Water quality modeling has become a recurring request from drinking water network managers, due to regulatory changes but also to contribute to satisfaction for all the users for the taste of water. The objective of this research project is to provide network managers, both for the understanding of the phenomena studied and for the technical valuation of the approaches considered, a new methodology to develop a predicting method for free residual chlorine concentrations using an accurate hydraulic model. The development of the chlorines model needed knowledge of the network's hydraulic behavior. The model established can be used in a proactive and daily mode of operation, it is helpful to show the quality of drinking water, particularly chlorine concentration, during peak demand and the lowest demand times before it is found in the distribution network district hydraulic part. Based on the results of this simulation we have identified a low content of free chlorine in the cast iron pipes, due to the high consumption of chlorine by the ferrous ions (Fe2 +) which generates a significant vulnerability of consumers. The results showed that the proposed approach could make it easier for the utility managers to efficiently optimize residual chlorine in large water distribution networks (WDN).