Where Does All The Rainwater In LA County Go?

A lot of the rainfall we have had this past week will eventually reach our taps — roughly 25 years from now.

As of Friday, the L.A. County Department of Public Works reported capturing 1.2 billion gallons of water, enough to serve 30,000 people for a year. So what happens to that all that water once it's captured? Let's go through the process for going from stormwater to drinking water.

What happens to the captured water?

Stormwater is captured at the reservoirs and mountains, with the water allowed to flow through the dams, dam valves and channels like Tujunga Wash, Rio Hondo and San Gabriel River.

The collected stormwater first goes to a sediment trap, and then to spreading facilities in the county’s foothill areas.

There, the water seeps into the ground.

“It goes through the sands, gets clean, goes very deep into the ground, sometimes over two or three hundred feet,” said Mark Pestrella, public works director. “Eventually it makes its way to the groundwater table where we store our water.”

Purveyors then drill wells into the ground where the water is stored to capture and treat it before it makes its way through plumbing into homes.

“So every morning when you wake up and you turn the water in Los Angeles County from your faucet, you're actually drinking water from one of my reservoirs,” Pestrella said.

Some of that water is still being imported from the Colorado River and Northern California.

This process takes anywhere from 10 to 25 years and the timeframe depends on the soil type.

Why does LA County capture stormwater?

“This is easy because people might've heard the song, let's see, Joni Mitchell, was it? 'We paved over L.A. and made it a parking lot,’” he said.

With urbanization, Los Angeles County, Pestrella said, has become “hardscaped,” meaning “nothing can actually penetrate it.”

What the county is doing now is injecting water, rather than pulling it out or “unpaving LA,” he said.

“For instance, at the end of a cul de sac, we'll take a drill rig, and we will drill a hole very deep into the ground in the middle of the cul de sac, and then we'll put a big grate over it,” Pestrella said. “So all the water runs down, and it goes into this grate, and into this, drilled well. . . that well will actually send the water directly down into the earthen material and let it soak into the ground.”

With the approval of the L.A. County Water Plan, the county is set to increase stormwater capture by 2045.

While more water will be captured, residents are doing a great job with conservation, Pestrella said.

“We're using the same amount of water we've been using for 20 years, despite the population increase, and we attribute that directly to people conserving water at home,” he said.

The plan, he added, is to make imported water the last priority.