Identifying microbial and physicochemical risks affecting the quality of potable water supplied by selected shallow groundwater wells in Finland

Water samples were taken from 28 groundwater wells situated in shallow aquifers used as sources of potable water in the North Ostrobothnia, North Savo and Lapland regions of Finland. These were mostly small-scale wells in sparsely populated areas. Water samples were assessed for physicochemical water quality, microbial indicators, stable water isotopes (d18O and d2H) and bacterial community composition (using 16S rRNA gene amplicon sequencing). The aim of the study was to characterise the water from these wells in microbial and physicochemical terms, to identify outlier wells, and to reveal links between microbial, physicochemical and environmental variables that might prove useful in predicting and preventing contamination events and identifying potential contamination sources. DNA and cDNA amplicons and physicochemical water quality data varied between wells, nearby water quality risk factors were common (fields, peatlands, roads, ditches, buildings and surface water sources), and stable water isotope analysis revealed indications of surface water intrusion in five of the wells. Well location coordinates recorded here are approximations. Exact coordinates are not given for reasons of confidentiality and to safeguard the water supplies.