"As we've covered our urban areas with hardscape, roads, and driveways and rooftops, that water has no place to soak in, so basically it just sheets off as soon as the rain starts," Dan Carney from the Marin Municipal Water District said.
When water flows over roofs and roads, it picks up oil, chemicals, dirt and bacteria -- pollutants that end up in our creeks and waterways. Stormwater, once pure as the falling rain, is now a huge environmental problem.
"The EPA estimates that every three weeks in the U.S. we have the equivalent of the Exxon Valdez oil spill, just from oil coming off of parking lots, roads and oil that's improperly disposed of along roadsides," Paola Bouley from the Salmon Protection and Watershed Network.
And it's not just pollution. Fast-running stormwater also creates serious erosion. A Mill Valley backyard has a huge crevice, five feet deep, created by neighbors diverting their runoff on to other people's property.
"It also erodes the banks where the trees are and undercuts the roots of the trees and generally disturbs the whole eco-system," Carney said.
Fast running stormwater is often disastrous for wildlife, including salmon.
"In Marin County, we have so much stormwater runoff that runs off our landscapes into our creeks, that in the winter, it's pretty much blowing baby fish out of the stream system and out to sea before they are ready to go," Bouley said.
Salmon also need clean gravel to lay their eggs. But a lot of their habitat is murky with sediment stirred up by too much runoff.
The EPA is now writing new regulations on how to handle storm water runoff. They probably won't be ready for two years, but in the Bay Area, several local agencies are already taking action.
"Trying to make sure that it's back to the natural way of doing business where when it rains, we actually use that water in a beneficial way," Ed Harrington from the San Francisco Public Utilities Commission said.
One success story is at San Francisco's Lake Merced. Stormwater used to run from the parking lot into the lake, but the lot was rebuilt so now rain water drains into gardens filled with native plants.
A project in San Francisco's Visitation Valley will have gardens to collect rain and instead of cement and asphalt. Part of the street is being covered with paving stones.
"They are pervious which basically means the water flows through the paver and through the gaps around the pavers," Kris Opbroek said.
So water soaks into the ground instead of ending up in a storm drain.
There are also a lot of things individuals can do, like designing your yard so water from your roof is routed into your garden, not on to the street or you can pipe your roof runoff into big barrels and save it to water plants.
In Marin, there are even free workshops and consultations to help you figure it out.
"For every 1,000 square feet of roof surface and one inch of rain, you catch 600 gallons of water," Bouley said.
Storm runoff comes from so many sources. It really is a problem where every little bit makes a difference.
San Francisco is so concerned about runoff, the city has just passed an ordinance for all new development over 5,000 square feet. Those new buildings will now be required to absorb most of their stormwater on site.
Written and produced by Jennifer Olney