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The city's preliminary order for Central Arizona Project water next year is now scheduled to be for about 71,000 acre-feet, its lowest in many years. That's a little less than half of the city's annual CAP allocation of about 144,000 acre-feet. 

But despite the cut, city residents and other Tucson Water users won't face any problems turning on their taps at home or at work, officials say. That's because the city will make use of CAP water that's been stored underground to fill the gap between customers' demands for water and the available supply.

But reaching into these reserves means less stored groundwater will be available in the future when additional CAP cuts occur, says a top University of Arizona water researcher, Sharon Megdal.

She and other researchers have warned that Tucson and other Arizona cities will face deeper cuts in the future, if the ongoing drought and climate change continue to reduce Colorado River flows as they have since about 2000.

There will be no water shortages in Tucson next year in part because the city has obtained approval from a state agency to pump enough stored groundwater, to which the agency owns the rights, to make up most of the difference in customers' use and the CAP supply coming to the city via canal.

The remaining gap will be filled, if necessary, by CAP supplies that Tucson Water has itself stored underground for future use during shortages, said Chris Avery, an assistant city attorney for Tucson Water.

All these stored supplies are officially classified as long-term storage credits. The existence of the groundwater that was deliberately stored through artificial recharge allows the owners of the credits to pump out groundwater elsewhere without running afoul of state groundwater laws that restrict pumping.

Megdal, director of UA's Water Resources Research Center, said about the CAP cut to Tucson, "The cuts are real. People should take notice!" Megdal has already urged Tucson Water and other water users in this area to make additional cuts in their use now to ensure there will be plenty in the future.

The Arizona Water Banking Authority has given the city approval to pump from the ground CAP supplies that the authority had stored underground in the Tucson area in the past to prepare for shortages. It won't take much effort for the city to gain access to this water because it's now stored at one of the city's groundwater recharge facilities in the Avra Valley west of Tucson.

That facility, known as the Central Avra Valley Storage and Recovery Project, was put online back in the early 2000s to both store the city's CAP water underground for future use and to provide a convenient, safe way for the city to first recharge and then pump out its own CAP water for immediate delivery to homes and businesses.

But over the years, those groundwater recharge basins have also been increasingly used to store entities' surplus CAP water, including that owned by the water banking authority. The authority was created by state law to enable the underground storage of CAP supplies that cities and farms had no immediate use for, so the water could be saved for times of future shortages.

The 71,000 acre-feet in new CAP water the city is likely to order in 2027 is not only far less CAP water than it's ordered in recent years, it's also significantly less CAP water than the total demand for water from the homes and businesses served by Tucson Water.

Historically, Tucson Water customers have used close to 100,000 acre-feet a year, although this year their total use of drinking water will probably be less than 95,000 acre-feet, said Avery.

At this time, it's not certain exactly how much CAP water the city will order for 2027 — "it could be 70,000 or it could be 72,000," Avery said.

Leaving the extra Colorado River water in its Lake Mead reservoir is "vital for the state," even if the city has to pump out a few thousand acre-feet of its own stored CAP supplies, said Avery.

Tucson is voluntarily leaving 50,000 acre-feet next year in Lake Mead. The city will be compensated by the U.S. Bureau of Reclamation for leaving that water, by about $325 an acre-foot, or about $16.5 million total.

Besides that, Tucson will leave an additional 2,800 acre-feet to put towards a much larger, longer-term outlay of federal cash from Reclamation to build a new "advanced water purification" project on Tucson's northwest side to treat a small amount of wastewater from a Pima County sewage treatment plant to make it safe for people to drink. Overall, the city will get about $86 million for that project over a number of years.

Finally, as part of Reclamation's cutback in river water deliveries for next year, the city will lose close to another 20,000 or more acre-feet of CAP water without compensation. That's the loss that the Arizona Water Bank will make up for by allowing Tucson to pump out some of its stored water.

The 50,000 acre-feet that the city will leave in Lake Mead in return for compensation will be part of what state water officials across the Colorado River's Lower Basin states (Arizona, California and Nevada) hope will end up conserving 700,000 acre-feet over the next two years beyond what the federal cuts will require them to conserve.

Beyond that, the three states have set a goal to try to conserve a total of 1 million acre-feet in 2027 and 2028 beyond what they've already agreed to conserve, Avery said.

Saving this water is "vital to ensuring the most dire outcomes are avoided" to Lakes Mead and Powell and to the river itself, said Avery. The bureau's monthly forecasts have raised the real possibility of those reservoirs falling low enough that their accompanying dams won't be able to generate electricity.