Computer modeling can greatly improve the planning and operation of water systems at relatively low cost. Time-dependent water system models can be used to refine improvements to a water supply and distribution system, and micro-and mini-computers now have the ability to handle many such models. In a recent study for the City of Fullerton, California, a time-dependent computer model identified needed new facilities and operational improvements to the water supply system that can save the city a considerable amount of money. The computer model enabled the city and its engineers to identify ways to maximize use of low-cost well water and reduce the amount of pumping (and energy use) throughout the system.