Meteorological Influence on Drinking Water Quality: Microbial Variability in Groundwater Wells and Piped Distribution Networks from Western Romania

Climate variability plays a crucial role in shaping drinking water quality, yet the quantitative links between meteorological factors and microbiological contamination remain underexplored in temperate continental climates. A secondary data analysis was conducted on 15,394 microbiological water quality test results collected between 2015 and 2024, including heterotrophic plate counts (22 °C and 37 °C), coliform bacteria, and <i>Escherichia coli</i>, and their associations with local meteorological conditions across groundwater wells and piped distribution networks were examined. A clear distinction emerged: groundwater wells showed higher vulnerability to primary microbial contamination (coliforms and <i>E. coli</i>), whereas distribution networks exhibited higher odds of heterotrophic plate count exceedances, indicating greater susceptibility to post-treatment microbial regrowth. In groundwater wells, temperature showed strong positive associations with all microbial indicators (<i>p</i> < 0.001), with pronounced summer peaks in coliforms and <i>E. coli</i>, while precipitation triggered short-term contamination spikes characterized by a 2-day lag. In contrast, piped networks exhibited weaker and more delayed meteorological responses. These results highlight the need for a shift from climate-responsive to climate-pre-emptive water quality monitoring by incorporating meteorological forecasts, especially for non-chlorinated groundwater sources.