WEAP

WEAP (the Water Evaluation And Planning system) is a Windows-based decision support system for integrated water resources management and policy analysis. WEAP is a model-building tool, used to create simulations of water demand, supply, runoff, evapotranspiration, infiltration, crop irrigation requirements, instream flow requirements, ecosystem services, groundwater and surface storage, reservoir operations, and pollution generation, treatment, discharge and instream water quality, all under scenarios of varying policy, hydrology, climate, land use, technology and socio-economic factors. WEAP can dynamically link to the USGS MODFLOW groundwater flow model and the US EPA QUAL2K surface water quality model.
WEAP was created in 1988, and continues to be developed and supported by the U.S. Center of the Stockholm Environment Institute, a non-profit research institute based at Tufts University in Somerville, Massachusetts. It is widely used for climate change adaptation studies, and has been applied by researchers and planners in hundreds of organizations worldwide. 
WEAP is distributed at no charge to non-profit, academic and governmental organizations based in developing countries. 