For several years, Santé publique France has been conducting research based on health insurance reimbursement data to improve the detection of hospitalizations due to acute gastroenteritis linked to the consumption of tap water. This work is part of a project to establish a nationwide automated detection system for clusters of hospital-treated acute gastroenteritis (GEAm) cases of waterborne origin. The public health value of automated detection of GEAm case clusters lies in its potential for risk prevention through the identification of water distribution units (WDUs) suspected of being the source. Identifying these WDU will help determine the risk factors and circumstances underlying the cluster. The objective of this study was to evaluate and compare the performance of two methods for detecting GEAm outbreaks using health insurance data to identify the affected WDU. The methods evaluated were Kulldorff’s spatio-temporal scan statistic and the geographic comparison of incidence rates method. The simulation study was based on Noufaily’s method. Three departments were used as the basis for the analysis: Puy-de-Dôme, Isère, and Gironde. One thousand simulations were performed per department. Health insurance data were used as reference data for the baseline simulation of acute gastroenteritis. Subsequently, the detection methods were applied to the simulated data. Sensitivity and the false alarm rate were used to compare the performance of the two detection methods. This work led to the selection of a detection method: Kulldorff’s spatio-temporal scan statistic. The results of this study suggest good detection capability, regardless of the time of year, for outbreaks involving at least 10 cases of waterborne acute gastroenteritis (WAG). Detection capability is very low when there are fewer than 5 waterborne GEAm cases. The selected method will be applied to real-world data as part of a pilot study and a working group on "the link between the detection of GEAm case clusters and field investigations." The identification of an effective method for detecting waterborne outbreaks and the pilot study to test the application of surveillance in the field—including the link with environmental investigations by the ARS—enables the consideration of retrospective surveillance of waterborne GEAm outbreaks across the entire country using health insurance data.