DAVID GREENE, HOST:
Now a radical idea about changing the relationship between cities and water. We're really talking about the city as a sponge. It's part of the NPR Cities Project.
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UNIDENTIFIED WOMAN #1: Becoming world-class city.
UNIDENTIFIED MAN #1: More unified community.
UNIDENTIFIED MAN #2: We have to make sure that our cities are safe.
UNIDENTIFIED WOMAN #2: If other cities can do it, we can do it.
GREENE: For thousands of years, city engineers have tried to corral water - think aqueducts.
DAVID SEDLAK: That's really the core of modern water infrastructure, and it's the ancient idea that the Romans gave us.
GREENE: That's David Sedlak. He's author of the book "Water 4.0."
SEDLAK: Collecting water somewhere on the outskirts of the city, sending it with gravity into the city, and then when we're done with it, we put it back underground in a sewer and send it on its way.
RENEE MONTAGNE, HOST:
That's the way most cities are designed. You could hear the echoes of that ancient plumbing all around Los Angeles last month.
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MONTAGNE: Rain, precious rain - answered prayer amid an epic drought, just pouring off a roof, through a downspout and straight into the sewer.
GREENE: Now some urban designers want to change this. They say in this age of climate uncertainty and drought, a downpour should be captured - used for drinking water or for irrigation. But most of the time, it's banished to a river and on out to the ocean, which is where we find Amy Standen from member station KQED.
AMY STANDEN, BYLINE: If you were to follow a drop of rain from the sky and onto an LA sidewalk, eventually you'd end up here, at the mouth of the Los Angeles River. I'm putting air quotes around the word river here because in the 1940s, engineers turned the LA River into a narrow, concrete channel. Today, it's more like a 51-mile-long bathtub that empties out here, at the port of Long Beach.
STANDEN: Does any part of this to you look like a river?
STEVE APPLETON: Um...
STANDEN: Kind of, says my kayak guide Steve Appleton. Look at all these shorebirds dive-bombing for supper around us.
APPLETON: Those were pelicans - all those kerplunks.
STANDEN: But he says this is a river in name only. Really, it's a flood control channel, which is why we turn our kayaks around at a sign that specifically prohibits against anything that might be construed as recreational.
APPLETON: (Reading sign) Warning, danger, no swimming, diving, waterskiing, jet skiing, sail boarding or other water contact sports prohibited - LA County flood control channel north of Ocean Boulevard bridge.
STANDEN: In a rainstorm, all that runoff from the sewers could surge through the channel and right at us. Of course, this river was once dangerous to more than just kayakers. Before it was channelized, the LA River could flood disastrously. Entire towns were wiped out. In 1938, a flood killed more than a hundred people. With the river caged by concrete...
APPLETON: It stabilized this constant threat.
STANDEN: The city could develop right up to the river's edge, paving over the floodplain in the process. The problem today is the city needs that rain. It can't afford to just send it out into the ocean anymore. Almost 80 percent of California is an extreme drought. That's a technical term, by the way - just one not shy of exceptional drought. And so there's a call now to build cities like sponges, which brings us to Elmer Avenue, a working-class neighborhood, where Rick Martin is out on his morning constitutional.
RICK MARTIN: On a, you know, walking regimen here. I can't really stop.
STANDEN: Oh, can I walk with you for a minute?
MARTIN: Sure, sure. Go ahead.
STANDEN: Martin walks on Elmer Avenue because this is the most beautiful block in the neighborhood, thanks to a $3 million makeover with permeable driveways and snazzy, drought-tolerant landscaping.
MARTIN: I'd like all the blocks to look like this. But I can't imagine they would spend this kind of money for the whole city.
STANDEN: Hadley Arnold would love it if they did. She's my guide today and cofounder of the Arid Lands Institute, a nonprofit in Burbank dedicated to the decidedly non-ancient Roman idea that cities should, wherever possible, soak up every raindrop.
HADLEY ARNOLD: Most of our neighborhoods in Los Angeles - we are required to send some storm water off of our properties as fast as possible - get it into a storm drain, get it out to sea.
STANDEN: Treating it like waste?
ARNOLD: Treat it like waste. Exactly.
STANDEN: Elmer Avenue is an experimental block that soaks it up...
ARNOLD: To treat it as a precious resource.
STANDEN: Here's how it works. Along each sidewalk is what's called a bioswale, a sort of gully filled with drought-resistant plants. When it rains, the water collects and filters down into cisterns buried below the street.
ARNOLD: In an average rain-year, this block puts enough water for approximately 30 families for a year into the ground.
STANDEN: That's amazing.
ARNOLD: Yes it is.
STANDEN: Arnold's organization would like to scale this up. They've mapped the region to help developers find the best spots for water to percolate down. To Arnold, this is part of a grand urban design challenge. She points up at the peaked roofs that most houses on Elmer Avenue have. Look at those, she says. They're designed for snow and ice, not the desert. Roofs here should look different.
ARNOLD: Roofs that are like a wide mouth open to the sky, roofs that are like a cup or a bowl or an umbrella turned upside down.
STANDEN: To catch as much rain as possible. And plumbing should be smarter, she says. We shouldn't be flushing our toilets with water that we could drink.
ARNOLD: In the future, we will be using water multiple times, and we will probably have multiple grade waters.
STANDEN: As we leave Elmer Avenue, we imagine an entire city designed like this - like a sponge. What would William Mulholland have thought of that? Mulholland is the engineer born in 1855 who masterminded California's water system. And he's memorialized, appropriately, with a big Roman-style fountain. Hadley Arnold and I are the only ones here. Cars zip by. And today, the fountain happens to be turned off. It makes us wonder what the monuments of a much drier future might look like.
ARNOLD: The ace in our species' pocket is the ability to innovate. And I think the single biggest question in front of us right now is the rate at which we do it. Can we do it fast enough, given the urgency?
STANDEN: Standing in about eight inches of rather gunky water at the William Mulholland memorial fountain, this is Amy Standen for the NPR Cities Project.
GREENE: And you can follow the NPR Cities Project on Twitter @NPRcities. You can follow us @MorningEdition.