A practical water–energy–climate solution for sustainable and resilient coastal cities: smart use of seawater in municipal services

Abstract Municipal services for buildings in developed (sub)tropical coastal cities contributed 18% of greenhouse gases (GHGs) in 2020. One mitigatory solution is the direct use of seawater for district cooling and toilet flushing, which has been applied in Hong Kong on various scales and achieved 30% water and energy savings. However, no systematic evaluation and strategy for this solution are available. Herein, we develop a high-resolution quantitative scheme to elaborate the co-benefits and optimal strategies for expanding this use of seawater. We find that in Hong Kong, Jeddah, and Miami, using local seawater at the city-scale would achieve life-cycle GHG mitigation (42%–56%), energy savings (45%–49%), and freshwater savings (11%–43%). High-resolution analysis reveals that population density and district marginal performance are essential to optimize the efficiency of seawater use. Our scheme confirms the utility of seawater for municipal services and is an effective tool for innovative municipal-service enhancement.