Epidemiological studies focusing on the risk of fecal contamination in the public water supply in France are rare. They tend to focus on epidemic risk, and more rarely on endemic risk in large cities. However, they neglect the hyperendemic risk, which nevertheless accounts for the majority of the health impact and is concentrated in France in distribution units (UDIs) serving 100 to 10,000 residents, or 24,000,000 in total. Precipitation largely determines this risk. Data from the National Inter-Regime Health Insurance Information System (Sniir-AM) offer a unique opportunity for syndromic surveillance of hospital-admitted cases of gastroenteritis (GEAm). These data enable the modeling of age-standardized GEAm incidence by day and by municipality, based on water microbiological quality (SISE-Eaux health monitoring database) and precipitation, while controlling for numerous risk factors documented elsewhere. This model could support a wide range of public health objectives: the proportion of GEAm attributable to distributed water, identification of UDI and at-risk UDI categories, characterization of associated risk factors, temporal monitoring of risk and risk factors in the context of climate change, and finally evaluation of public action, such as the implementation of Water Safety Plans (WSP).