The Salt River Project (SRP), the largest water purveyor of the Phoenix metropolitan area, operates two large ground water recharge facilities: the Granite Reef Underground Storage Project (GRUSP) and the New River-Agua Fria Underground Storage Project (NAUSP).  The GRUSP has been in operation for twelve years and has stored nearly 1,000,000 acre-feet of water.  It is the largest underground storage facility in Arizona with a capacity in excess of 100,000 acre-feet per year. Water stored at GRUSP is from two sources: Colorado River water delivered by the Central Arizona Project Aqueduct (CAP water) and water from the Salt and Verde Rivers (SRP water). Recharge at GRUSP is by water-spreading in seven basins with a total surface area of 225 acres.  The basins are constructed on the dry channel of the Salt River, three miles downstream of SRP’s Granite Reef Dam.  All water to be stored is delivered by gravity.  Recharge rates range from three to seven feet per day.  The site was selected because of its very favorable hydrogeologic characteristics.  The vadose zone and aquifer underlying the facility are part of a thick alluvial fan composed mostly of unconsolidated coarse detritic sediments at the base of the Mc Dowell Mountains.  The NAUSP is designed for a storage capacity of 75,000 acre-feet per year.  It consists of six off-channel basins.  Total infiltration surface is 180 acres.  Recharge rates exceed 2.5 feet per day.  The site was selected on an area of thick alluvial sediments that are part of the valley of the Agua Fria River and very favorable for recharge and underground water storage.  The GRUSP and the NAUSP are an integral part of the large water resources management system of the SRP.