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David Beckman’s Blog

It's the Solution Hiding in Plain Sight

David Beckman

Posted February 15, 2012

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It’s the solution hiding in plain sight. Every year, billions of gallons of rainwater fall on our roofs. We let most of it drain onto sidewalks, streets, and parking lots. As it rushes over paved landscapes, it picks up chemicals and other pollutants and ends up being dumped into our rivers and lakes. Our beaches become dirtier and our communities lose a vital supply of water.

But if we harvested some of this rainwater instead of tossing it out, the benefits would be enormous.

A new report by NRDC, Capturing Rainwater from Rooftops, estimates that, even under conservative assumptions about water use, if Atlanta captured and used the first one-inch of rain that fell on just half of its buildings, it could supply enough water for about 48,000 people—nearly 10 percent of the city’s population. Meanwhile, Atlanta’s waterways would be cleaner and its nearby beaches would be safer for people to swim in.

We found similar benefits in other cities, including Denver, Austin, Fort Meyers, Kansas City, Chicago, Madison, and Washington, DC. Indeed, our analysis shows that capturing all of the rain falling on rooftops in these cities could meet the annual water supply needs of between 21 percent and 75 percent of each city’s population.

Cities across the country are discovering that like other green infrastructure strategies—pocket parks, grassy swales, rooftop gardens—rainwater harvesting can be a potent solution for dealing with two troubling water trends at once.

Demand for water is increasing in many places across the nation, as this nifty chart from U.S. EPA shows (the states colored in darker hues use water more intensely, and the projected population increases are shown as the numerals appearing over each state). 

But at the same time, pollution from a variety of sources—contaminated stormwater being one of the largest—reduces the amount of safe, clean water. Climate change further shrinks the amount of freshwater practically available in many parts of the country, by diminishing snowpack and altering rainfall patterns.

With America facing water scarcity in many places, the quality of existing water becomes a paramount priority. We can’t solve one issue without solving the other. Harvesting rainwater helps communities do both.

Rooftop harvesting reduces dirty stormwater and provides an inexpensive onsite supply for non-potable uses with little or no treatment or for potable uses with higher levels of treatment.

Right now, most people use drinking water for their daily residential needs, but up to 80 percent of domestic demand may not require drinkable water. For example, 270 billion gallons of water are used each week—a significant portion of it potable—to water 23 million acres of lawn in the United States. This watering bill costs $40 billion annually.

More than 11 percent of drinking water delivered to households and 25 percent of drinking water delivered to commercial buildings is flushed directly down the toilet, and along with it the money and energy used to treat and deliver the water.

Rooftop rainwater harvesting could easily be used for a big chunk of those non-potable needs, and generate enormous savings of drinking water in the process. Researchers at the University of Arizona concluded that if Tucson captured rainfall from roofs and used it for onsite landscaping, it could reduce residential water use by 30 to 40 percent.

Preserving our drinking water supplies, reducing our water bills, and keeping our beaches safe from contaminants. Rooftop rainwater harvesting delivers all these benefits. And like the other green infrastructure techniques I blog about, it also helps make our communities greener and inviting.

While many cities are already enjoying these benefits, it time we spread them around. Right now, the Environmental Protection Agency is in the process of updating its national standards for controlling runoff pollution from new development and existing paved areas.

NRDC’s report Capturing Rainwater from Rooftops offers new evidence for why the agency should adopt standards for on-site stormwater retention that will increase rainwater harvesting and other green infrastructure approaches. It will make it easier for city leaders, water managers, and developers across the country tap the water supply hiding in plain sight.

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Switchboard is the staff blog of the Natural Resources Defense Council, the nation’s most effective environmental group. For more about our work, including in-depth policy documents, action alerts and ways you can contribute, visit

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