California used less water than officials estimated between 2000 and 2020, according to a new report.
While the findings call into question the accuracy of long-term water demand forecasts and could have a knock-on effect on costs borne by consumers, the news that overall water demand is lower than predicted is positive for the state and its regular fight against drought, experts told Live Science.
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Water management has long been an important issue in California, which has approximately 8.5 million acres (3.4 million hectares) of irrigated agricultural land. Crops such as grapes, almonds and pistachios support the state’s economy and create hundreds of thousands of jobs. Agriculture accounts for approximately 40% of California’s average annual water use, with 10% used by local communities and 50% returned to the environment.
However, the state’s supply of this precious resource is often at risk due to prolonged droughts, long-term depletion of groundwater supplies, and population growth.
Although water use projections generally assume that it will increase with population growth, California has introduced many water conservation measures. So to examine how projections compare to actual usage, Johanna Capone, a Virginia Tech graduate student, and Landon Marston, an associate professor in the Virginia Tech Department of Civil and Environmental Engineering, evaluated the state’s urban water management plans prepared every five years by California’s 61 municipal water suppliers from 2000 to 2020.
They found that water suppliers consistently overestimate future demand by an average of 25% in five-year forecasts and by 74% in 20-year forecasts.
This overestimation primarily stems from projections of how much water each person will use, rather than assumptions about population growth, Capone and Marston report in a study published Nov. 21, 2025, in the journal Water Resources Research. Although suppliers generally expected per capita demand to remain stable or increase, actual per capita water demand decreased by 1.9% annually between 2000 and 2020. This means that water demand is no longer precisely correlated with population growth.
“I think the overall conclusion is that California has done a great job of reducing demand,” Capone told Live Science. “The nation is clearly on the right path.”
This finding is consistent with the results of other similar studies.
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“This trend is consistent with what I’ve seen in California as well as other regions,” Cooley said. She is also the author of a 2020 study that showed declines in per capita water use at 10 California water utilities between 2000 and 2015.
She said water use and population growth had become increasingly decoupled, so the two could no longer be considered linked.
“This study showed, as other studies have shown, that we can grow and support economic development by using less water. Efficiency is a key strategy to help do that,” Cooley said.
Capone attributes the reduction in water use to water-related initiatives, education campaigns and financial incentives such as rebates for replacing lawns with drought-tolerant landscaping, promoted by state policies such as the California Green Building Code and the Model Water Efficient Landscaping Ordinance.
Those regulations require new developments to use water-efficient versions of equipment such as toilets, showerheads, sprinklers and washing machines, Cooley said. It also helps when older versions of these devices are replaced by newer, more efficient models. New initiatives also address outdoor water use by limiting the amount of grass and other plants that require large amounts of water, she said.
“As these communities get denser and the lawns get smaller, the water demand naturally goes down in the same way that water demand goes down as buildings become more efficient,” Capone said.
But water suppliers need to make their forecasts more accurate to account for changes in water efficiency incentives, she said.
“It’s a difficult balance because people may perceive that their water needs are decreasing and, hopefully, they may not want to take advantage of this situation to increase the amount of watering on their lawns,” Capone said. “However, it is important to try to be as accurate and realistic as possible, because if water demand is over-forecast, water suppliers may be hit with additional costs that can be passed on to customers.”
That may require purchasing additional water supplies or building new water supply and treatment infrastructure, she said.
The study results do not mean California’s water supply challenges are over. “California remains a water supply problem, even though water use is decreasing as droughts become more intense and more frequent due to climate change,” Cooley said.
Wet years can help replenish the groundwater reserves California relies on, but water demand management is what ensures there’s enough water in reservoirs and aquifers for long periods of time so the state doesn’t have to apply its most severe water use restrictions when drought returns, Cooley said.
An analysis by the Metropolitan Water District of Southern California, which serves about 19 million people, found that without the district’s water efficiency efforts over the past 30 years, the region’s reservoirs would have run dry three times during that period.
“The key to managing water demand is to be collectively resilient and prepared for whatever the environment may throw at us,” Capone said.
One of the biggest challenges is continuing to reduce water usage as buildings become more efficient and lawns get smaller.
From 2000 to 2020, per capita water demand decreased by an average of 1.9% per year, but a closer look at the Capone and Marston paper shows that per capita water demand decreased by approximately 2.6% per year from 2000 to 2015, but increased by an average of 0.29% per year from 2015 to 2020. These numbers raise questions about whether efforts to manage water demand have reached a plateau.
If so, a different focus may be needed to continue reducing water usage. “When you think of water conservation, you think of ads like ‘brush your teeth without running water’ or ‘soften your teeth if they turn yellow,’ but this goes beyond just the home,” Capone said.
She says it’s important to look at other places where water is being used and see if building codes or landscaping can reduce its use.
The potential for water savings across the United States is enormous. A November study from the Pacific Institute, co-authored by Cooley, found that improving water efficiency in U.S. homes and businesses and reducing leakage in distribution systems could save 14 million to 34.1 million acre-feet per year, or 12.5 billion to 30.4 billion gallons (115 billion liters) per day, and that even basic upgrades to meet existing standards could reduce water use nationwide by a quarter.
“There are many opportunities to reduce water use and make our communities more sustainable and resilient,” Cooley said.
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