In general, a storage and recovery project stores surface water (in this case, Colorado River water) in the ground and recovers it for use at a later date. In the Tucson area, the water table is far below land surface. This means there is a large vertical section of soils with ‘empty’ pore space between the top of the aquifer and the surface of the land. This dry vertical section of soils is called the vadose zone.
Colorado River water is released into constructed basins to percolate naturally through the vadose zone until it reaches the underground water table and mixes with native groundwater. This raises the top water table higher into the vadose zone. Many of these projects are designed to store river water underground for use in the future. As more water is recharged, the water table continues to rise. Using the vadose zone as a huge, underground water bank allows Tucson to store a much larger volume of water than the city ever could using above-ground reservoirs. At CAVSARP, specially-designed wells have been constructed to recover the stored, blended water and deliver it to Tucson Water customers.