WHITTIER >> Two water agencies signed an agreement Wednesday that will add 24 trillion gallons of recycled water a year to the ground water used by residents of 43 cities in southern Los Angeles County.

Four million residents from cities within the Water Replenishment District, from Montebello to Long Beach and Torrance to Cerritos, will have a local, reliable water source to boost well-head supplies. Soon, the WRD will no longer have to buy any water from the Colorado River or the Sacramento-San Joaquin River Delta in Northern California, a first for this district which manages two of the largest underground basins in Southern California, the Central and West Coast basins.

The addition of what amounts to 83,000 acre-feet of recycled water, as much water used by 160,000 families in Southern California, makes WRD the largest user of regulated recycled water in the nation, said Robb Whitaker, WRD general manager.

“We will be able to replace water imported from Northern California and the Colorado River. This represents an historic milestone,” said WRD board member Albert Robles, speaking at a ceremony at the San Jose Creek Water Reclamation Plant run by the Sanitation Districts of Los Angeles County.

With the two halfs of the state fighting over a plan to move water more efficiently from the Delta by building twin concrete canals and restoring habitat for salmon and the Delta smelt, weaning a large portion of Southern California off imported water sends a message of water independence.

Like America developing its own oil sources to replace foreign oil, California water agencies are tapping local water sources such as wastewater or salt water from the ocean that can make them water independent. By weaning themselves off imported water, agencies can plan for future water emergencies at lowered costs.

Rep. Grace Napolitano, D-El Monte, who serves on the House Committee on Natural Resources and the Subcommittee on Water and Power, called the agreement “drought protection” for the future when the effect of global warming intensifies. “Capturing more instead of letting it go to the ocean makes a lot of sense. We are ahead of the nation,” she said in her remarks.

The WRD and the Sanitation Districts have been working together developing, treating and injecting recycled water into the Central and West basins for 51 years. The efforts started in 1962, almost 20 years before the enactment of the Clean Water Act, said Grace Chan, general manager and chief engineer of the Sanitation Districts.

The Sanitation Districts treat sewage water from households and wastewater from industrial operations at 10 water reclamation plants. Water from its San Jose plant and Whittier Narrows Water Reclamation Plant is sold to the WRD for about $350 per acre foot, Whitaker said. If it were to buy imported water from the Metropolitan Water District of Southern California, that would cost $800 per acre foot, he said.

The water is treated by the sanitation districts in a three-step process, he explained. When WRD buys the water, it goes through a second three-step treatment process.

After that, the water is sent to the Montebello Forebay Spreading Grounds, where it percolates through hundreds of feet of sand and gravel until it reaches the water table. “In addition to the high level of treatment, another level of treatment is provided by nature in the ground. The soil treats the water. It polishes the water,” Whitaker explained.

State health department rules require the water to remain in the ground for six months. Whitaker said it can take a year or more to be pumped from the ground as potable water.

WRD as well as some 200 water purveyors it serves, test the water for chemicals, bacteria and other compounds. Also, recycled water is often blended with well water. “The process is highly regulated to assure compliance with the state regulations. We take that very seriously,” he said.

Water recycling in Orange County surged ahead of the WRD in recent years, he explained. But now the WRD will be the largest user of regulated recycled water.

Other agencies are further behind. For example, efforts to recycle water and pump it into the large San Gabriel Basin stretching north of Whittier Narrows to the foothills was stymied in the late 1980s by a small band of protesters who called it a “toilet-to-tap” program.