One example of testing for water contamination in geographic areas to determine a risk of water contamination includes determining a risk of water contamination. A computer system receives identification of a geographic area in which a risk of water contamination is to be determined. In response, the system determines a number of potential complaints of water contamination in the geographic area by applying the number of one or more correlated sources of water contamination located in the geographic area. The system determines a risk factor representing a risk of water contamination in the geographic area based, in part, on the number of potential complaints. The system can provide the risk factor as the risk of water contamination in the geographic area.