Historic rain in Los Angeles leads to billions of gallons of rainwater collected

After so much rain has fallen in Southern California this week, we wanted to know how much is saved for future use and how it's done. For that, we turned to the Los Angeles County Department of Public Works.

Mark Pestrella is the Director of the LA County DPW. To him, capturing rain water is like saving money in the bank. Rain water capture happens at dams, like Big Tujunga or Pacoima, to name a couple. When it rains, Pestrella says, "each water drop that travels across the land" ends up in rivers, lakes and streams" On it's way there, "we capture it in our dams, and we store the water behind the dams."

Pestrella says the county has captured 21 billion gallons of water so far in 2024, which is "enough to serve 517,000 people for a year." Just from this week's storm alone, the county captured 11.4 billion gallons of water, enough for 280,000 residents.

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So how do we get the water once it's behind the dams? The water released from dams goes into spreading grounds, of which there are 27 in LA County. 

"It's a natural system that soaks into the ground because we're sitting on top of a bunch of gravel that absorbs water very nicely," said Pestrella.

The water soaks into the ground, it gets cleansed and absorbed into the groundwater basin, about 300 feet deep. Then, that water is pumped into wells, treated again, and "we put it into the plumbing in people's homes, and eventually that water that fell in the mountains is coming out of your tap," Pestrella said.

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Water that can't be saved, like much of what we see in the LA River, goes into the ocean. Were there no LA River, Pestrella said, our neighborhoods would be a big lake just as they were before the LA River was built. In 1938, Pestrella said, "we had a lake that spanned from Orange County all the way to LA County. There's talk people had to use boats to get from Long Beach to downtown LA."

The San Gabriel River doesn't have a lot of concrete like the LA River does, so a lot of water is saved there. From this storm alone, Pestrella said, the county has captured about 90% of the water that fell, which Pestrella said is "at least a third of the drinking supply for LA County on an annual basis."