How You Can Help Stop Rainy Season Pollution in the Bay

Feb 20, 2015
Deb Self
by Deb Self

Major storms that have arrived in the Bay Area during the drought carried a huge load of trash into San Francisco Bay. The trash is a visible sign of lots of additional pollution. When rain falls on roads, parking lots, roofs and other impermeable surfaces, it picks up pollutants that include trash, oil, pesticides, fertilizers and household chemicals. In most Bay Area communities, including those many miles from the Bay’s shore, the contaminated rainwater rushes down a storm drain that dumps it—pollutants, trash, and all—into the Bay or into creeks that flow to the Bay. 

This rainy-season contamination surge is one of San Francisco Bay’s most serious pollution problems, and when there’s a long time between storms, the pollution is even more concentrated. Before the Bay Area was built up and paved over, rain soaked into the ground and made its way gradually to creeks and the Bay, with the ground filtering out pollutants. Each of us can help restore some of this natural protection by keeping more rainwater in our yards and gardens, instead of allowing it to flow off into gutters where it can pick up and carry pollution. If we reuse the rainwater we’ve harvested, we’ll also conserve scarce water. And there are ways even those who don’t have a yard can help.

Here’s what you can do:

Reuse rainwater: Rain barrels are easy, low-cost ways to collect and use rainwater to irrigate a garden. Rain runs from roof gutters to a pipe that empties into a barrel, with a screen to keep out leaves, debris and mosquitoes. A hose is attached near the barrel bottom for irrigation. Rain barrels can be installed by both homeowners and tenants, as long as a tenant gets the landlord’s permission.

Roofs can supply large amounts of water. In an average rainfall year, a 1,000 square-foot roof in the Bay Area can collect more than 13,000 gallons. Rain barrels typically hold 50 to 100 gallons and you can install more than one. Larger storage tanks, called cisterns, can be installed above or below ground.

Plant a rain garden: Rain gardens are landscaped areas planted with wild flowers and other native vegetation. They soak up rain that flows off a roof, driveway, sidewalk or other impermeable surface. In a storm, the rain garden fills with a few inches of water that slowly filters into the soil beneath, where beneficial microorganisms break down pollutants. The water may recharge local groundwater supplies, or gradually make its way to a creek—minus the pollution it would carry if it flowed over paved surfaces into a storm drain.

Installing a sidewalk, driveway, or patio? Make it permeable: Permeable paving allows rain to sink through the pavement into the soil beneath, offering some of the same benefits as rain gardens. Options include a special kind of concrete called pervious concrete and interlocking concrete pavers separated by joints filled with small stones.

Encourage your city or county to help stop rainy-season pollution: Even if you don’t have a yard, you can encourage your local government to harvest and reuse the rain that falls on public property. Public buildings can be retrofitted or designed to reuse stored rainwater to irrigate landscaping, or for such uses as flushing toilets. Streets can be paved with permeable paving, like Berkeley’s new permeable paved block on Allston Way facing Berkeley High. Cities and counties can encourage residents to install rain barrels and require new privately developed buildings to be built to reuse rainwater. Local governments can also reduce trash pollution in the Bay by equipping storm drains with devices that capture trash.

Harvesting water from one roof or paving one driveway with porous concrete are small steps—but with seven million people living in the Bay Area, small steps add up. If we all do what we can, we can help reduce pollution in San Francisco Bay, while also making our region better able to withstand drought.   

The Internet has many sources of information on harvesting rainwater. These are good places to start:
• The California State Water Board’s Slow the Flow videos on YouTube have information on permeable paving, rain gardens and more. 
• The Urban Farmer Store, with three Bay Area locations,, carries rain harvesting equipment.
• For information on permeable paving, visit
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