This study proposes to develop methodologies for public water supply quality control by implementing evaluation and control mechanisms and enhancing environmental health surveillance decision-making. These objectives were based on data for waterborne diseases recorded at the Rio de Janeiro State Health Department. We selected the following neighborhoods: Posse (1st Township) and Caioaba (5th Township), with dissimilar situations, allowing us to produce a model of water supply coverage in the Municipality of Nova Iguaçu, Rio de Janeiro State. The study underscored the poor quality of the water supply in the two townships, since 61% of the samples were positive on bacteriological examination, showing the undesirable effects of differential sanitation, especially in developing countries.