Every drop of rain in the Bay Area eventually flows to San Francisco Bay. Throughout history, that hasn’t been a problem. Most rain soaked into the ground and made its way gradually into creeks that emptied into the Bay.
But with so many roads, driveways, sidewalks and roofs in our urban area, rain rushes across hard surfaces, picking up trash, oil, pesticides and other pollutants. In most Bay Area communities, the contaminated rainwater zooms down a storm drain into a concrete culvert that dumps it—unfiltered and untreated—into creeks or the Bay itself.
Storm water pollution is one of the largest sources of contamination in the Bay. Moreover, it is difficult to control, because it comes from many places and picks up many different pollutants.
That’s why we built a permeable backyard patio at our house. Our patio soaks up rain that falls on our roof and flows across our small lot, keeping the rainwater from running off into the street. Our roof drainpipe connects underground to a large hole beneath the patio. The hole contains coarse gravel with plenty of air space to hold rainwater, which filters slowly into the surrounding soil. The patio’s fine granite gravel surface also absorbs rain.
A rain-absorbing patio is one way to keep rainwater from leaving your property and picking up pollution on its way to the Bay. Here are more:
Rain gardens work similarly to my patio. Areas landscaped with wildflowers and other native vegetation soak up rain that flows off a roof, driveway or other impermeable surface. In a storm, the rain garden fills with a few inches of water that slowly filters into the ground. Rain gardens absorb 30 percent more water than the same area of lawn.
Sidewalks and driveways can be paved with surfaces that keep rain from running off into the gutter. A special kind of concrete called pervious concrete allows rain to pass through into the soil below. Another option is interlocking concrete pavers separated by joints filled with small stones.
Rain barrels are easy, low-cost ways to collect and use rain water to irrigate a garden. Rain runs from roof gutters to a pipe that empties into a barrel. A screen keeps leaves, debris, and mosquitoes out of the barrel. A hose is attached near the bottom for irrigation. Indeed, roofs are an amazing source of water. In an average rainfall year, a 1,000 square-foot roof in San Rafael can collect up to 20,000 gallons of rain. Rain barrels typically hold 50 to 100 gallons; you can install more than one. Larger storage tanks, called cisterns, can be installed above or below ground.
Graywater systems are a way to go beyond capturing rainwater and irrigate a garden with used water from washing machines, showers and sinks (but not toilets). Graywater systems vary, but most have a valve that can be switched to direct the graywater into a garden or back to the sewage system. Using biodegradable soaps—without bleach, boron, dye or salts—keeps graywater safe and fertilizes plants. Graywater can be used to water fruit trees and other edible plants, as long as it doesn’t come into contact with the edible parts.
Harvesting graywater keeps relatively clean water out of sewage treatment plants, so less treated water is released into the Bay. A home with a graywater system also needs less piped water. "Using graywater is a small and powerful change we can make that can have a big effect. One household can save tens of thousands of gallons of water a year," said Laura Allen, co-founder of the Bay Area nonprofit Greywater Action.
Capturing water from one roof or re-using water from one washing machine are small steps—but with seven million people living in the Bay Area, small steps add up. Bay-friendly home and garden projects are easy, low-cost ways to help conserve water, prevent flooding, and reduce pollution in San Francisco Bay.
Greywater Action, www.greywateraction.org
Information on systems for using water from washing machines, showers, and sinks to irrigate plants. Classes for do-it-yourselfers and listings of professional installers.
Berkeley EcoHouse, www.ecologycenter.org/ecohouse
A demonstration home and garden with a graywater system, rainwater cistern, plus many more ecological features. Classes and tours.
Urban Farmer Store, www.urbanfarmerstore.com
Rainwater harvesting equipment and training workshops at stores in San Francisco, Richmond, and Mill Valley. Richmond store has discounted rain barrels for Oakland residents.
Sonoma County Master Gardeners, www.ucanr.org/sites/scmg
Information on building rain gardens.
Interlocking Concrete Pavement Institute, www.icpi.org
Information on local contractors who install paving that absorbs rain.