Even without rainfall, the gutters, channels and storm drains of Los Angeles County pulse with about 330 million gallons of water every day.

Enough water to supply 668,000 typical Southern California homes in a year — unaccounted water streaming over green lawns, down paved streets and concrete channels. Water wasted to the ocean during one of the worst droughts in California history.

Most of this dry-weather runoff originates with homeowners who overwater lawns. Next, it comes from over-irrigated golf courses, parks and ball fields, leaky water mains and fire hydrants as well as industrial outflows from factories.

Water managers from the South Bay to the Antelope Valley know about dry-weather runoff but have let it pass them by because it was seen as miniscule when compared to billions of gallons of potable water imported from Northern California and the Colorado River.

Now that those sources are drying up due to decreases in snowpack in the Sierra Nevada and environmental uses of water to keep fish and wildlife alive in the San Joaquin-Sacramento River Delta, engineers and legislators have turned their eyes to this overlooked source as a supplement to outdoor water supplies.

“Dry-weather runoff has been the poor, forgotten Cinderella out there,” began Esther Feldman, president of Community Conservation Solutions, a nonprofit based in Venice that has studied the unusual source of water for eight years and helped contribute to a sea change in state water policy.

On Sept. 25, Cinderella was discovered. Gov. Jerry Brown signed SB 985 by state Sen. Fran Pavley, D-Agoura Hills, which will require water agencies to consider dry-weather water capture in future water-saving plans and water-recycling projects.

Read more in Steve Scauzillo’s story RUNOFF.