Providing a reliable and affordable source of water in the desert has never been an easy task. Not only does it require careful planning and solid infrastructure, it requires partnerships. 

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By Christa McJunkin 

Just as the landowners and farmers who banded together to work with the federal government to form the Salt River Project (SRP) 100 years ago knew, one simply cannot survive in the desert by going it alone. That is why, a century later, SRP continues to look for partnerships that will assist it to deliver affordable and reliable water not only to its own customers but to others as well. 

One example of a successful partnership is the interconnection between SRP’s water system and that of the Central Arizona Project (CAP). Delivering a combined 2.3 million acre-feet of water per year to more than 5 million Arizonans, the interconnection helps SRP and CAP manage the water resources that support central Arizona’s communities and economy. 

The CAP water system begins with intake pumps at Lake Havasu, Arizona, that divert Colorado River water into the CAP canal, a 336‑mile-long aqueduct system stretching from Lake Havasu through Phoenix to south of Tucson. The CAP canal delivers about 1.5 million acre-feet of Colorado River water each year to cities, agricultural users, and tribal communities in c entral and southern Arizona. 

SRP delivers more than 800,000 acre-feet of water annually from a watershed located in northeastern Arizona to more than 2.5 million people in 10 cities and towns, including both residential and agricultural customers. 

In 1989, the CAP-SRP Interconnection Facility (CSIF) was constructed. This one-way interconnection from the CAP canal to SRP’s water delivery system has a total capacity of 1,200 cubic feet per second. This connection allows CAP water to be delivered to any point along more than 1,200 miles of SRP canals and laterals, including recharge facilities and the 11 drinking water treatment plants used to provide safe, reliable drinking water to Phoenix and its suburbs. 

“The CSIF has provided additional flexibility for CAP water users to have access to their CAP water. It is a testament to thoughtful investment in infrastructure and how collaborative solutions can support water user needs to meet their demands,” says Patrick Dent, the CAP water policy director. 

Since the CSIF was first used in 1990, a total of 3.4 million acre-feet of CAP water has been transported through it. More than half—1.8 million acre-feet—has been recharged underground for future use at three recharge facilities operated by SRP. While most of the remaining 1.6 million acre-feet has been transported to city water treatment plants and put to other municipal uses, some of the water has been exchanged between SRP and CAP during times of extreme drought or system maintenance. 

From 2000 to 2004, a time of extreme drought in the Salt and Verde watersheds, SRP was faced with the prospect of empty reservoirs despite having reduced water allocations. This dire situation was avoided through the purchase and exchange of more than 600,000 acre-feet of CAP water to supplement SRP’s water supplies from 2000 to 2004. 

In 2019, SRP was able to reciprocate by supporting CAP during a major system maintenance project. In that year, the Salt River siphon, which moves CAP water under the Salt River, needed to be drained so that its lining could be inspected and repaired. Since the siphon is located upstream of the CSIF, any CAP water orders that would normally be delivered via the CSIF could not be made unless CAP and SRP worked together. In preparation for the siphon outage, SRP and CAP operational staff collaborated on a plan by which SRP would take delivery of additional CAP water prior to the siphon outage and then would be able to maintain delivery of CAP water orders during the siphon outage. The collaboration was a great success. 

The leadership of both SRP and CAP realized a long time ago that they could help each other both in times of severe dry periods and when water was in abundance and do it in an efficient and cost-effective way. In order to facilitate expanded delivery and to enhance the resiliency of the Salt River Valley’s water supplies, the construction of a new SRP-CAP interconnection facility (SCIF) has been proposed. This interconnection would flow in the opposite direction of the existing CSIF, and much like that facility, it would be a critical component of the valley’s water delivery infrastructure. The purpose of the SCIF would be to push water to areas where it’s needed in central Arizona. 

One use for the SCIF would be to deliver water held in the 287,000 acre-feet of storage capacity in the New Conservation Space (NCS) at SRP’s largest reservoir, Roosevelt Lake. NCS water is stored at the dam by the cities of Chandler, Glendale, Mesa, Phoenix, Scottsdale, and Tempe and is intended for use outside SRP’s service area. Using the SCIF would eliminate the need for additional infrastructure to move this water outside SRP’s service area. 

With the SCIF in place, NCS water and other water supplies could be delivered directly to city water treatment plants located along the CAP canal. The parties involved would coordinate operations to facilitate the use of the CAP canal without affecting other CAP deliveries, likely providing additional operational flexibility. “The SCIF will provide significant operational and water reliability benefits for water users served by both CAP and SRP,” says Mr. Dent. 

Perhaps most importantly, the SCIF will enable the recovery of water stored underground at recharge facilities located within SRP’s water service area. Like the surface water stored in SRP’s reservoirs, recovered well water can currently only be delivered using SRP’s delivery system. That presents a problem, considering that the vast majority of this water is intended to meet needs outside SRP’s service area, including those related to future growth or shortage conditions. With the new interconnection in place, cities like Phoenix, which holds credits for more than 200,000 acre-feet of water stored underground within SRP’s service area, can arrange to use SRP’s wells for recovery. One or more wells would pump Phoenix’s stored water and deliver it to SRP customers in place of the SRP water they would normally receive. 

These interconnections offer valuable benefits such as an infrastructure solution, significant cost savings to cities, and a secure water resource management tool that provides added resiliency. And with a joint vision of the future and the goal of being prepared for uncertainty and able to work in partnership, SRP and CAP continue to collaborate to ensure a reliable and sustainable water future for their customers. 

Christa McJunkin is the director of water strategy at SRP. She can be contacted at