Arizona recycles more water than most Colorado River states, study finds

Yahoo

07-04-2025

Arizona is growing fast, but its water supplies are not, so to stretch every drop, cities capture and use water even after it runs down sink and shower drains.
The result: Arizonans reuse about half of all their wastewater, the second-highest rate of any Colorado River basin state, according to a new study from the University of California, Los Angeles.
And if all seven basin states reused as much of their wastewater as Arizona does, the researchers found that the states could recycle a combined 1.3 million acre-feet of water each year, roughly 10% of the Colorado River's average annual flow. The number doesn't account for any potential losses from reusing water that would otherwise flow back to the river, though the authors expect that number to be small.
Across the seven states, 27% of wastewater is recycled, according to researchers at UCLA's Institute of the Environment and Sustainability and the Natural Resources Defense Council.
'Even recycling 40% of our wastewater could make a dramatic difference, and we have two states already above 50% showing this is an entirely feasible solution,' said author Noah Garrison, a water researcher at the institute.
Recycled wastewater in Arizona irrigates golf courses and lawns, recharges aquifers and supplies the cooling systems at the Palo Verde Generating Station, the nuclear power plant that provides 27% of the power generated in the state. In total, reuse adds about 264,000 acre-feet of water to the state's supplies each year, based on 2022 data.
Reclaimed water represents around 5% of the state's overall water budget, according to a statement by the Arizona Department of Water Resources.
'Arizona has a strong history of water management and conservation success. Water reuse is becoming an increasingly important part of the state's overall water portfolio,' a spokesperson for the Arizona Department of Water Reuse said in a statement.
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The only Colorado River basin state that recycles more of its wastewater is Nevada, with a reuse rate of 85%. Las Vegas's overwhelming reliance on the Colorado River, combined with its location near Lake Mead, makes wastewater recycling more feasible there, according to Garrison and study co-author Mark Gold. Returning water to Lake Mead allows Nevada to stretch its small share of the river farther.
California followed Nevada with a 22% reuse rate, followed by New Mexico (18%) and the three other states in the Upper Colorado Basin (Colorado, Utah, and Wyoming), all with rates below 4%.
Garrison, Gold and their coauthors called hundreds of water districts in several states to find the numbers. Each state's rate is statewide, meaning they include some facilities that don't receive water from the Colorado River, but most of the largest cities in all seven states are connected to the river system in some way.
The study does not include one of Arizona's largest uses for its wastewater, the Tres Rios Wetlands, in its percentage. At Tres Rios, Phoenix rehabilitated wetlands that naturally filter effluent from its 91st Avenue Wastewater Treatment Plant. While an innovative project, the authors only included reused water that offsets water demand by sending wastewater straight to a human use (Tres Rios water ultimately flows back into the Salt River drainage).
'Tres Rios is such an amazing project, a nature-based solution,' Gold said in an interview. 'We're not saying that the use of recycled water for environmental purposes isn't there, but we're really trying to focus on what has an impact on water supply.'
The study included one of Arizona's largest uses for recycled wastewater, the cooling systems at the Palo Verde nuclear plant. Palo Verde uses a quarter of Arizona's recycled wastewater each year for its cooling systems. Though the authors included the power plant in their reuse percentage, they also questioned the real benefits of such water-intensive energy production in Arizona.
'The recycled water consumed as cooling water by the Palo Verde plant also raises significant questions as to the sustainability of this use,' the study reads.
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Arizona could see even more water-recycling projects soon. The authors note that Phoenix is working on water reuse projects at its 91st Avenue and Cave Creek wastewater facilities and that Palo Verde is exploring the possibility of a dry cooling system. Arizona also approved rules for advanced wastewater purification for potable reuse in March, a major step in advancing wastewater recycling in the state.
Arizona Public Service, the primary stakeholder in Palo Verde, did not immediately respond to a request for comment.
While Arizona received high marks for its wastewater recycling, the authors said the state does not have easily accessible data on its wastewater management. The authors had to directly call wastewater treatment facilities for much of their Arizona data. At some of those facilities, operators couldn't quantify where much of their reused water went, instead relying on anecdotes, according to the authors.
The Arizona Department of Water Resources and the Arizona Department of Environmental Quality confirmed in a joint statement that they do not collect comprehensive data on the volume of the state's wastewater reuse, pointing to individual utilities as a direct source for that information. An ADEQ spokesperson noted that quantifying reuse is a challenging task, especially given that water can be reused multiple times.
Arizona is not alone in having a tough information landscape around wastewater reuse. California is the only state in the basin with a compiled information portal on the subject, and the authors said they struggled to find information in other states as well.
With better data and more encouragement from the federal government, the authors hope that wastewater recycling can make a serious dent in shortages on the Colorado River.
'We absolutely need to be developing these additional sources of water and investing in them now,' Garrison said.
Austin Corona covers environmental issues for The Arizona Republic and azcentral. Send tips or questions to [e-mail]
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This article originally appeared on Arizona Republic: Arizona reuses half of its wastewater, more than other western states