When water leaves the treatment plant, it is at its peak of quality. With time, the disinfectant residual decreases, possibly with increase in microbial activity. Changes in quality may be caused by biological or chemical transformations, by mixing of waters from different sources, or by a loss of system safety. Until recently, there is no much research has been made to the problem of changes in water quality in distribution system especially in Egypt. This paper applies WaterCAD simulation model to modeling water quality in Benha City distribution system and compares the results to field data. This software implements the Eulerain Discrete Volume-Element Method (DVEM) to solve the numerical constituent transport problem for the system being analyzed. Model is used to predict the propagation of chlorine residual in six portions of the Benha city distribution system. Good correspondence with observed chlorine residuals is obtained at locations where the hydraulics is well characterized. It was found that using a different wall decay constant for pipes in a network might be suitable for all distribution systems. Field quality data is important in developing and understanding predictive models.