accessed August 11th 2023) [Available from: https://data.worldbank.org/indicator/NY.GDP.DEFL.ZS. World Bank. Official exchange rate (LCU per US$, period average) (accessed August 11th 2023) [Available from: https://data.worldbank.org/indicator/PA.NUS.FCRF. Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ. 2021;372:n71. Harder DS, Sajise AJU, Galing EM. Willingness to pay for sanitation services in Dagupan City, Philippines. Journal of Water Sanitation and Hygiene for Development. 2013;3(2):165-80. Vásquez WF, Alicea-Planas J. Unbundling household preferences for improved sanitation: A choice experiment from an urban settlement in Nicaragua. Journal of Environmental Management. 2018;218:477-85. Singh S, Gupta A, Alamgir M, Brdjanovic D. Exploring Private Sector Engagement for Faecal Sludge Emptying and Transport Business in Khulna, Bangladesh. Int J Environ Res Public Health. 2021;18(5). Parikh P, Da Cunha Forte J, Parkinson J, Boot N. Assessing demand for faecal sludge management (FSM) services in Freetown. Waterlines. 2016;35(4):336-56. Ross I, Pinfold J. Kigali Urban Sanitation Study - Synthesis Report 2017. World Bank. Household pit emptying and reuse practices in rural Cambodia. 2019. Naing W, Harada H, Fujii S, Hmwe CSS. Informal Emptying Business in Mandalay: Its Reasons and Financial Impacts. Environmental Management. 2020;65(1):122-30. Harper J, Bielefeldt A, Javernick-Will A, Dickinson K, Veasna T, Kozole T, et al. Household Preferences for Rural Fecal Sludge Management Services in Cambodia: A Discrete Choice Experiment. Environmental Science and Technology. 2021;55(3):1832-41. Simiyu S, Swilling M, Rheingans R, Cairncross S. Estimating the Cost and Payment for Sanitation in the Informal Settlements of Kisumu, Kenya: A Cross Sectional Study. International Journal of Environmental Research and Public Health. 2017;14(1). Tidwell JB. Users are willing to pay for sanitation, but not as much as they say: Empirical results and methodological comparisons of willingness to pay for peri-urban sanitation in lusaka, zambia using contingent valuation, discrete choice experiments, and hedonic pricing. Journal of Water Sanitation and Hygiene for Development. 2020;10(4):756-67. Choumert J, Kéré NE, Laré-Dondarini AL. A Multi-Level Housing Hedonic Analysis of Water and Sanitation Access. Economics Bulletin. 2016;36(2):1010-37. Simiyu S, Swilling M, Cairncross S. Decision-making on shared sanitation in the informal settlements of Kisumu, Kenya. Int J Environ Health Res. 2017;27(5):377-93. Boden J, Maier E, Wilken R. The effect of credit card versus mobile payment on convenience and consumers’ willingness to pay. Journal of Retailing and Consumer Services. 2020;52:101910. Ivehammar P. The Payment Vehicle Used in CV Studies of Environmental Goods Does Matter. Journal of Agricultural and Resource Economics. 2009;34(3):450-63. Lipscomb M, Schechter L. Subsidies versus mental accounting nudges: Harnessing mobile payment systems to improve sanitation. J Dev Econ. 2018;135:235-54. Capone D, Buxton H, Cumming O, Dreibelbis R, Knee J, Nala R, et al. Impact of an intervention to improve pit latrine emptying practices in low income urban neighborhoods of Maputo, Mozambique. Int J Hyg Environ Health. 2020;226:113480. Boden J, Maier E, Wilken R. The effect of credit card versus mobile payment on convenience and consumers’ willingness to pay. Journal of Retailing and Consumer Services. 2020;52. Konte M, Tetteh GK. Mobile money, traditional financial services and firm productivity in Africa. Small Business Economics. 2022;60(2):745-69. Islam A, Basher SA, Enamul Haque AK. The impact of mobile money on long-term poverty: evidence from Bangladesh. J Soc Econ Dev. 2022;24(2):436-55. Kampala Capital City Authority. Kampala Faecal Sludge Management Improving Faecal Sludge Management for On-site Sanitation. Supplementary Files 1stSubmissionSupportingInformationWTPscopingreview.docx TableOfContent.png Cite Share Download PDF Status: Published Journal Publication published 17 Jan, 2024 Read the published version in Environmental Science & Technology → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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(1) Lack of access to safely managed sanitation services not only degrades the environment and poses considerable public health risks (2), but also has wider societal impacts on economic opportunities, education, gender, and well-being. (3\u0026ndash;5)\u003c/p\u003e \u003cp\u003eOnsite sanitation facilities, such as pit latrines and septic tanks, are widely used in settings where sewer systems are financially or technically not practical, such as rural settings or low-income urban settings. (6) Faecal sludge management (FSM) comprises five steps: containment (storage), emptying (collection), transport, treatment, and reuse/disposal (7, 8). The WHO/UNICEF Joint Monitoring Programme suggests that safely managed faecal sludge with onsite systems requires excreta to either be safely disposed of onsite or transported and treated offsite. However, in densely populated areas where no additional place for containment or sewer systems is available, transporting and treating the sludge offsite is often the last resort. (9) Therefore, safely maintaining the FSM value chain is essential in achieving SDG6, especially in densely populated settings such as informal urban settlements.\u003c/p\u003e \u003cp\u003eFSM services are often provided by the private sector - with or without public oversight and regulation \u0026ndash; and the financial costs of sanitation containment and emptying are met by the user, that is the household. (10\u0026ndash;12) Unlike containment, where a number of financial interventions have been created to support the latrine installation costs by governments and donor organisations, the operational costs for collection, transportation, treatment and disposal of faecal sludge are often left to the household. (13, 14) However, markets often fail in the provision of safe and affordable services to all, and consequently, financial constraints faced by the household can be a major barrier to ensuring safely managed sanitation services. (9, 15, 16) The enabling environment for FSM is often weak and presents complex political economy challenges. (17)\u003c/p\u003e \u003cp\u003eAffordability of sanitation services depends on (i) price, (ii) the household\u0026rsquo;s spending power and time budget (available time), and (iii) the price or cost of other household needs. (18) To estimate affordability, willingness to pay (WTP), the maximum amount that a consumer is willing to pay for a particular good or service, has been widely reported as a proportion of household income or expenditure. (18, 19) This indicator is common in the water supply and sanitation sector to determine the economic feasibility and sustainability of projects or interventions, rationale for market prices, and policymaking, such as socially equitable subsidies and tariffs. (9, 20, 21) WTP can be divided into stated WTP and revealed WTP. Stated WTP is elicited by asking respondents about their valuation, whereas revealed WTP is estimated by observing actual behaviour in a market. (22) For example, in the water and sanitation sector, stated WTP has generally been estimated through the contingent valuation (CV) method and discrete choice experiments (DCEs). (9, 23) Revealed WTP has been examined through real-money coupon trials, aiming to design improved emptying services or estimate household subsidy requirements to support proper emptying behaviour. (21, 23) CV methods directly ask respondents about their WTP for a hypothetical good or service with several variations: open-ended question; bidding game; payment card; and, single/double-bounded dichotomous choice. (24) DCEs do not directly ask respondents about their WTP but start with presenting two or more hypothetical options (profiles) of a good or a service. These goods or services have slightly different prices and characteristics (attributes), and the respondents choose a preferable one or rank them. (25)\u003c/p\u003e \u003cp\u003eTo date, two systematic reviews have reported that affordability or cost is one of the main determinants of emptying options.