Population growth and sewage from urban, industrial and agricultural population waste disposal site leachate and runoff caused the pollution increasing and limiting water resources. Model is a quantitative expression of the system. Model can be as simple as a pipeline system (physical model) or as complex as a three –dimensional mathematical representation which is needed to solve hundreds of equations with a large computer. The aim of this study was to evaluate the effect of the wall reaction coefficient in water distribution system by EPANET software. This software uses flow equations and mass transfer to simulate water quality in water delivery network methods used to build the model of the application and entering the required data and then running the model in several different scenarios which in every trial, the affection of wall reaction rate on chlorine concentration, transferring and water age were assessed. The results showed that the ratio of this coefficient is important in calculating concentration in network and must be more considered and also is important in chlorine concentration and transferring. Also it can be said that EPANET is effective on simulating pipe wall reaction.

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