In a drought-plagued state begging for rain, most of what falls on urban areas of California is allowed to run off into the ocean.
Systems to capture and recycle a significant amount of rain run-off are years away, according to watershed experts, though they see progress in reducing the amount of pollution that run-off carries out to sea.
However, runoff this week was expected to deliver enough contaminants into Santa Monica Bay that public health officials issued a warning for beach-goers to avoid areas near storm channel outlets.
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The warning will remain in effect at least through Thursday evening, and then be re-evaluated, according to a statement issued by Jeffrey Gunzenhauser, MD, interim health officer for Los Angeles County.
Pollutants carried into the bay by the flood control system typically include trash, oil from roadways, and excrement from dogs whose owners failed to pick up after them.
"Our wet weather is when the largest amount of pollution gets flushed out to the bay," said Sarah Sikich, VP of the environmental organization Heal the Bay.
But surveying the beach in Santa Monica at the foot of Pico Blvd. during Tuesday's rain, as a torrent of runoff rushed out of the Pico Kenter storm drain, she saw fewer plastic bags, styrofoam cups and disposable food containers than seen in years past before many communities imposed restrictions.
Another factor is steps taken by beach communities to intercept the trash that still does get into storm drains.
Since the millennium, Santa Monica has installed several underground filtration systems in the main storm channels that empty into the bay.
"We're screening and separating out the solids so they don't go to the ocean," said Neal Shapiro, Watershed Programs Coordinator for the City of Santa Monica.
Lifting a maintenance cover in a parking lot near the pier revealed trash swirling inside the chamber filtering runoff from the city's downtown area. It's called CDS--Continuous Deflective Separation-- and it has no moving parts, instead relying on the energy of the rushing runoff .
In the next two years, the filtration system for Pico-Kenter, the highest volume drain in Santa Monica, will be upgraded to trap more of the solid contaminants, Shapiro said.
The Bay City has also invested in a treatment plant dubbed "SMURFF"--Santa Monica Urban Runoff Recycling Facility." It captures, treats and recycles so called "dry" runoff that comes from yard watering and other water uses when it is not raining.
The recycled water is then put to use on municipal properties for irrigation and other non-drinking purposes.
Some of the larger sanitation and water districts also recycle sewage, often using the treated water to replenish groundwater reserves.
SMURFF can process as much as 500-thousand gallons a day, Shapiro said, but lacks the massive storage capacity to accommodate the vastly larger surges of runoff that occur during times of rain.
In Los Angeles county during a typical rain, as much as 10 billion gallons of rain runoff goes out to see, according to an estimate cited by Heal the Bay.
"I see the water running off and it's like, 'Boy, if we could capture that or let it get back into the ground,'" Shapiro mused.
Large-scale systems appear less feasible for now than runoff recovery on a neighborhood scale, where water can be captured with rain barrels and re-designed landscaping.
Meantime, after three years of drought, Californians could only watch most of the recent rain disappear out to sea, still carrying some trash with it.
"This is a great opportunity to raise awareness," said Sikich "Not only of the waste going into the Bay, but of the water that is so precious."