Research shows that enforced water-use reductions increased California’s water efficiency

After drought-stricken California rescinded a year of mandatory water-use cuts that were effective in 2015 and 2016, urban water use crept back up somewhat, but the overall lasting effect was more permanent. Golden State, University of California, Riverside, study finds .

Published Tuesday, April 25 in the magazine Water resources researchThe UCR study found that water use by 2019 was still lower than it was in 2013, thanks in large part to changes in water use by larger water users.

the then-government’s water-cutting mandate in 2015. Researchers found that Jerry Brown also motivated Californians to develop better water-saving habits, such as watering lawns and gardens during the cooler morning hours when less water is lost to evaporation. The study analyzed about half a billion records of water usage data per hour.

Most of the permanent savings in water have come from discerning water users, who get a greater return on investments in water efficiency.

“Higher-income water users tend to be wealthier and have more,” said the study’s lead author, Mehdi Nemati, assistant professor of water resource economics at UCLA’s School of Public Policy. “They’ve embraced the technology one way or another, and their recovery on water use is much lower than on low usage.”

Low-income water users—people with lower incomes and smaller yards—tend to let their lawns turn brown during the period of water cutting mandates. So, when the mandate was lifted, those users resumed irrigating their lawns, which contributed to a 13% to 15% increase in water use over the term — but water use was still lower in 2019 than in 2013.

The data provides new insights into Governor Brown’s controversial executive order in 2015 that required state water providers to cut urban water use in the state by 25% after three years of worsening drought. To achieve this goal, water providers in individual urban areas, such as city utilities and water districts, had to reduce water consumption by 4% to 36%, depending on what water conservation measures each entity had already implemented. Brown’s term was in effect from June 2015 to May 2016.

The UCR researchers focused on accurate data from the Northern California water utility that serves about 70,000 people and were able to extrapolate trends to the entire state with data from an ongoing statewide study, Nemati said.

The Northern California utility was required to reduce its water supply by 32%. To do so, it offered discounts to replace grassy lawns with drought-tolerant landscaping, to upgrade irrigation systems, and for residences and businesses to install more water-efficient toilets and washing machines, among other water-conversation measures.

Significantly, the facility also banned irrigation between the hours of 10 a.m. and 10 p.m., when high outdoor temperatures would increase irrigation water loss from evaporation.

“In line with best water use practices, people moved to earlier irrigation hours, and continued to do so after the mandate was lifted,” Nemati said. “This was one of the results with the hourly water usage data.”

Nemati warned that in the future it will be more difficult to achieve reductions in water use because many higher-level water users have already invested in water efficiency.

“It’s good for water agencies to know that we’ve already gotten rid of most of our low-hanging fruit,” he said.