(26, 27) In addition, some studies have surveyed households\u0026rsquo; WTP for faecal sludge emptying services. However, to the best of our knowledge, there has been no review to date that synthesises the results of these studies, in particular, approaches and scenarios used to elicit WTP, range of WTP amount, and determinants of WTP. This review therefore aims to map those findings and identify a future research agenda to guide policymakers and practitioners for designing or implementing interventions. Existing evidence is synthesised with a focus on the methods and scopes of studies. The relationship between WTP and market prices is summarised to provide evidence on the significance of financial constraints. We also listed statistically significant (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) determinants of WTP. Finally, a future research agenda is proposed based on study trends to date.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cp\u003eThe review follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) Checklist and Explanation (see more details in supporting information 6). (28) We also refer to the multi-stage methodological framework provided by previous studies. (29\u0026ndash;31) The protocol was pre-registered with the Open Science Framework registry in February 2023. (32)\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy aim\u003c/h2\u003e \u003cp\u003eThe aim of this scoping review was to scope the literature on WTP for emptying onsite sanitation facilities and identify determinants of WTP and gaps in knowledge. A scoping review was chosen because of its suitability of mapping existing findings, exploring study gaps in the field, and integrating studies of various research methods. (33)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eSearch strategy\u003c/h2\u003e \u003cp\u003eSix electronic databases, namely EconLit, PubMed, Scopus, Web of Science, WHO Global Index Medicus and the World Bank Open Knowledge Repository, were searched. Search terms related to FSM and WTP were defined based on review articles about similar topics (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). (34\u0026ndash;37) Although the search was run in English, non-English papers were also included. Titles and abstracts were translated into English using DeepL Translator (DeepL GmbH, Cologne, Germany), a machine translator, to determine eligibility. In addition, reference lists of included papers were manually screened for the same eligibility criteria below to identify any additional relevant documents.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSearch Terms\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComponent 1: FSM\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eComponent 2: WTP\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ef?ecal sludge OR f?ecal waste OR sanitation OR toilet* OR latrine* OR septic tank* OR sanit* facilit* OR non-networked OR onsite treatment OR WASH OR desludg* OR pit empt* OR sludge remov* OR FSM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ewilling* to pay OR willing*-to-pay OR WTP OR economic analysis OR economic evaluation OR cost analysis OR cost evaluation OR contingent valuation OR conjoint analysis OR discrete choice OR auction OR bidding OR Becker-DeGroot-Marschak OR take-it-or-leave-it\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eEligibility criteria\u003c/h2\u003e \u003cp\u003eThis review includes literature which examines the households\u0026rsquo; WTP for faecal sludge emptying services. Only studies reporting primary results were included. Papers that only examine WTP for infrastructure and services that do not relate to emptying services (e.g., WTP for a new pit slab) were excluded. However, sanitation services which integrate several components of FSM value chain, such as emptying (e.g., container-based sanitation), were included. No constraints on publication date or language were set. Peer-reviewed and grey literature was included.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eStudy screening and selection\u003c/h2\u003e \u003cp\u003eSearch results were imported into Rayyan and de-duplicated. (38) Titles and abstracts were independently screened by two authors (HT, CM) against inclusion criteria. Full papers of the remaining articles were sought and screened. Data were independently double-extracted by two reviewers (HT, CM). Results were discussed between screeners at each step, with any discrepancies resolved with co-authors (OC, TM, LB). A set of codes that classify the papers were developed to ensure a transparent screening (Supporting Information Table S1). No methodological restrictions were set.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eExtracting and charting the data\u003c/h2\u003e \u003cp\u003eA data extraction table was prepared and trialled (Supporting Information Table S2). Relevant information on study details and WTP was extracted independently by two authors using this table.\u003c/p\u003e \u003cp\u003eAs there is no published quality assessment tool for WTP studies, we adopted a set of criteria adapted from a technical report for WTP studies in the water supply and sanitation sector published by the Asian Development Bank. (20) We applied five quality assessment criteria: (i) survey design including sample size calculation and bid distribution, (ii) instrument validation via pre-test, focus group discussion or similar, (iii) survey implementation including quality control and data management, (iv) mean WTP elicitation, and (v) ex-post validity assessment on WTP. (20)\u003c/p\u003e \u003cp\u003eSince WTP data were obtained from different years and reported in different currencies, the values were adjusted for inflation and then expressed in 2022 US dollars (USD) (39). In brief, we first converted an original value (USD) to local currency using the exchange rate at the time of data collection, and then adjusted the value for inflation from original year to 2022 using the local inflation rate. These steps are necessary since the local inflation rate may not reflect the US inflation rate. Finally, the value was converted again to USD again using the 2022 exchange rate. Regarding Tanzania Shilling, as the exchange rate was not available in the World Bank database, we used data from the Exchange Rates UK website. (39\u0026ndash;42)\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003eSearch results\u003c/h2\u003e\n \u003cp\u003eA total of 2,390 records were identified through electronic searches of six databases and a further four by manual searching of reference lists yielded in our electronic searches. After removing duplicates, 1,846 records were screened by title and abstract, with 148 records eligible for full-text screening and 14 included in our review. Finally, 14 studies are included in this review. The detailed search results are shown in a PRISMA flowchart (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003eOverview