The public water supply is a constant subject of concern since its quality depends on many different factors. The intention of this paper was to evaluate the quality of the public water supply in 38 cities from the midwest region of the State of São Paulo, Brazil, during the year of 2016. The parameters investigated included free residual chlorine, pH, apparent color, turbidity, fluoride, nitrate, and the presence of total coliforms and Escherichia coli. In total, from the 2,897 samples of water under analysis, 545 (18.81%) samples conflicted with the country's current legislation. The highest rates of noncompliance were related to fluoride contents and the presence of total coliforms. In addition, high nitrate concentrations (>10 mg/L NO3‐N) were observed in one of the cities’ water sample. Our data display the major critical points of the water offered to the population and expose the potential risks for human health, indicating the need of a regular surveillance of the water and the adoption of corrective and preventive measures, in order to avoid the waterborne diseases occurrence, thus contributing to the population's health improvement. Practitioner points Approximately 20% of the unsatisfactory water samples. High nitrate concentrations in public supply water. Potential risks for human health.