CAP shortage will force Tucson to dip into groundwater

Tucson Water customers are not expected to see dry taps or mandatory restrictions in 2027, but the city will take a significant step into a less comfortable water future. Tucson is preparing to use Colorado River water stored underground as a backup for its regular Central Arizona Project supply. The move is necessary because the city’s preliminary CAP order for next year is expected to be about 71,000 acre-feet, less than half of its annual allocation of roughly 144,000 acre-feet and the lowest order in many years.

That amount will not cover the water used by Tucson Water customers. Historically, homes and businesses served by the utility have consumed close to 100,000 acre-feet annually, although this year’s total is expected to be below 95,000 acre-feet. The exact 2027 order has not been finalized and could be between 70,000 and 72,000 acre-feet, said Chris Avery, an assistant city attorney for Tucson Water. Stored supplies will cover most of the shortfall, allowing the city to continue serving customers without an immediate disruption.

The first part of that backup will come from groundwater stored by the Arizona Water Banking Authority. The authority has received approval for Tucson to pump water that it previously recharged underground in the Tucson area. That stored water is available at the city’s Central Avra Valley Storage and Recovery Project, west of Tucson, where recharge basins have been used since the early 2000s to store CAP water and make it available for later pumping.

If necessary, Tucson Water will also draw on CAP water it owns and has stored underground. These supplies are held as long-term storage credits. Artificially recharging water into the aquifer creates credits that allow the owner to pump groundwater in the future without violating Arizona’s restrictions on groundwater pumping. The arrangement has helped Tucson prepare for shortages, but using those reserves now means less will remain for more severe shortages later.

Sharon Megdal, director of the University of Arizona’s Water Resources Research Center, said residents should pay attention to the reduction because it is a real cut, not merely an accounting change. She and other researchers have warned that Tucson and other Arizona communities could face larger reductions if drought and climate change continue reducing Colorado River flows. The city’s use of stored groundwater provides short-term protection, but relying on savings cannot serve as a permanent solution.

Tucson’s decision is also tied to a broader effort to keep more water in Lake Mead. The city plans to leave 50,000 acre-feet there in 2027 and receive about $325 per acre-foot from the federal Bureau of Reclamation, or approximately $16.5 million. Tucson will leave another 2,800 acre-feet as part of a longer-term federal funding arrangement for an advanced water purification project on the city’s northwest side. The proposed project would treat a small amount of wastewater from a Pima County sewage treatment plant for drinking water use, and Tucson is expected to receive about $86 million for it over several years.

Those conservation commitments are separate from the roughly 20,000 or more acre-feet Tucson will lose through the federal reduction in CAP deliveries. The Arizona Water Banking Authority’s stored water will replace that lost supply. Avery said keeping water in Lake Mead is important for Arizona, even if Tucson must pump some of its own stored CAP water. Federal forecasts have raised the possibility that Lakes Mead and Powell could fall so low that their dams would no longer be able to generate electricity.

The city’s situation reflects a much larger conflict over the Colorado River, which supplies cities and farms across seven states and Mexico and supports more than 40 million people. In 2025, the river carried about half its normal flow. Research from the University of Texas at Austin and the University of Colorado in Boulder concluded that human-caused climate change may be producing a lasting decline in precipitation and snowmelt across the West, rather than a temporary dry spell. One study found that warming was responsible for nearly all of the precipitation decline in the western United States over the past three decades.

Negotiations are continuing among the seven Colorado River states and 30 tribes over a replacement for an expiring drought-management plan. Even if the parties reach an agreement, Arizona is expected to face substantial reductions. The state’s relatively low-priority Colorado River rights have already left Pinal County farmers absorbing earlier losses, while cities have been protected through tribal agreements, stored water and temporary federal funding. Those arrangements and federal money are expected to run out by the end of 2026.

For Tucson and other Arizona cities, the immediate choices may include drawing down stored water, asking residents to conserve more, imposing higher rates or adding drought surcharges. Long-term options include expanded wastewater reuse, new groundwater projects and major infrastructure investments that could take years or more than a decade to complete. Tucson is already pursuing advanced water purification, but the broader lesson of the 2027 CAP order is that the city’s reserves are not unlimited. Using its underground savings account will keep water flowing in the near term, while making the need for conservation and new supplies more urgent.