of included studies\u003c/h2\u003e\n \u003cp\u003eAll 14 included studies were conducted in LMICs: studies were from five countries in Sub-Saharan Africa (Tanzania, Sierra Leone, Rwanda, Kenya, and Ghana), four countries in South-East Asia (Philippines, Myanmar, Bangladesh, and Cambodia), and two countries in Central America (Nicaragua and Haiti) (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Research on household WTP for sludge collection and transport appears to have increased recently, in the last decade, with all included studies published since 2013. Eleven studies were conducted in urban or peri-urban areas and three in rural areas. Reported average monthly incomes per household ranged from USD 115 to 196 (adjusted for local inflation and expressed in 2022 USD) (39). The 14 studies reported WTP for 34 scenarios that spanned pit and septic tank emptying and CBS (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e\u003cstrong\u003e)\u003c/strong\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003eMethods of the studies\u003c/h2\u003e\n \u003cp\u003eEleven studies employed CV methods, and three employed DCE methods; all included measured and reported WTP (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Among the studies using the CV methods, six studies used open-ended question and six used single- or double-bound dichotomous choice approaches. Two of them combined double-bound dichotomous choice approach and open-ended question by asking two dichotomous questions first and subsequently asking in an open-ended style. Two studies also estimated revealed WTP using real-money voucher trials. These trials involved distributing vouchers offering different levels of discount on desludging fees to households and thereafter estimating the revealed WTP from the number of redemptions, along with stated WTP surveys. (21, 23)\u003c/p\u003e\n \u003cp\u003eThe services for which WTP was investigated can be classified into three groups: manual emptying (with/without manual desludging pump), mechanical (vacuum pump) emptying, and container-based sanitation (CBS). Sludge containment facilities used at the study sites include dry or pour-flush latrines connected to pit (lined/unlined, tyre, drum), septic tanks, and container-based facilities (see more details in Supporting Information 5).\u003c/p\u003e\n \u003cp\u003eRegarding payment methods, two studies investigated the WTP scenarios where respondents pay the emptying fee via a water bill, and two studies examined WTP via monthly payment to service providers. (21, 44\u0026ndash;46) The other studies did not specify the payment method (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eOverview of included studies and WTP elicitation methods.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAuthor \u0026amp; Year\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStudy country\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSetting\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStudy Design\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eType of WTP\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eService for which WTP was investigated\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePayment method\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHarder et al., \u003cspan class=\"CitationRef\"\u003e2013\u003c/span\u003e (44)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePhilippines\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV: single-bound dichotomous choice\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSeptic tank emptying\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWater bill\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRussel et al., \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e (15)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHaiti\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV: single-bound dichotomous choice\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCBS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eJenkins et al., \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e (9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTanzania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV: single-bound dichotomous choice\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eManual desludging pump (Gulper)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eParikh et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e (47)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSierra Leone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV open-ended\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eImproved pit emptying\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBalasubramanya et al., \u003cspan class=\"CitationRef\"\u003e2017\u003c/span\u003e (13)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBangladesh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV: double-bound dichotomous choice\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePit emptying that transports sludge away\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRoss \u0026amp; Pinfold, 2017 (48)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRwanda\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV: Bidding game\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eManual /Mechanical emptying with treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eV\u0026aacute;squez \u0026amp; Alicea-Planas, \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e (45)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNicaragua\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDCE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eExcreta disposal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWater bill\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWorld Bank, \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e (49)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCambodia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRural\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV: open-ended questions (Price Sensitivity Measurement)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck emptying\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBurt et al., \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e (23)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRwanda\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDCE\u003c/p\u003e\n \u003cp\u003eReal-money voucher trial\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated \u0026amp; Revealed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck/manual emptying with group discount\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified \u0026amp; volumetric/flat pricing\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePeletz et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e (21)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV: double-bounded dichotomous choice\u0026thinsp;+\u0026thinsp;open-ended question\u003c/p\u003e\n \u003cp\u003eReal-money voucher trial\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated \u0026amp; Revealed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eManual (formal),\u003c/p\u003e\n \u003cp\u003eVacuum truck emptying\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified \u0026amp; subscription/rent premium\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNaing et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e (50)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMyanmar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV: