Newswise —
A study by the University of California, Riverside, found that after California ended mandatory water-use cuts in 2015 and 2016, urban water use increased somewhat, but the state remained more water-conscious overall. This means that even though people started using more water again, they were still mindful of water conservation and continued to save water in the long run.
The University of California, Riverside study was published in the Water Resources Research journal on Tuesday, April 25th. The study found that by 2019, water use in California was still lower than it was in 2013. This was mostly due to changes in water use by larger water users.
When then-Governor Jerry Brown imposed a water-reduction mandate in 2015, it also encouraged Californians to develop better water-saving habits, like watering their lawns and gardens during cooler morning hours when less water evaporates. The researchers analyzed about 500 million records of hourly water use data to reach their conclusions.
Most of the permanent water savings came from higher-end water users, who get a greater return from investments in water efficiency.
According to Mehdi Nemati, the lead author of the study and an assistant professor of water resources economics at UCR’s School of Public Policy, wealthier people with larger properties tend to use more water. However, the study found that these individuals adopted technology and changed their water usage habits, resulting in a smaller rebound in water usage compared to those with lower water usage.
During the water-cut mandate period, lower-end water users with less income and smaller yards tended to let their lawns go brown. When the mandate was lifted, these users started watering their lawns again, which led to a 13-15% increase in water use compared to the mandate period. However, even though the mandate was lifted, water use in 2019 was still lower than in 2013.
This study gives us more information about what happened after California's governor, Jerry Brown, told water providers to reduce the amount of water used by people living in cities by 25% in 2015. The study found that the mandate helped to reduce overall water use in the state, especially among larger water users who tended to be wealthier and had bigger properties. Even after the mandate was lifted, people continued to use less water than before.
The UCR researchers focused on granular data from a water utility in Northern California that serves about 70,000 people and were able to extrapolate the trends to the entire state with data from an ongoing statewide study, Nemati said.
The Northern California utility had to decrease its water deliveries by 32% as part of the mandate. To achieve this, the utility offered incentives such as rebates for residents and businesses to replace grass lawns with drought-resistant landscapes, upgrade irrigation systems, and install water-efficient toilets and washing machines, among other measures to save water.
Significantly, the utility also banned watering between the hours of 10 a.m. and 10 p.m., when higher temperatures outdoors increase the loss of irrigation water from evaporation.
According to Nemati, people followed the best practices of watering their lawns and gardens during cooler morning hours even after the water mandate was lifted. This was revealed as one of the findings from the hourly water usage data.
Nemati cautioned that it would be more difficult in the future to achieve water-use reductions because so many higher-end water users have already invested in water efficiency.
“It is useful for the water agencies to know that we already got rid of most of our low-hanging fruit,” he said.
The study, called "Residential Water Conservation and the Rebound Effect: A Temporal Decomposition," was written by Mehdi Nemati, Dat Tran, and Kurt Schwabe from the University of California, Riverside’s School of Public Policy.
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