Climate hazards expose distinct compliance vulnerabilities in US drinking water systems

Climate extremes threaten drinking water systems. Whether climate hazards compromise drinking water regulatory compliance, and through which pathways, remains uncharacterised at national scale. We linked extreme precipitation, heat intensity, and wildfire smoke PM_2.5 to monthly Safe Drinking Water Act violation risk across twelve contaminant categories in 56,351 community water systems (2006-2020). Extreme precipitation produced the broadest disruption, increasing turbidity, coliform, disinfection byproduct and treatment-technique violations by 8-13%, concentrated in surface-water and smaller systems. Heat showed a narrower, microbial-specific signal: Escherichia coli (E. coli) violation risk increased ~2.6% per °C, though the pathway could not be mechanistically isolated. Wildfire smoke associations were fragile: pooled estimates attenuated under strict seasonal controls, and only an exploratory transport-distance probe remained positive. These findings reveal a graded evidence hierarchy, precipitation robust, heat selective, smoke provisional, arguing for climate-responsive monitoring triggers matched to hazard-specific evidence strength, including post-precipitation follow-up for smaller systems.