open-ended questions\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck emptying\u003csup\u003e1\u003c/sup\u003e\u003ca id=\"#FNLinkFn1\" class=\"FNLink\" href=\"#Fn1\"\u003e\u003c/a\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHarper et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e (51)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCambodia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRural\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDCE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eImproved pit emptying\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e (16)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBangladesh\u003c/p\u003e\n \u003cp\u003eGhana\u003c/p\u003e\n \u003cp\u003eKenya\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban \u0026amp; Peri-urban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV: double-bounded dichotomous choice\u0026thinsp;+\u0026thinsp;open-ended question\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCBS, Vacuum truck, Manual (formal)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSingh et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e (46)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBangladesh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrban\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCV: open-ended question\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEmptying services\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMonthly payment\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003csup\u003e1\u003c/sup\u003e WTP for additional service fees to request emptying services through a phone call rather than visiting the administrative office. CV- contingent valuation\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003eGap between WTP and market price\u003c/h2\u003e\n \u003cp\u003eHeterogeneity in service scenarios amongst the studies is caused by factors such as facility type, the number of households sharing one latrine or frequency of emptying. As these metadata were often lacking or reported in a non-standardised form, it is difficult to compare the WTP itself between the studies. Instead, we compare the WTP for a given service as a proportion of the market price or cost of the service (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e\u003cstrong\u003e)\u003c/strong\u003e. We identified 34 WTP scenarios across the 14 included studies, of which nine scenarios (26%) are on manual emptying services, ten (29%) on mechanical pump or vacuum truck services, four (12%) on CBS, while the rest does not specify an emptying method. None of the studies explicitly investigated WTP for informal emptying services. Among the 26 scenarios that reported both mean (or median) WTP and market price (or cost), 20 scenarios (77%) reported that the mean or median WTP did not reach the market price or cost, and 18 scenarios (69%) reported the WTP was lower than half of the market price. While the WTP for one manual emptying and two mechanical emptying scenarios exceeded the market prices, none of the mean WTP for CBS reached the market prices (16% of the price in Haiti, 22\u0026ndash;27% in Kenya, and 66% in Ghana). (15, 16) Therefore, the gap between WTP and market price is an important barrier to households\u0026apos; demand for services.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eWTP amount and the gap between the market price. Mean or median WTP amounts are stated WTP unless otherwise stated as revealed WTP.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAuthor \u0026amp; Year\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eService for which WTP was investigated\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStudy site\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePayment method\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean/median WTP\u003c/p\u003e\n \u003cp\u003e(adjusted for inflation \u0026amp; converted into 2022 USD)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRatio of WTP to price or cost (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eJenkins et al., \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eManual emptying using Gulper pump\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTanzania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 31 /300L (median)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e153% (median)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRoss \u0026amp; Pinfold, 2017\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eManual emptying\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRwanda\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 95 (median)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePeletz et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFormal manual emptying (Gasia Poa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Kisumu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 31 (median)\u003c/p\u003e\n \u003cp\u003eUSD 35 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25\u0026ndash;43% (median)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePeletz et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFormal manual emptying (Gasia Poa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Kisumu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSubscription /rent premium\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRanging from 44% of households willing to pay USD 3 to 12% of willing to pay USD 7 per month\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFormal manual emptying using long-handled bucket\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Kisumu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 29 (median)\u003c/p\u003e\n \u003cp\u003eUSD 34 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27% (median)\u003c/p\u003e\n \u003cp\u003e32% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFormal manual emptying using Gulper pump\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Nakuru\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 44 (median)\u003c/p\u003e\n \u003cp\u003eUSD 49 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31% (median)\u003c/p\u003e\n \u003cp\u003e35% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFormal manual emptying using diesel pump\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Malindi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 49 (median)\u003c/p\u003e\n \u003cp\u003eUSD 60 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e40% (median)\u003c/p\u003e\n \u003cp\u003e49% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFormal manual emptying using long-handled bucket\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGhana\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 39 (median)\u003c/p\u003e\n \u003cp\u003eUSD 54 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31% (median)\u003c/p\u003e\n \u003cp\u003e44% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFormal manual emptying using long-handled bucket\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBangladesh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 12 (median)\u003c/p\u003e\n \u003cp\u003eUSD 18 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13% (median)\u003c/p\u003e\n \u003cp\u003e20% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRoss \u0026amp; Pinfold, 2017\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMechanical emptying with treatment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRwanda\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e~ USD 109 (median)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003efully covered (\u0026gt;\u0026thinsp;100%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWorld Bank, \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCambodia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 14\u0026ndash;19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e39\u0026ndash;55%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBurt et al., \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRwanda\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 88 (revealed WTP)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e152% (95% CI: 120\u0026ndash;208%, mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePeletz et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Kisumu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSubscription /rent premium\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRanged from 52% of households willing to pay USD 2 to 6% willing to pay USD 5 per month\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33\u0026ndash;50% (median)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePeletz et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Kisumu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 21 (median)\u003c/p\u003e\n \u003cp\u003eUSD 22 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33\u0026ndash;50% (median)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePeletz et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Kisumu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 15\u003c/p\u003e\n \u003cp\u003e(mean, revealed WTP)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27\u0026ndash;40% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Kisumu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 20 (median)\u003c/p\u003e\n \u003cp\u003eUSD 21 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34% (median)\u003c/p\u003e\n \u003cp\u003e36% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Nakuru\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 29(median)\u003c/p\u003e\n \u003cp\u003eUSD 32 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33% (median)\u003c/p\u003e\n \u003cp\u003e36% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya, Malindi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 25 (median)\u003c/p\u003e\n \u003cp\u003eUSD 33 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18% (median)\u003c/p\u003e\n \u003cp\u003e21% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGhana\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 39 (median)\u003c/p\u003e\n \u003cp\u003eUSD 38 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e42% (median)\u003c/p\u003e\n \u003cp\u003e40% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eVacuum truck\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBangladesh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 18 (median)\u003c/p\u003e\n \u003cp\u003eUSD 14 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20% (median)\u003c/p\u003e\n \u003cp\u003e24% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRussel et al., \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCBS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHaiti\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 4.5 /month (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCBS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 2.0 (median)\u003c/p\u003e\n \u003cp\u003eUSD 2.0 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22% (median, mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCBS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKenya\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 2.0 (median)\u003c/p\u003e\n \u003cp\u003eUSD 2.4 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23% (median)\u003c/p\u003e\n \u003cp\u003e27% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDelaire et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCBS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGhana\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 3.9 (median)\u003c/p\u003e\n \u003cp\u003eUSD 4.6 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e55% (median)\u003c/p\u003e\n \u003cp\u003e66% (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHarder et al., \u003cspan class=\"CitationRef\"\u003e2013\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSeptic tank emptying\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePhilippines\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWater bill\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 1.8 /month\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e128%\u003csup\u003e2\u003c/sup\u003e\u003ca id=\"#FNLinkFn2\" class=\"FNLink\" href=\"#Fn2\"\u003e\u003c/a\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eParikh et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eImproved pit emptying\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSierra Leone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 80 (mean)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e116%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBalasubramanya et al., \u003cspan class=\"CitationRef\"\u003e2017\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePit emptying that transports sludge away\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBangladesh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e~ USD 7.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e47%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eV\u0026aacute;squez \u0026amp; Alicea-Planas, \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eExcreta disposal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNicaragua\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWater bill\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 3.9 /month\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNaing et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWTP for additional fee to request vacuum truck emptying through a phone call\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMyanmar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 7\u0026ndash;14 (median)\u003csup\u003e3\u003c/sup\u003e\u003ca id=\"#FNLinkFn3\" class=\"FNLink\" href=\"#Fn3\"\u003e\u003c/a\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHarper et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePit emptying that prevents contact with faecal sludge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCambodia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHarper et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePit emptying that produces fertilizer from faecal sludge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCambodia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHarper et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePit emptying that reduces foul odor from high to moderate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCambodia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHarper et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePit emptying that reduces foul odor from moderate to none\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCambodia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot specified\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUSD 23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSingh et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEmptying services\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBangladesh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMonthly payment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e77% said USD 0.9\u0026ndash;4.5 /month\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e107\u0026ndash;535%\u003csup\u003e4\u003c/sup\u003e\u003ca id=\"#FNLinkFn4\" class=\"FNLink\" href=\"#Fn4\"\u003e\u003c/a\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003csup\u003e2\u003c/sup\u003e Calculated by authors based on the most probable scenario (3 years desludging interval)\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e3\u003c/sup\u003e Due to a lack of data on the inflation rate and currency exchange rate, the original WTP amount (in 2017) is shown here.