Longitudinal Assessment of Flood Impacts on Water and Sanitation Resilience: Satellite Based Evidence from Community Health Units in Kilifi, Kenya

Background Flooding can disrupt water, sanitation and hygiene (WASH) services in low income rural and peri urban settings. Yet there is limited quantitative evidence on how repeated flood exposure affects safe water and sanitation over time at the level of Community Health Units (CHUs), which are the operational units for primary health care in Kenya. Methods We analyzed data from ten CHUs within the Kaloleni Rabai Demographic Health Surveillance System (KRDHSS) in Kilifi County, Kenya, across eleven rounds from 2017 to 2024. For each round we calculated the percentage of households with safe drinking water and a functional latrine and defined flood exposure as the percentage of CHU area flooded in the previous month using Sentinel 1 radar. We fitted linear mixed effects models with CHU random intercepts, adjusting for land cover and elevation, and constructed flood adjusted resilience scores for safe water and latrine access. Results We obtained 220 CHU round observations. A one standard deviation increase in flood frequency was associated with a larger decline in functional latrine coverage than in safe water coverage (coefficient = 5.63; 95% CI: −9.33 to − 1.93; p = 0.003). The interaction between safe water access versus functional latrine access and rural setting was strong (coefficient = 38.90; 95% CI: 30.82 to 46.99; p < 0.001), with rural CHUs having lower safe water coverage but only slightly lower latrine coverage than peri urban CHUs. Resilience scores showed a clear gradient, with peri urban CHUs generally ranking near the top of the distribution and rural CHUs clustering toward the bottom, particularly for safe water resilience. Conclusions Repeated flooding undermined functional latrine access more than safe water access, and rural CHUs were markedly less resilient to flood related WASH disruptions than peri urban CHUs. CHU level resilience scores and maps provide a practical tool for identifying low resilience clusters and can guide targeted investments in resilient water systems and flood resistant sanitation in coastal Kenya.