Extreme Rainfall Modifies the Association between Piped Water Intermittency and Water Quality in Low-Resource Settings

Intermittent water supply (IWS), where piped water is not continuously available, can compromise water security and quality. Extreme rainfall may exacerbate these risks by enabling microbial contaminants to enter distribution systems. We assessed the association between household piped water intermittency and Escherichia coli concentrations in drinking water samples sourced from piped systems (n = 1098) and whether extreme rainfall events (>90th percentile) modified this relationship. Participants included 234 households from six Ecuadorian communities in the ECoMiD birth cohort. We measured intermittency as days/week, hours/day, and hours/week without water supply. Households in IWS communities had significantly more contaminated water samples than those in the city, which had a nearly continuous water supply (CWS) (OR: 10.4 [95% CI: 5.9–18.4]). Extreme rainfall modified the association between IWS and water contamination (p for interaction = 0.014): each additional day without water was associated with 42% higher odds of contamination when an extreme rainfall event occurred within 4 days prior to sampling (1.42 [1.09–1.84]). Effect modification was also observed for rainfall lag windows of 3–7 days but not for other intermittency definitions. These findings suggest that more frequent water service interruptions per week may exacerbate household vulnerability to extreme weather events, reinforcing the need for a resilient, well-maintained water infrastructure.