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e4\u003c/sup\u003e Calculated by authors based on the most probable scenario (3 years desludging interval and a 1.96 m\u003csup\u003e3\u003c/sup\u003e average pit volume).\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003eQuality assessment\u003c/h2\u003e\n \u003cp\u003eA quality assessment was conducted for each study using five pre-specified criteria (Supporting Information Table S3). Six out of 14 studies had insufficient sample size or reported no rationales for sample size, and two reported no bias mitigation strategy for starting point bias or price distribution. Regarding survey preparation, five reported no measures to improve validity of the research instruments. For survey implementation, two studies were prone to non-response bias as a large proportion (30% and 42%) of respondents did not answer their WTP (47, 50), two reported no enumerator training or quality control, and six reported nothing about implementation. As for the WTP elicitation phase, five studies did not report econometric models used to elicit mean WTP. After the WTP elicitation, three studies did not assess the validity of the WTP results against income, price levels. One study (Harper \u003cem\u003eet al\u003c/em\u003e) was assessed to be of good quality, while other included studies had one or more points to improve on in the study designs. (51) Moreover, even though Harper \u003cem\u003eet al\u003c/em\u003e minimised biases such as by taking efforts of preliminary testing of research instruments and training for enumerators, they reported that the WTP was likely to be overestimated since their DCE may have caused survey fatigue, primacy effect, and hypothetical bias. (51)\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003eDeterminants of WTP\u003c/h2\u003e\n \u003cp\u003eIn total, there are 20 statistically significant (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) determinants of WTP amongst the included studies (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). In addition to general factors such as education, gender, age and province, the determinants were classified into five groups: economic situation, service characteristics, service accessibility, urgency, and knowledge.\u003c/p\u003e\n \u003cp\u003eThe economic situation determinant suggests that those with higher income show higher WTP (income elasticity). (20) Flat fee is a way of pricing in which customers pay a fixed fee for an emptying event regardless of the amount of sludge removed. A study conducted in low-income settlements in Kigali, Rwanda, reported reduced WTP for flat fee pricing because respondents preferred volumetric pricing. (23)\u003c/p\u003e\n \u003cp\u003eThe urgency category suggests that those who need to remove sludge immediately or more frequently than those who do not are willing to pay more. Both larger household size and sharing latrines by some households lead to a higher sludge accumulation rate, and more people suffering inconvenience when latrines are out of service. Conversely, longer waiting time from requesting a service until it is provided leads to less WTP. As sharing one latrine with multiple households is common in informal urban settlements, the issue of urgency is closely related to their WTP. (9, 16)\u003c/p\u003e\n \u003cp\u003eThe service characteristics category includes the most determinants. Some specific improvements in sludge removal and transport operation are valued (taking away sludge from the latrine to a remote place, preventing odour). Some determinants do not directly benefit customers but benefit emptiers (worker protection, preventing contact with sludge) or society (sludge treatment before disposal, fertilizer production).\u003c/p\u003e\n \u003cp\u003eThe service accessibility category includes factors concerning the physical availability of services. Distance from a road is particularly critical in informal urban settlements as narrow roads and congested buildings often prevent vacuum trucks from operating. (9, 47, 48) In contrast, the determinants in the knowledge category, such as awareness or experience about emptying services, can affect the WTP regardless of whether the service is physically available or not in the area. Education levels were both positively and negatively associated with WTP. (9, 21, 51) While higher education seems to increase valuation of sanitation (51), reasons for the negative association with WTP have not been investigated. (9)\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDeterminants of WTP for faecal sludge emptying services which were statistically significant (at 5% level) in one or more studies.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCategory\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDeterminant\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEconomic situation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eIncome/expenditure (wealth)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePrice (-)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFlat fee (-)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUrgency\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eShared latrine\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHousehold size\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWaiting time (-)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eService characteristics\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBranded service that provides workers with protection\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSmell prevention during the work\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSludge taken away to a remote place\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSludge treated (removing smells and pathogens) before disposal\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eContact with sludge prevented\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFertilizer production\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eService accessibility\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo hygienic emptying method locally available\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDistance from a road\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eKnowledge\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNot knowing any hygienic emptying methods\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eThose who had emptied their latrine using the only available option\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOthers\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEducation (+-)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAge\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGender (male)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eProvince (+-)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e*(-) the WTP decreases as the determinant increases. (+－) means the determinant can either increase or decrease WTP.