Exploring the Underlying Influences of Daily Water Intake Using the Situated Assessment Method

The adverse impacts of underhydration call for a better understanding of what facilitates and hinders water drinking to better inform intervention efforts. We used the Situated Assessment Method, a quantitative approach for profiling behaviours and their underlying influences, to extend previous research on what influences water drinking in daily life. We assessed the underlying influences of 213 adults’ water intake in the UK across various everyday situations, such as during work and dinner. Participants reported the extent to which 13 potential underlying influences of water drinking, such as thirst or the availability of other drinks, impacted their water drinking behaviour and their typical water intake across 10 situations. During a one-week follow-up, they also reported their actual water intake in these situations over three alternating days. We then assessed (1) how varied water intake and its underlying influences were across individuals and situations and (2) the cross-sectional and prospective relationship these influences had with typical and diary water intake, respectively. Our results show that water intake varied greatly between individuals and situations and within individuals across situations, providing further evidence that this is highly situated behaviour. Additionally, the 13 underlying influences we identified individually explained substantial proportions of the variance in water intake. Notably, habitualness (e.g., subjective effort), self-relevance (e.g., health consciousness), and immediate feedback (e.g., taste) were positively associated with water intake. However, the ability of these underlying influences to facilitate water intake varied widely based on their presence across individuals and situations. These results suggest various interrelated influences underlie water drinking behaviour, evidencing the importance of using comprehensive theories of behaviour to inform research in this domain. Additionally, interventions may benefit from personalised intervention strategies and promoting the various rewarding outcomes people associate with water intake.