How Los Angeles Is Turning Stormwater Into Future Drinking Water
California is forecast to be ground zero for the El Niño moisture along the West Coast this winter. State officials are hoping to take advantage of this boon by saving water for use during the next drought. Here is a look at how the state is planning to harvest water during the predicted wet winter for use in the future.
California Looks to Harvest Incoming Moisture Surge
It was just a few years ago that California was in the throes of a severe drought. The moisture machine has picked up over the last several months, helping to bring reservoir water levels back up to near capacity.
According to California Water Watch, Ventura County's Lake Casitas was 94% full last week, while reservoirs across the state are averaging about 104% of the norm for this time of the year. The latest long-range forecast is growing increasingly confident that the Golden State will bear the brunt of a parade of potent storms roaring in from the Pacific this winter. This persistent stream of moisture will likely send the reservoir water levels climbing.
The challenge facing the state now is how to balance the task of releasing just enough water from reservoirs to prevent them from overflowing while still keeping as much as possible for use during the next drought. If not enough water is released, the reservoir could overflow and trigger flooding. If too much water is released, there is the risk that it will not be replenished.
Marty Ralph, director of the Center for Western Weather and Water Extremes at Scripps Institution of Oceanography, explained how California reservoir operators released too much water in 2013, leading to an extreme shortage down the road. Ralph detailed that officials released water in preparation for a major storm; however, that moisture never arrived. He described how “no more storms came for the rest of the winter, and that unnecessary water release left the whole watershed in a terrible situation that summer.”
A strategy already being used in Los Angeles County could serve as a blueprint for similar initiatives across the Golden State. The most populated county in the state operates 27 spreading grounds designed to soak up stormwater rather than diverting it toward the ocean. Because these basins are built over porous soil, the water is retrieved and collected in underground storage areas.
Los Angeles County was able to capture about 120 billion gallons of stormwater during the 2025 - 2026 wet season. This translated to about ten times the volume captured the previous year. According to county officials, this amount of water is enough to meet the needs of about 3 million residents.
Similar efforts have been launched in California's Central Valley. However, experts caution that storing this water underground has limits. For example, the soil can only absorb so much water when the moisture is coming down at a fast clip. The process also requires the right soil composition, diversion infrastructure, and enough groundwater capacity to capture and store the water.
New Forecast Tools Will Play a Role in Decision Making
Climate experts are also hoping to lean on increasingly accurate weather forecasts to guide their decisions about California's water use. A tool known as the Forecast-Informed Reservoir Operations (FIRO) uses high-resolution forecasts to decide when to hold onto reservoir water and when to release it.
For instance, officials can create more room for the predicted runoff when the tool shows that an atmospheric river is headed that way. Conversely, if the flood threat is low, they will feel more confident in retaining the water.
A recent study from Scripps Institution of Oceanography predicted that using FIRO more when deciding when to release water across 20 of the state's major reservoirs would yield an additional retention of 100 billion to 160 billion gallons of water each year.
State officials are hopeful that all of these strategies will help them to find the right balance in making room for the predicted surge of moisture while preserving as much as possible for the next drought. As the impacts of climate change become more entrenched, these innovative strategies are becoming more necessary.
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