California says more wastewater should be treated and reused to address the chronic shortage of the Colorado River, according to a new report by UCLA researchers.
Analyzing data from large sewage treatment plants in seven states that rely on the waters of the Colorado River, researchers found that California recycles only 22% of the wastewater that has been treated. It is far behind in the two driest states in the country. Nevada recycles 85% of its wastewater, while Arizona recycles 52%.
Based on data from 2022, other states in the Colorado River Basin are in the late stages, with New Mexico recycling of 18%, Colorado 3.6%, Wyoming 3.3%, and Utah under 1%.
With federal support, researchers said California and other states should expand their investment in water recycling facilities as the region faces demands to prevent river reservoirs from falling. They said the southwest needs to prioritize water recycling to adapt as a global warming drought.
“We are facing a hotter and drier future. We need to actively pursue water recycling to ensure a sustainable and resilient water supply.”
“There’s a huge opportunity here,” Garrison said. “We need to create these new, resilient, reliable water sources.”
The study shows that an average of 26% of city wastewater is recycled in seven states.
If California and other states pursue a goal of recycling 40 or 50% of wastewater, researchers said it would go a long way in addressing the river gap between supply and demand. If all states achieve even 30%, they calculate and produce more than 450,000 acre feet of water each year. This is roughly the same as the total annual usage in Los Angeles.
“The modest benefits of reusing water can make a big difference for Colorado,” said Mark Gold, an auxiliary professor at UCLA and director of water rarity solutions at the Natural Resources Defense Council.
The greatest potential lies in California, which uses more Colorado River water than any other state. The water flows through the aqueducts, canals and cities from Palm Springs to San Diego.
Some of Southern California’s urban wastewater is irrigating golf courses and parks, but Orange County has a system in which it places it in groundwater basins for use as drinking water.
Other treated wastewater.
The researchers compiled statewide data for all seven states in the Colorado River Basin. This does not include areas that depend on rivers or are not.
On the Southern California coast from Ventura County to San Diego County, 29% of wastewater is now recycled, researchers said. The construction of three large-scale planned water recycling projects will allow the area to reuse more than 56%, according to state data.
Once fully constructed, these three facilities dramatically increase local water supply. The total cost of the three projects and the new water distribution system could exceed $25 billion, according to the report.
The cost is substantial, but building these projects should be seen as a critical infrastructure improvement, Gold said.
“We obviously don’t control water in a sustainable way, and recycled water is a very important way to do that,” Gold said.
The researchers said major state and federal investments are needed for work, and that should be made urgently.
The Colorado River provides water to cities from Denver to Los Angeles, 30 native tribes and agricultural communities from the Rocky Mountains to northern Mexico.
The river has been in use for a long time, and its reservoirs have declined dramatically in the persistent arid conditions since 2000. The average river flow has been shrinking by about 20% since 2000, and scientists estimate that about half of that decline is driven by fossil fuel burning.
The flow drop is predicted to worsen as temperatures increase.
“Due to the importance of reliability and climate resilience, water recycling cannot go ahead,” Gold said.
The average difference between supply and demand on the river is estimated to be between 2 million and 4 million acre feet a year, Gold said. Most of this can be offset by recycling more water.
“But this could not happen without major federal and state investments,” Gold said.
Researchers asked the Federal Environmental Protection Agency to develop water reuse targets and state governments to commit to targets such as 30%, 40%, or 50%, and work with other agencies to secure funding. They also said the state needs to collect better data on water recycling.
Some states lack basic information, and researchers had to call the therapeutic plants one by one to learn how much they would be processed and reused.
“The lack of proper data is a major barrier,” Garrison said. “The fact that most states have little thought into what is going on is a realistic and growing issue.”
Researchers said California has a nation on recycled water, and other states are leading the way in tracking data on reuse. They said the state adopted ambitious water recycling targets in 2009, but these targets were effectively abandoned.
“The real problem is that there’s little progress in 15 years,” Garrison said. “It’s time for California to start investing in this with more investments as a solution, especially given the uncertainty surrounding the waters of the Colorado River Basin.”
Over the past few years, the state’s Water Resources Management Board has provided $1.4 billion for projects that produce 125,000 acre feet of recycled water each year.
“Increasing the use of recycled water is a top priority for the state and is an important part of our key strategy to mitigate the expected 10% losses by 2040.
He said that while significant advances have been made by state and Southern California agencies in recent years, “continuous investment and planning are important to maximize the potential of recycled water and at the same time to reduce reliance on the Colorado River.”