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eTo our knowledge this is the first scoping review of WTP for sludge emptying services and we identified 14 studies meeting out inclusion criteria. We discuss our results in relation to our study aim: to scope the literature on WTP for emptying onsite sanitation facilities and identify determinants of WTP and gaps in knowledge.\u003c/p\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eWTP elicitation methods\u003c/h2\u003e \u003cp\u003eWe found that CV is the most popular approach for eliciting WTP for FSM services. While CV is flexible and applicable to a variety of scenarios, its disadvantage is that respondents\u0026rsquo; WTP are subject to a hypothesis bias. (24) Stated WTP is usually overestimated relative to revealed WTP, since the respondents hypothetically state their willingness to pay without actual payment. (24) There is also an argument that the hypothetical bias could be relatively smaller in sanitation services than other more complex services or abstract environmental values because the hypothetical services posed, i.e. improved sludge collection, are typically purchased in markets and/or extensions of what respondents have used before. (20) Nonetheless, emptying services are not free from the bias as Peletz et al. reported that stated WTP was higher compared with revealed. (20)\u003c/p\u003e \u003cp\u003eTwo included studies which estimated revealed WTP conducted market experiments using real-money vouchers. In the experiments, a short redemption period, which was three months for both, and logistic complexity were reported as a limitation for eliciting WTP. (21, 23)\u003c/p\u003e \u003cp\u003eNone of the studies used the hedonic pricing method to investigate the WTP for FSM. This method estimates revealed WTP for a certain service or a characteristic using rent or land prices and is commonly applied in the water and sanitation sector. (52\u0026ndash;54) The reason why the hedonic pricing was not employed amongst the included studies could be that emptying services are not constantly provided by houseowners or landlords even in the areas where the owners are financially responsible for the provision (e.g., Kenya, Rwanda, Tanzania). Therefore, the rent may not necessarily reflect the provision of emptying services. (9, 48, 55)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003ePayment method\u003c/h2\u003e \u003cp\u003ePayment methods affect the WTP since their psychological pain, nature of the payment (voluntary or compulsory) and convenience are different. (56, 57) The payment method adopted in the included studies are water bill (two studies) and monthly payment (two studies), and ten studies that did not specify the method are therefore considered as one-time payment in cash. Any sort of taxes or surcharges have not been considered.\u003c/p\u003e \u003cp\u003eSome studies noted that if the market price was spread over the emptying interval, the monthly price would be manageable given the household income, compared to one-time payment. (9, 13) Hence, measures that spread payments over time (e.g., water bills, earmarked savings accounts and monthly subscription) and lower one-time payments (e.g., volumetric pricing (pay-as-you-go)) have been proposed. (23, 49, 58) However, a study carried out in low-income areas of Kisumu, Kenya, reported that WTP for subscription of emptying services with monthly payments was not significantly higher than WTP for one-time payment. (21) These findings imply that payment schemes that are based on the affordability of households at the time of emptying would be more favourable to smaller but continuous payment for low-income people, possibly because they have weak guarantee of future income.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eDeterminants of WTP\u003c/h2\u003e \u003cp\u003eThe set of determinants we presented in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e can be applied as a checklist when improving or introducing new emptying services. In so doing, it is worth noting that some determinants groups are interlinked. First, when households are in urgent situation and want to empty their onsite facility immediately, they may use a service that is more quickly accessible, thereby compromising on emptying quality. Therefore, to capture demand, it is important to keep waiting times short. Regarding the relationship between urgency and economic situation, the more people that share a latrine, the lower the cost per person, but the faster sludge accumulates, which results in more frequent emptying. Hence, future research should consider not only the single household\u0026rsquo;s WTP but also how many households share one latrine when investigating WTP for emptying services. There may however be collective action challenges in shared sanitation situations. (59) Moreover, the category of service characteristics includes determinants that do not directly benefit customers but benefit emptiers or society, such as determinants related to worker protection (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). This finding suggests that users could behave altruistically even if they live in poverty. That said, price tends to increase as the service quality increases, and there could be a trade-off between the two in terms of their impact on WTP.\u003c/p\u003e \u003cp\u003eA potential determinant that has not yet been explored in WTP studies is the thickness or density of the sludge. A systematic review has revealed that thickness of sludge affects choices of emptying technology because the thickness varies depending on sanitation facilities. (27) In general, sludge is thicker and denser in unlined pit latrines than in septic tanks and lined pits due to lack of flushing water, which makes mechanical emptying ineffective. Additional work, as well as cost, of adding water may be needed. (27) Therefore, thickness of sludge could affect WTP for manual and mechanical emptying.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eResearch gaps\u003c/h2\u003e \u003cp\u003eTo date, researchers seem to have focused mainly on understanding the current demand (WTP) for existing services and comparing it with service supply (prices or costs). (13, 47) On the other hand, they have not fully examined WTP for emerging services which try to reduce prices. For example, our review identified four studies which investigated how small payment approaches (e.g., water bill, volumetric pricing, monthly payment) could affect households\u0026rsquo; WTP comparing with one-time cash payment, and only two of them statistically examined the difference in WTP. (21, 23, 44, 46) Therefore, effectiveness of those approaches has not been sufficiently investigated enough. Methods such as group-emptying and scheduled-emptying have recently been proposed to reduce service prices by aggregating the demand of multiple households for efficient operation. (23, 46) However, there are concerns that these methods do not always provide services at the household's preferred timing, which could reduce WTP.