TUCSON — An $86.7 million agreement with the Bureau of Reclamation has put Tucson on track to build a plant to treat wastewater to drinking water standards by late 2031.
The federal agency will pay for constructing an advanced water purification facility northwest of the city in exchange for Tucson leaving 56,000 acre-feet of Colorado River water behind Lake Mead over the next 10 years.
“This project is not about infrastructure, it’s about protecting a shared resource,” said Councilwoman Nikki McMillen Lee who represented the mayor and council as the bureau and city officials signed the agreement Wednesday at Sweetwater Wetlands Park.
Overallocated and gripped by drought, the Colorado River system is under strain, and its shrinking flow threatens the everyday water and energy supply of seven states and 30 tribes, as well as the health of the basins’ ecosystems.
The agreement was part of a larger $257.6 million investment in Arizona from the Department of Interior’s Lower Colorado River Basin System Conservation and Efficiency Program, funded through the Bipartisan Infrastructure Law.
On Wednesday, the Town of Gilbert also signed a nearly $17 million agreement for investments in 27,943 advanced metering infrastructure radios and structures to increase aquifer recharge at the town’s riparian reserve with reclaimed water. They will conserve 8,500 acre-feet of water over the next 10 years.
“These meters will provide real-time data that allows us to pinpoint and address leaks much faster than current technology does, and thus reduce water loss,” Gilbert Mayor Scott Anderson said Wednesday. “In 2023 alone, within a portion of our service area, Gilbert saved 43 million gallons by alerting customers to leaks thanks to AMI data.”
Tucson’s treatment plant would stretch the city’s water resources. Treating sewage and purifying it to drinking water standards is already done on a large scale in California, Texas and Colorado, as well as cities around the world like Abu Dhabi and Singapore.
“Tucson won’t be unique in the journey. We have the city of Phoenix and Scottsdale already moving towards advanced water purification programs and now Tucson will join them over the next couple of years,” said Tucson Water Director John Kmiec. “This is the next step in our water resource planning and water reliability for the community.”
The initiative to build the plant was part of Tucson’s recycled water strategy and the city’s One Water plan, which considers surface water, recycled water, groundwater and stormwater as equally important in Tucson’s water portfolio.
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New technology is already in use
Arizona has already gone through a long process to make advanced water purification, also known as direct potable reuse, a reality. Two years ago, the Arizona Department of Environmental Quality began creating a regulatory framework and issued the draft rules last year. They haven’t been finalized and adopted yet.
Phoenix has two projects that could treat reclaimed water to potable standards. The city is working on rehabilitating the Cave Creek Water Reclamation plant, which will treat 8 million gallons of wastewater per day. The city expects to finish construction of the reclamation facility in early 2027 and could add new technologies and processes the year after to make the water drinkable for human use.
Phoenix is also in the early planning stages of a plant that could purify 80 million gallons per day and serve other cities like Mesa, Scottsdale, Glendale and Gilbert. The city is still working with partners on a feasibility study and water exchange agreements. Construction of the 91st Avenue Regional Advanced Water Treatment facility, southwest of downtown, is anticipated to start in five years, according to a spokesperson for the Phoenix Water Services Department.
Scottsdale was the first to build a pilot program for advanced water purification at its advanced water treatment facility, which treats 20 million gallons of recycled water a day to potable quality using ozonation, membrane ultrafiltration, reverse osmosis and ultraviolet disinfection. The city is not sending the purified water to customers yet.
Until ADEQ regulations are official, water utilities cannot apply for permits to send water from these plants directly to customers as drinking water.
Tucson will also have to go through a yearslong process to design, build and get permits for the plant.
The plant will be built near the Tres Rios water reclamation facility, which currently releases about 30 million gallons of highly treated effluent into the Santa Cruz River, reviving the river ecosystem. Tucson Water will take a portion of what is now being discharged into the river and purify it to supplement the drinking water system with about 2.5 million gallons a day.
“All the technology is essentially already developed because there is advanced water purification happening around the world,” said Kmiec. “But what we will be doing in the planning stages for the next couple of years with the Arizona Department of Environmental Quality is we will be looking at the current recycled water quality that Pima County’s Tres Rios produces and then we will be designing a purification process around that.”
The new water source will support demands northwest of the city, where the utility had to shut down dozens of wells due to contamination by PFAS, also known as forever chemicals. The 2.5 million gallons a day coming from the plant will help offset those impacts with a “reliable supply of high-purity water,” Kmiec said.
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Less river water to bank on
Starting in 2026 Tucson will be ordering less Colorado River water. The city will decide how much it reduces its order every year to achieve a reduction of 56,000 acre-feet of water by 2035.
If evenly split across a decade, these reductions would amount to less than 4% of the Colorado River water Tucson receives in a year.
“The city’s current Colorado River water allotment is at 144,199 acre-feet, but our community only consumes about 100,000 acre-feet a year,” said Kmiec.
“We’ve been in an excess pattern where we’ve been banking water for the future in Avra Valley, in our recharge facilities, so making these small cuts into our allotment still doesn’t dip into the annual use of the water supply for Tucsonans,” Kmiec said. “It’s just a little less water that we’re putting in the aquifer for future use.”
Two years ago the city made a bigger voluntary reduction, compensated at $400 per acre-foot. Amendments to that agreement for 2026 will bring Tucson’s conservation effort to a total of 160,000 acre-feet of water.
The reductions also barely dip into the Colorado River’s increasing conservation needs. Seven states and 30 tribes in the Colorado River basin are stuck in negotiations over how they will split painful water reductions in the future, as the shortage-sharing guidelines that allowed for past water cuts come closer to expiration.
The term of U.S. Bureau of Reclamation Commissioner Camille Calimlim Touton is coming to an end on Monday, but the agency is on track to meet the deadline, she said Wednesday in Tucson.
“We’ve been in active discussions and the Bureau of Reclamation will continue to be in active discussions with the basin states, with the 30 tribes, as well as parallel agreements with the country of Mexico,” she said.
“There needs to be an agreement by August of 2026,” Touton said. “We’ve put in the steps to ensure that we meet that deadline and I know that all of the groups, all of the states are talking to ensure we meet those operating criteria. By when we need them.”
Clara Migoya covers agriculture and water issues for The Arizona Republic and azcentral. Send tips or questions to [email protected].
