The authors have constructed a mathematical model for the cause-and-effect relationship between acute enteric infection (AEI) morbidity and the levels of water bacterial contamination and the properties of microorganisms. New procedures were proposed to calculate a risk for water-borne AEI depending on the sanitary-and hygienic conditions of water use and the degree of water contamination in the direct isolation of the causative agents of pathogenic and opportunistic infections, which allow the calculation and prediction of the occurrence of AEI at the individual and population levels.