California isn’t recycling nearly enough water, according to a new report by UCLA researchers, who say the state should treat and reuse more wastewater to help address the Colorado River’s chronic shortages.
Analyzing data for large sewage treatment plants in seven states that rely on Colorado River water, the researchers found California is recycling only 22% of its treated wastewater. That’s far behind the country’s driest two states: Nevada, which is recycling 85% of its wastewater, and Arizona, which is reusing 52%.
The report, based on 2022 data, found other states in the Colorado River Basin are trailing, with New Mexico recycling 18%, Colorado 3.6%, Wyoming 3.3% and Utah less than 1%.
The researchers said that California and other states, with support from the federal government, should scale up investments in water recycling facilities to help as the region faces demands to dramatically reduce water use in order to prevent the river’s reservoirs from falling to critically low levels. They said the Southwest needs to prioritize water recycling to adapt as droughts grow more intense and long-lasting with global warming.
“We’re facing a hotter, drier future and we need to pursue water recycling aggressively if we’re going to ensure a sustainable, resilient water supply,” said Noah Garrison, a water researcher at UCLA’s Institute of the Environment and Sustainability.
“There is huge opportunity here,” Garrison said. “We need to create these new and resilient, reliable sources of water.”
The study shows that across the seven states, an average of 26% of municipal wastewater is being recycled.
If California and other states were to pursue targets of recycling 40% or 50% of their wastewater, the researchers said, that would go a long way toward addressing the river’s gap between supply and demand. If every state achieved even 30%, they calculated, that would generate more than 450,000 acre-feet of water annually — almost as much as the total annual usage of Los Angeles.
“These modest gains in water reuse could make an enormous difference on the Colorado,” said co-author Mark Gold, a UCLA adjunct professor and director of water scarcity solutions at the Natural Resources Defense Council.
The biggest potential lies in California, which uses more Colorado River water than any other state. The water flows in aqueducts and canals to desert farmlands and cities from Palm Springs to San Diego.
Some of Southern California’s urban wastewater is treated and reused to irrigate golf courses and parks, while Orange County has a system that purifies wastewater and puts it into the groundwater basin for use as drinking water.
Other treated effluent is discharged into rivers or the ocean.
Penstocks at the Gene Pumping Plant, near Lake Havasu, transport Colorado River water to Southern California.
(Brian van der Brug / Los Angeles Times)
The researchers compiled statewide data for all seven states in the Colorado River Basin, including areas that rely on the river as well as other areas that do not.
In coastal Southern California, from Ventura County to San Diego County, 29% of wastewater is currently recycled, the researchers said. According to state data, building three large planned water recycling projects would enable the region to reuse more than 56%.
Once fully built, these three facilities, planned by San Diego, Los Angeles and the Metropolitan Water District of Southern California, would dramatically increase local water supplies. The total cost for the three projects and new water distribution systems could exceed $25 billion, the report said.
Although the costs will be substantial, building these projects should be viewed as vital infrastructure improvements, Gold said.
“We’re clearly not managing water in a sustainable manner, and recycled water is just so critical as a way to do that,” Gold said.
The researchers said that major state and federal investments will be necessary for the work, and that it should be undertaken with urgency.
The Colorado River provides water for cities from Denver to Los Angeles, 30 Native tribes and farming communities from the Rocky Mountains to northern Mexico.
The river has long been overused, and its reservoirs have declined dramatically amid persistent dry conditions since 2000. The average flow of the river has shrunk about 20% since 2000, and scientists have estimated that roughly half of that decline has been caused by global warming driven by the burning of fossil fuels.
The decline in flow is projected to worsen as temperatures rise.
The All-American Canal delivers Colorado River water into California’s Imperial County.
(Carolyn Cole / Los Angeles Times)
“We can’t afford not to move forward with water recycling because of the importance of reliability and climate resilience,” Gold said.
The river’s average difference between supply and demand has been estimated to be between 2 million acre-feet and 4 million acre-feet annually, Gold said. A large portion of this could be offset by recycling more water.
“But this can’t happen without major federal and state investments,” Gold said.
The researchers called for the federal Environmental Protection Agency to develop water reuse goals, and for state governments to commit to targets — such as 30%, 40% or 50% — and work with other agencies to secure funding. They also said states need to collect better data on water recycling.
Several states lacked that basic information, and researchers had to call treatment plants one by one to learn how much water is being treated and reused.
“The lack of adequate data is a significant barrier,” Garrison said. “The fact that most of the states have little idea what’s happening is a real and growing problem.”
The researchers said California has the nation’s most comprehensive regulations on recycled water and also leads other states in tracking data on reuse. They said the state adopted ambitious water recycling goals in 2009 but those targets were effectively abandoned under a state strategy adopted in 2022.
“The real problem is that in 15 years, we’ve made almost no progress,” Garrison said. “It’s really time for California to start investing much more heavily in this as a solution, particularly given the uncertainty around Colorado River Basin water.”
Over the last few years, the State Water Resources Control Board has provided $1.4 billion for projects that will produce an additional 125,000 acre-feet of recycled water annually, said E. Joaquin Esquivel, the board’s chair.
“Increasing recycled water use is a top priority for the state and a key part of Gov. Newsom’s strategy to buffer the anticipated loss of 10% of our water supplies by 2040 due to hotter, drier conditions,” Esquivel said in an email.
He said that although there has been tremendous progress by the state and Southern California agencies in recent years, “continued investment and planning is critical to leverage the full potential of recycled water and simultaneously reduce reliance on the Colorado River.”
