There are a number of free and commercial software tools for water supply network modelling that are suitable for assisting with the management of urban water supplies. These include EPANET, Aquis, WaterGems, Synergi, WaterCAD, Infowater, amongst many others. EPANET is free and is a good place to start, and determine exactly what you require, before committing to more costly options. It is also common to integrate modelling engines with GIS systems.