In this paper are shown quantitative and qualitative changes in the drinking water distribution system, occurring in an urban locality with about 200 000 inhabitants in which water consumption over the past decade have been reduced by 50%. In relation to consumer debts are highlighted oscillations related to water pressure in the system and residual chlorine concentration on pressure zones. Hydraulic modeling of the water distribution system was performed using computer programming software, EPANET type, program that performs hydraulic simulations and water quality in pressure pipeline network. After analyzing and interpreting the results of hydraulic simulations performed in different operational situations (consumption 100; 75; 50%) resulted in areas where residual chlorine levels fall well below the limits imposed by the laws and regulations in force. In this situation are required corrective measures on water quality by reducing or eliminating water stagnation by increasing the velocity of the water circulation pipe sections affected. The book is useful for units or operators that use water networks in areas with significant debt fluctuations where by reducing travel speeds on sections of pipeline in areas where residual chlorine drops below the limits, favoring the formation of ecosystems biological and thereby triggering internal processes of auto-pollution reflected in the degradation of water supplied to consumers.