The Phoenix City Council has approved a 10-year partnership with Salt River Project to help ensure resiliency in the Valley’s water supplies in the future during extreme drought and shortage conditions on the Colorado River.

The agreement, the second of two partnerships signed this year between SRP and Phoenix, will compliment a first-of-its kind water agreement approved by the SRP Board and the Phoenix City Council in March. Under terms of the latest partnership, SRP has agreed to provide Phoenix with access to additional storage capacity in certain SRP-owned and -operated underground water storage facilities. This allows Phoenix to store currently unused portions of its annual allocation of Colorado River water for later recovery during potential shortage events.

“Providing an ample and reliable water supply continues to be one of Phoenix’s highest priorities,” said Mayor Thelda Williams. “This partnership with SRP is a smart and creative plan to safeguard against continued drought and will allow us to use our stored water supply in future times of shortage.” 

Phoenix is the largest of the Valley cities that partner with SRP in the Granite Reef Underground Storage Project (GRUSP), located on Salt River Pima-Maricopa Indian Community land in the Salt River bed just west of SRP’s Granite Reef Diversion Dam. The other municipal partners in GRUSP are Scottsdale, Tempe, Mesa, Chandler and Gilbert. Phoenix is also one of SRP’s largest customers that participate in SRP’s Groundwater Savings Facility, where participants deliver Central Arizona Project water from the Colorado River to SRP in lieu of pumping groundwater. 

“These two agreements with Phoenix are examples of the type of regional partnerships that are necessary to ensure a reliable and adequate water supply during these times of drought and possible future shortages on the Colorado River,” said SRP President David Rousseau.  “In working with Valley cities such as Phoenix, these two recharge facilities offer a combined total storage volume of nearly 150,000 acre-feet per year that will allow all of us to take further advantage of the infrastructure investments that have been made over the last 25 years.”

GRUSP and SRP’s Groundwater Savings Facility enable Arizona to maximize the use of its Colorado River entitlement and help the state reach its “safe yield” goal. Safe yield is the equilibrium between the amount of groundwater pumped from an aquifer and the amount recharged into it.

Through artificial groundwater recharge, water is retained in huge, porous earthen basins and allowed to seep into the natural underground aquifer below. An aquifer is the porous material in which water is contained underground. It can consist of gravel, fractured rock, sand, silt or a blend of such materials and vary in thickness from a few feet to 1,000 feet or more. Water is stored in the aquifer and withdrawn by well-pumping when needed. For a diagram of the GRUSP facility and for more information about how underground water banking works, visit         

In the first agreement finalized in the spring and effective on July 1, SRP agreed to reserve capacity in its extensive system of wells for future use by Phoenix to recover long-term storage credits for Colorado River water that is stored within SRP’s water service area. Water stored and recovered through these two partnerships can be used anywhere within Phoenix’s Water Service Area.

The largest provider of water and power to the greater Phoenix metropolitan area, SRP is the nation’s oldest multipurpose water reclamation project and operates and maintains an irrigation system that typically delivers more than 325 billion gallons of water to Valley municipal, industrial, agricultural and urban irrigation systems each year. SRP’s system of dams, canals and groundwater wells allows it to store water during wet periods so that it has enough to meet demand during the dry periods that are common in the desert.