Microbiological quality of drinking water in northern communities: Influence of source water and treatment processes

Climate-driven permafrost thaw and altered precipitation, combined with reliance on limited water sources and treatment infrastructure, challenge the microbiological safety of northern drinking water. However, the interplay between water bacterial composition, treatment methods, and dissolved organic matter (DOM) remains overlooked in these systems. We investigated bacterial community composition from source to tap in eight northern communities across Nunavut, Nunavik, and the Northwest Territories, and its association with DOM and nutrient composition, to provide a comprehensive understanding of bacterial ecology and potential water safety vulnerabilities in northern drinking water systems. We hypothesized that: (1) source water bacterial composition varies with DOM composition; (2) bacterial composition in supply systems reflects source conditions and; (3) shifts with treatment, reflecting community-specific procedures. Our study reveals that drinking water overall bacterial composition is driven by DOM and nutrient composition, and shifts along supply systems, with community-specific patterns of reduction/increase in bacterial abundance from source to tap. These results underscore the necessity of regular monitoring to identify microbiological risks linked to environmental changes affecting DOM and the need to address community-specific vulnerabilities, such as bacterial regrowth, related to treatment processes. These findings enhance our understanding of northern microbiological water quality dynamics, informing targeted public health interventions.