The EpiGEH system monitors outbreaks of waterborne acute gastroenteritis (AGE). It cross-references data from the National Health Insurance Data System (SNDS) with the map of drinking water distribution units (UDI) in France to identify AGE outbreaks potentially linked to tap water contamination. Contamination of distributed water can, in some cases, occur following heavy rainfall that causes runoff, which may be accompanied by an increase in the pathogen load in raw water. The objective of this study was to propose a methodology for constructing and evaluating a rainfall-based indicator and alert system capable of predicting epidemic risk using data from investigated waterborne outbreaks; and, based on this, to identify among the signals from the EpiGEH system those for which the influence of rain was plausible. Data from 30 waterborne WNV outbreaks confirmed by field investigations and occurring between 2010 and 2021 were used to select the rainfall indicator and calibrate the rainfall alarm. For these outbreaks, the influence of rain was considered plausible (positive alarm) when the estimated rainfall indicator exceeded the 4th quintile of monthly precipitation. The rainfall indicator was then applied to the 9,510 signals from the EpiGEH system recorded between 2010 and 2021. Rainfall alert conditions were met for 3.5% of the signals (n=312) with a time lag between the onset of rain and the first cases (rain exposure period) of 15 days (and for 9.3% of the signals (n=837) with a time lag of 21 days). The regions of Provence-Alpes-Côte d'Azur, Corsica, Occitanie, and Auvergne-Rhône-Alpes had the highest proportions of signals associated with a positive rainfall alert (ranging from 11.0% to 14.5%).For alerts associated with a positive rainfall alarm, the average time between the rainfall threshold being exceeded and the first cases of waterborne disease from the detected outbreak appearing was 5.4 days. The main value of these analyses lies in the ability to identify, among the signals detected by the EpiGEH system, those for which the vulnerability of drinking water production systems to precipitation played a decisive role. The corresponding water distribution units should be prioritized for action to strengthen their resilience to adverse weather conditions, thereby better safeguarding against the risk of epidemics. Further studies incorporating land-use and land-cover data would be necessary to refine the link between rainfall and the risk of waterborne WNV outbreaks.