The Water Evaluation and Planning System (WEAP) aims to incorporate concerns about allocation of limited water resources, environmental quality, and sustainable water use into a practical tool for water resources planning. As a database, WEAP provides a system for maintaining water demand and supply information. As a forecasting tool, WEAP simulates water demand, supply, flows, and storage, as well as pollution generation, treatment, and discharge. As a policy analysis tool, WEAP evaluates a full range of water development and management options and takes account of multiple and competing uses of water systems.