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Why we can — and cannot — collect rainwater in places like California

MARY LOUISE KELLY, HOST:

A bomb cyclone hit California this week, knocking out power, downing trees, dumping massive amounts of water. Now, that last one, massive amounts of water - it's interesting because all that rain is hitting in a state that has been stricken with drought. Some California residents are watching this precious resource wash away and wondering, why can't we save the water for later, for times when we desperately need it? Well, Andrew Fisher, hydrogeologist and professor at UC Santa Cruz, attempted to answer that question in an op-ed for The LA Times. And we have brought him here to try to answer it for us. Professor Fisher, welcome.

ANDREW FISHER: Thank you. It's good to be here.

KELLY: What is the short answer? How much, if any, of all this rain that has fallen on California this week - how much can be captured for later?

FISHER: Some of it can be captured for later. But the short answer is it falls so quickly that we lack the ability to take that water and set it aside quickly enough in a place where we can store it for later.

KELLY: So it's a storage issue. That's a major challenge - is you have storage tanks, but they're full. And so there's nowhere for it to go.

FISHER: Right. The primary forms of storage for water in California are the snowpack that typically accumulates annually and then reservoirs behind dams and then groundwater aquifers. And the challenge is that when we get a lot of rainfall like this, it's not forming snowpack in lower areas.

KELLY: Sure.

FISHER: It might form some snow at higher elevations. And reservoirs tend to fill up rather quickly, and then we have aquifers. And they have space, but it's hard to get water where it needs to be so it can infiltrate into the ground. And even then, it's hard to get it in fast enough.

KELLY: It sounds like you're describing a number of challenges. There's the storage challenge. There's the, OK, if you have managed to capture and save the water, how do you get it to where you are going to need it at some point down the road? That's a whole different challenge. And then are there also issues with ability to treat the water, that not all the water that gets captured is suitable to push back into people's pipes?

FISHER: Absolutely. These are all challenges, and there are additional challenges. Because the water falls at a very fast rate and it creates a hazard, we do tend to treat storm water as a nuisance and try to get it off the landscape as quickly as possible. So when we have the option to hold that water back a little bit and let it percolate into the ground, this is a tremendous opportunity. However, as you note, sometimes that water is not suitable for drinking. That's an additional bottleneck because you can't treat the water as quickly as it's falling or as quickly as it's running off. And, of course, the level of treatment you need might vary from place to place, and it does create quite a logistical challenge in order to deal with that water.

KELLY: In the meantime, all the extra water that's fallen this week is going where - just running eventually toward the sea?

FISHER: Yeah. It's going to a variety of places. A lot of it will end up rolling out to the ocean. Some of it is being diverted, and we're collecting some of this storm water and directing it towards infiltration basins, where it can percolate into the ground. There are other folks around the state and around the western United States who run similar projects. So people are trying to collect as much of this storm water as we can when we have this opportunity. It turns out a lot of water is falling. A lot of water is running off. So a large part of that does end up flowing out to the ocean.

KELLY: I hear y'all have more rain on the way this weekend.

FISHER: Yeah. That's what we hear. I've got a student group that's out right now sampling from some of our systems, and we dashed out here between the storms because it's an opportunity when it's safe to go collect water samples and see how water quality looks. I'll just note that we have to get more water in the ground. We simply have no choice.

KELLY: UC Santa Cruz Professor Andrew Fisher, thank you.

FISHER: You're welcome. Thank you.

(SOUNDBITE OF JAN HAMMER GROUP SONG, "DON'T YOU KNOW") Transcript provided by NPR, Copyright NPR.

Mary Louise Kelly is a co-host of All Things Considered, NPR's award-winning afternoon newsmagazine.
Erika Ryan
Erika Ryan is a producer for All Things Considered. She joined NPR after spending 4 years at CNN, where she worked for various shows and CNN.com in Atlanta and Washington, D.C. Ryan began her career in journalism as a print reporter covering arts and culture. She's a graduate of the University of South Carolina, and currently lives in Washington, D.C., with her dog, Millie.