Billions of gallons of water have fallen on Los Angeles County since last week. And much of that kept right on going — out into storm drains, lost to the sea. Couldn’t we actually use that water?

Yes, and we do. Southern California water managers want to use more of it. The city of Los Angeles has a goal of increasing its storm water supplies to 25,000 acre feet a year within 20 years – essentially doubling current supplies.

Some people and organizations pursue even more aggressive storm water capture plans to see how Southern California could use existing strategies to go even further.

The main thing storm water experts said, over and over: We need to think about water holistically.

Various public agencies have authority over water, and they serve different purposes. Some treat water as a supply to be brought to people; others treat it as something polluted, that should be carried away. “And that’s something we can’t afford to have going forward,” says Noah Garrison with UCLA's Institute of the Environment and Sustainability.

Ways we capture rain right now:

1. Spreading grounds

These are enormous depressions in the ground, the size of soccer fields, into which Los Angeles County Public Works and the Los Angeles Department of Water and Power send water. “We basically fill these basins full of water, and then that water percolates. Almost like a drip coffee maker,” DWP’s Marty Adams told KPCC. “Any contaminants that you’d see in off the street, if it’s bacteria, anything like that, all gets captured in the first few feet of soil. And so the water’s very clean as it travels, like a natural filter."

2. Cisterns and rain barrels

These are man-made ways to do the same thing. Water flowing off a roof can go straight into a rain barrel, for example. And at TreePeople’s Coldwater Canyon Park, by Friday, Dec. 12, they had collected 40,000 gallons of water during one storm in a massive cistern designed to collect water from the parking lot, off the roof of a building there, and straight through the ground.

TreePeople’s cistern is 70 feet wide, 8 feet deep, buried underground, and it can hold 216,000 gallons of water – enough to help the park live off the grid during wet years. In dry times, cistern water keeps struggling trees in the park alive.

And during in-between years, Lipkis says water can help firefighters in an emergency – when regular water pressure is low. “This isn’t to scare people, but we’re living in a very risky environment,” he says. “What resilience and sustainability means is, looking ahead, seeing where we’re at risk connecting dots so that we have solutions at the ready.”

3. Low impact development principles

These support the capture and filtration of water as close to where it falls as possible. They’re included in regional and city regulations, and encourage features like bioswales, drainage courses with sloped sides that capture runoff.

Schools and public parks often find funding to put these principles into practice. So does the Amigos de los Rios, whose director, Claire Robinson, says the group imagines an "emerald necklace" along the Rio Hondo and San Gabriel Rivers, linking east Los Angeles County communities to mountains and rivers to the west.

OK, we’re only sort of doing this one:

4. Green roofs

These are one specific kind of a low-impact development design with multiple benefits, but they're far less popular in Southern California than they are in cities where rules encourage them, like Toronto, Washington, Chicago and Portland, Ore. (Los Angeles, not so much.)

UCLA's Garrison hopes that will change. "They can capture and retain up to 50 percent of rainfall in an average year," he says. "That’s water that’s not flowing off of paved surfaces, picking up pollution, and carrying it to our waterways."

Large green roof examples are few and far between in L.A. County. UCLA's Court of Sciences Student Center serves up Subway sandwiches, Yoshinoya beef bowls and other food down below, and 7,000 feet of green-roof seating above.

The Los Angeles Museum of the Holocaust features 12,700 feet of green roof, 2 feet thick, which helps insulate the building tucked into the side of Pan Pacific Park.

And the one we’re not doing yet:

5. Networked water storage

This would rely on technology like microchips to manage water stored diffusely, in multiple locations, over a large area of land. “Just like you can imagine network hard drives, and music sharing, now it’s networked tanks, and water sharing,” says TreePeople's Lipkis. Networked storage could manage water better to minimize flooding and pollution, and maximize supplies. "It’ll tell you if [the tank's] full, and chips are getting so smart they could be monitoring water quality in your tank as well," he says.

Lipkis, Garrison and Robinson all emphasize that these stormwater capture solutions rely on current technology, as well as past practices.

Amigo de los Rios' vision of an "emerald necklace" is inspired by Frederick Law Olmstead, whose Olmstead-Bartholomew plan never got to take shape the way a similar plan did in Boston.

Cisterns go back to ancient Arabia, even though Romans get credit for their widespread use.

For her part, Robinson's inspired by the Roman philosopher Lucretius. "He talked all about water and it was personified as the goddess Aphrodite," she says, referring to De Rerum Natura. "It talked about how water wins without really fighting. So I love the idea that if we were guided by water we would be a totally different culture."

Robinson and others say the necessity of drought might bring that world into existence sooner than we think.