As a hedge against water shortages and population growth, Orange County, Calif., has begun operating the world’s largest, most modern reclamation plant — a facility that can turn 70 million gallons of treated sewage into drinking water every day.

The new purification system at the Orange County Water District headquarters cost about $490 million and comprises a labyrinth of pipes, filters, holding tanks, and pumps across 20 acres.

Almost four years after construction began, the facility is now purifying effluent from a neighboring sewage treatment plant run by the Orange County Sanitation District, a partner in the venture.

The finished product will be injected into the county’s vast groundwater basin to combat saltwater intrusion and supplement drinking water supplies for 2.3 million people in coastal, central, and northern Orange County.

But before that can be done, state health officials must certify that the reclaimed water meets drinking water standards. Officials expect the approval to be granted before opening ceremonies January 25.

“Our sources from [the Sacramento-San Joaquin Delta] and the Colorado River are becoming unavailable,” the general manager of the water district, Michael Markus, said. “This will help drought-proof the region and give us a locally controlled source of water.”

Last month, for example, a federal judge ordered a 30% reduction in fresh water pumped from the Sacramento-San Joaquin Delta to protect the tiny delta smelt, a threatened species. The region, which is facing myriad environmental problems, is the hub of California’s water system.

If the reclamation plant’s full potential is realized, officials say, up to 130 million gallons a day could be added to the county’s fresh water supply, lessening the region’s dependence on outside sources.

Basically, the facility takes treated sewage, which would have been discharged into the sea, and runs it through an advanced filtration system.

Officials say the final product is as clean as distilled water and so pure that lime has to be added to it to keep it from leaching minerals out of concrete pipes, thus weakening them.

The effluent is first pumped into the reclamation plant from the sanitation district’s sewage treatment facility next door. The brackish water, which smells of deodorizer, flows into 26 holding basins equipped with 270 million microfilters — thin straws of porous material with holes no bigger than three-hundredths the thickness of a human hair.

From there, the water is forced under high pressure through a series of thin plastic membranes housed in rows of white cylinders. Next, it is dosed with hydrogen peroxide and bombarded with ultraviolet light to neutralize any remaining contaminants.

At this point, the water is free of bacteria, viruses, carcinogens, hormones, chemicals, toxic heavy metals, fertilizers, pesticides, and dissolved pharmaceuticals.

Though it is good enough to drink, the scrubbing isn’t finished. Once the state approves, up to 70 million gallons of treated water a day will be pumped into the county’s giant underground aquifer. It will be cleansed further as it percolates through the earth to depths of up to 1,000 feet.

“This is as advanced a reclamation system as you are going to get right now,” said Krista Clark, director of regulatory affairs for the Association of California Water Agencies, a nonprofit organization that represents 450 government authorities.

At $550 an acre-foot, the recycled water is slightly more expensive than supplies brought in from Northern California. But water district officials predict that the cost of the treated water will become more competitive as the price of imported water rises.

The reclamation plant also will dramatically reduce the volume of treated sewage discharged daily off the Orange County coast. The sanitation district now releases about 240 million gallons a day through its ocean outfall — an amount that could be cut by more than half given the potential of water recycling.

Sanitation and water district officials hope the new plant will become a model for governments trying to cope with water shortages, drought and the increasing demands of growing populations.

Projects similar to Orange County’s are under study in Texas, Florida, Australia, Singapore, and elsewhere in California.