Tucson enters water-sharing agreements with some Phoenix metro cities - The Arizona Republic

Tucson enters water-sharing agreements with some Phoenix metro cities
Sarah Lapidus

Tucson and several Valley communities are entering water-sharing agreements, as future Colorado River water levels continue to worry municipalities.

On Aug. 8, the Tucson City Council passed intergovernmental agreements with Peoria, Scottsdale and Gilbert to store, recover and exchange Central Arizona Project water. The CAP is a 336-mile canal that brings water to many areas around the state.

In the agreement, the communities will store a portion of their CAP water allocation in Tucson's Southern Avra Valley Storage and Recovery Project facility. In times of water shortages, which could trigger cuts on CAP water allocations, those communities would be able to retrieve a portion of Tucson’s CAP supply.

“All of us are working cooperatively to ensure that the Arizonans in central and southern Arizona have a resilient water supply into the future,” said John Kmiec, director of Tucson Water. “By utilizing access infrastructure already built by the city of Tucson, we're providing that resiliency to our sister cities up in the Valley."

Gilbert and Scottsdale have accepted the agreements, while Peoria is likely to address the agreement in September.

Gilbert has agreed to store up to 3,000 acre-feet per year and Scottsdale up to 5,000 acre-feet per year. According to Tucson, Peoria could store up to 10,000 acre-feet per year.

Kmiec said Tucson's system is different than most of the Valley communities. While the other communities have surface water treatment plants, meaning they treat water directly out of the CAP canal, Tucson stores its water in an aquifer system and recovers it as groundwater when needed.

Tucson’s storage facility in Avra Valley lies on an ancient streambed, which provides ideal conditions for recharging water, according to a University of Arizona article.

The Avra Valley Basin to the west of Tucson consists of silt, sand and gravel, where the water can be spread out in constructed recharge facilities so that it percolates quickly into the groundwater table. Kmiec said there is no contamination in the aquifer system.

What is happening to the Colorado River water?

The Colorado River covers more than 246,000 square miles in seven U.S. states including Arizona, and Mexico, and is managed by the U.S. Bureau of Reclamation. Water from this river is primarily used for irrigation, municipal and industrial uses, as well as hydropower production and recreational uses.

The Colorado River water is divided among the seven states and allocated to various cities and industries.

The river shrunk following a two-decade drought, and in 2022 Lake Mead, a Colorado River reservoir that provides water to lower basin states, was at a historic low.

With the most recent wet and snowy winter, Lake Mead levels have rebounded; however, federal officials still want to reserve water in case future drought conditions cause water shortages.

To help preserve the health of the reservoir, Arizona cities agreed to voluntarily leave behind CAP water, including Tucson, which will leave behind 110,000-acre feet of water until 2025.

These cities are following in Phoenix’s footsteps

These agreements come after a series of successful water-sharing pilot projects between Tucson and Phoenix from 2014 to 2017.

“It was a unique agreement to use the aquifers of Tucson to make all parties more resilient,” Kmiec said.

He reiterated that this agreement allows cities to avoid building their own recharge facilities for water they are not currently using.

For many years, Tucson has been purchasing more CAP water than what the city needs and storing it in its aquifers, for use when there may be water shortages in the future.

Scottsdale passed the agreement with Tucson on Aug. 21. According to Scottsdale, this agreement arose out of a need to strengthen water supply resources between cities.

“Interjurisdictional, proactive measures like this benefit Scottsdale residents and show the state that local municipalities are taking forward-thinking action to make sure our communities have water for decades to come,” Scottsdale Mayor David Ortega said in a news release.

Peoria said the City Council will address this agreement in September; until then, its participation is not guaranteed.

"Peoria understands that in order to ensure a stable Colorado River system, this process may result in large temporary reductions to its Colorado River supplies," said Jenna Norris, a water resources policy analyst for the city. "The city of Peoria water utility is committed to exploring all tools to prepare for all potential water futures. This collaborative exchange is just one of them."

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Reach the reporter at sarah.lapidus@gannett.com.

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