By now you’ve heard about the epic drought threatening every California water user, from almond growers to swimming pool owners, resulting in mandatory cutbacks and ostracism from neighbors for being the last on the block with a green lawn. So would it surprise you to learn that the state actually has more than enough water to go around?

About a decade ago, the blue-collar community of Sun Valley in Los Angeles County was faced with flooding that impacted homes and businesses during winter rains. The county had planned a $47 million storm sewer system to drain the floodwaters from streets and dump it in the Pacific Ocean via the Los Angeles River (itself now a mostly concrete flood management canal). Instead, clever community planners decided to invest those funds in underground cisterns that would capture the water for later use.

A dilapidated city park was remodeled with cisterns below, as were medians along broad boulevards that were themselves underwater during heavy rains. The result was a system, using ancient Roman technology, that captures 8,000 acre feet of water each year. That’s about twice what the entire city consumes, solving the flooding problem and creating a source of fresh water for thousands of residents. By the way, the investment also gave the city a new park with ball fields and picnic grounds and higher adjacent property values.

But could something this simple be the solution for a thirsty state that is getting hotter, growing faster, and producing more food crops than ever before? According to the National Weather Service, the average annual rainfall in Los Angeles for the past 100 years is about 14 inches, more than enough to serve the needs of the region and then some.

During the decade from 2003 to 2012 we had wet years of nearly 38 inches of rain and dry ones of less than 4 inches, but the average was still just under 14 inches, meaning there is no drought in the most populous region of the state.

So what’s the problem? For the past 150 years, the goal was to address the same challenge that Sun Valley faced: not a lack of water, but too much water during the brief, intense rainy season. So Southern California built storm sewers and concreted the rivers to efficiently carry all that fresh water into the ocean.

The answer to the drought, therefore, is to stop wasting this valuable resource. If we captured and used the water that already falls here, we could turn off the tap from the north and leave that water for farmers. Just as we discovered in California that sunlight falling on every rooftop can be harnessed to generate energy, right at the place it is used, we can capture the water that falls on those same landscapes for use where it’s needed. In fact, the Los Angeles non-profit TreePeople has been demonstrating for years that every type of building or land use can do what Sun Valley has done, or what solar panels do for energy generation–decentralize.