\u003c/p\u003e \u003cp\u003eNone of the studies employed mobile money as a payment method. Although the influence of mobile money payment on WTP is a relatively new research topic, it has been reported that mobile money could increase the WTP due to its convenience and widespread use in certain contexts. (60) Mobile money services are already prevalent in Sub-Saharan Africa and Asia. (61, 62) For instance, in Kenyan informal settlements, the vast majority (97%) of respondents to a recent WTP survey had the local mobile money, M-Pesa. (21) Unlike cash, mobile payment can be easily combined with other information technology such as geographic information system (GIS) or behavioural science techniques such as \u0026ldquo;nudging\u0026rdquo;. (58, 63)\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eLimitations\u003c/h2\u003e \u003cp\u003eFirst, although there was no restriction on language, the search was conducted in English so literature published in other languages might have been excluded. Secondly, as this review only included studies with methodologies for WTP elicitation, some peer-reviewed and grey literature with WTP data were excluded. In addition, since the included studies used different methods to elicit WTP and investigated scenarios were heterogeneous, the WTP amounts could not be directly compared. As more studies are conducted in the future, it will be possible to compare WTP amounts in similar settings, which could help improve emptying services.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eRecommendations for future research\u003c/h2\u003e \u003cp\u003eThis is the first scoping review to map existing findings and to identify research priorities regarding WTP for sludge emptying services. Only 14 studies have been conducted in eleven countries. Market prices exceeded WTP in most (77%) cases. with WTP only covering 13%, 16%, and 18% of the prices for manual emptying, vacuum emptying and CBS, respectively in worst cases. This result indicates that households\u0026rsquo; demand for emptying services is hindered by financial constraints in low-income settings. Future research needs to investigate how WTP is affected by interventions that attempt to make services more affordable. It is also worth examining how disadvantage of group-emptying and scheduled-emptying, such as waiting time for service delivery, affects their WTP. In areas where mobile money is prevalent, future research can explore the impacts of mobile payment as well as its application in conjunction with other information technologies or marketing technics. To ensure universal access to safe sanitation by 2030, it is essential that affordable services are available for all, enabling users to safely operate and maintain offsite sanitation systems. Effective interventions that enable low-income communities to implement safe FSM need to be implemented by the public and private sector based on robust evidence including this review.\u003c/p\u003e \u003c/div\u003e "},{"header":"ABBREVIATIONS","content":"\u003cp\u003econtainer-based sanitation, CBS; contingent valuation, CV; discrete choice experiment, DCE; faecal sludge management, FSM; low- and middle-income countries, LMICs; United States dollar, USD; willingness to pay, WTP.\u003c/p\u003e"},{"header":"DECLARATIONS","content":"\u003cp\u003eASSOCIATED CONTENT\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupporting Information\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eThe following information is available free of charge.\u003c/p\u003e\n\u003cp\u003eExample search strategy; List of codes used in the screening process; Components of the data extraction sheet; Results of quality assessment; Characteristics of sanitation management behaviour (PDF); Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) Checklist\u003c/p\u003e\n\u003cp\u003eAUTHOR INFORMATION\u003c/p\u003e\n\u003cp\u003eAuthor Contributions\u003c/p\u003e\n\u003cp\u003eConceived by HT. The screening and data extracting processes were conducted by HT and CM. Analysis was performed by HT. The first draft of the manuscript was prepared by HT. All authors contributed to subsequent drafts. All authors have given approval to the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003eORCID\u003c/p\u003e\n\u003cp\u003eHiroaki Tomoi: 0000-0002-4711-4203, Clara MacLeod: 0000-0001-6952-9103, Taeko Moriyasu: 0000-0002-8201-3061, Sheillah Simiyu: 0000-0003-3069-8967, Ian Ross: 0000-0002-2218-5400, Oliver Cumming: 0000-0002-5074-8709, Laura Braun: 0000-0001-9319-0859\u003c/p\u003e\n\u003cp\u003eNotes\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interest.\u003c/p\u003e\n\u003cp\u003eACKNOWLEDGMENT\u003c/p\u003e\n\u003cp\u003eThis research was funded in whole by the Nagasaki University WISE Programme.\u003c/p\u003e"},{"header":"REFERENCES","content":"\u003cp\u003eExamples of the recommended format for the various reference types can be found at http://pubs.acs.org/page/4authors/index.html. 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Kampala Faecal Sludge Management Improving Faecal Sludge Management for On-site Sanitation.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"London School of Hygiene \u0026 Tropical Medicine","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"onsite sanitation, SDG6, sludge removal, developing countries, operational cost, affordability, economic analysis, willingness to pay","lastPublishedDoi":"10.21203/rs.3.rs-3265808/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3265808/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eUnder Sustainable Development Goal 6, a target (6.2) of achieving universal access to safely managed sanitation services was established. For safely managed sanitation, waste must be safely disposed of in situ or transported and treated offsite. The cost and availability of services to ensure safe management of onsite sanitation, such as pit latrines and septic tanks, can be major barriers for poor households. This scoping review aimed to scope the literature on willingness to pay (WTP) for emptying onsite sanitation and identify determinants of WTP and gaps in knowledge. Through searches of six databases, and after de-duplication, we identified 1,846 studies, of which 14 studies were included after review. Within the 14 included studies we identified 26 distinct investigation scenarios that reported WTP and market price. Among them, 77% (20/26 scenarios) reported that the WTP was lower than the market price. Twenty statistically significant determinants of WTP were identified, which we categorised as economic situation, urgency, service characteristics, service accessibility, and knowledge. The principal knowledge gap was WTP for services designed to reduce prices and/or increase WTP by improving supply-side efficiency or using mobile money. Addressing this gap could help address the challenge of achieving safely managed services for all.\u0026nbsp;\u003c/p\u003e","manuscriptTitle":"Willingness to pay for faecal sludge management services - a scoping review","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-08-16 19:20:34","doi":"10.21203/rs.3.rs-3265808/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"33151497-7a01-475c-a342-7c0e6bb79ae9","owner":[],"postedDate":"August 16th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":24055001,"name":"Environmental Economics"}],"tags":[],"updatedAt":"2024-01-19T15:59:37+00:00","versionOfRecord":{"articleIdentity":"rs-3265808","link":"https://doi.org/10.1021/acs.est.3c06628","journal":{"identity":"environmental-science-and-technology","isVorOnly":true,"title":"Environmental Science \u0026 Technology"},"publishedOn":"2024-01-18 00:00:00","publishedOnDateReadable":"January 18th, 2024"},"versionCreatedAt":"2023-08-16 19:20:34","video":"","vorDoi":"10.1021/acs.est.3c06628","vorDoiUrl":"https://doi.org/10.1021/acs.est.3c06628","workflowStages":[]},"version":"v1","identity":"rs-3265808","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3265808","identity":"rs-3265808","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}