A water reuse planning model has been developed for use in determining the optimum reuse of waste‐water on a regional basis that minimizes the overall cost of water supply for single period planning. Wastewater from all use sectors, along with fresh water, are considered as candidate sources or origins of water for other elements within the use sector and also for elements of other use sectors. Quality parameters of various sources of flows are explicitly considered. The model allows for economies of scale in treatment and transportation through the use of a nonlinear objective function and consists of both linear and nonlinear constraints. The model is solved using a large‐scale generalized reduced gradient technique. The analysis of hypothetical examples shows how the model can evaluate various planning scenarios, allowing the planner a broad spectrum of solutions to choose f