As America's expanding urban areas struggle with major water supply shortages and runoff pollution problems, capturing rainwater from rooftops provides a tremendous untapped opportunity to increase water supply and improve water quality, according to a recent analysis on "Capturing Rainwater from Rooftops" by the Natural Resources Defense Council (NRDC).

In its report, NRDC demonstrates the benefits and potential of rooftop rainwater capture, a "green infrastructure" practice that can be used to retain stormwater runoff on-site, by analyzing ways in which eight diverse U.S. cities could incorporate this simple water collection approach. By comparing annual rainfall totals to rooftop coverage, NRDC determined that opportunities exist in each city to capture hundreds of millions of gallons of rainfall every year for reuse. By doing so, residents of these communities would obtain inexpensive onsite water supplies for non-potable uses, such as yard watering and toilet flushing; reduce runoff pollution; and would lower energy costs associated with treating and delivering drinkable-quality water.

"Our analysis shows that solutions to one of America's biggest urban challenges are right in front of us – in this case, literally falling from the sky," said Noah Garrison, lead author of the report and NRDC water policy analyst. "The potential exists for cities throughout the U.S. to capture hundreds of millions or even billions of gallons of rainwater each year from urban rooftops. We encourage policymakers to look closely at the bottom-line benefits of rooftop rainwater harvesting, and consider implementing policies and incentives that generate more momentum for rainwater collection while making the practice more accessible as well."

Specifically, NRDC's report illustrates opportunities for capturing, treating and supplying harvested rainwater for non-potable purposes in Atlanta, Ga.; Austin, Texas; Chicago, Ill.; Denver, Colo.; Fort Myers, Fla.; Kansas City, Mo.; Madison, Wisc.; and Washington, D.C. Several success stories also demonstrate the effectiveness of rooftop rainwater capture for new construction in New York, N.Y., and redeveloped buildings in Santa Monica, Calif. The total annual volume of rainwater falling on rooftops in these cities alone, if captured in its entirety, would be enough to meet the water supply needs of at least 21 percent to as much as 75 percent of each city's population.

The report comes as 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 encourages the agency to adopt national standards for on-site stormwater retention that will increase green infrastructure approaches such as rainwater harvesting. As a result, communities can effectively transform polluted runoff flowing to our waterways into captured rooftop rainwater used as an on-site water supply resource.

"Urban areas struggling with water supply issues and runoff pollution should look to this report for ideas and encouragement," said Jon Devine, senior attorney in NRDC's water program.

NRDC encourages cities and states to develop policy options and incentives to encourage more rainwater harvesting. These include:

• Adopt storm water pollution control standards that require on-site volume retention.
• Adopt standards that require or promote rainwater harvesting and/or water efficiency.
• Review building, health and plumbing codes for barriers to reusing rainwater.
• Provide incentives for decreasing storm water runoff and promoting water conservation.
• Require use of rainwater harvesting on all public properties.

The complete NRDC report is available HERE.

For more information on rooftop rainwater capture, please see Noah Garrison's blog.

Photo: Steve Crane