This easy-to-use analytical tool can be used to evaluate the energy and greenhouse gas implications of water management decisions. The Excel-based model allows the user to explore a range of possible scenarios, such as increased demand for water resources, the development of alternative water and energy sources, and needed water treatment improvements resulting from emerging contaminants and stricter water-quality guidelines. WESim can be applied by individual water and energy utilities, groups of utilities, and policymakers and decision makers.