Fountain Valley water treatment plant, an architectural marvel?

The Parthenon it is not.

There are no monumental facades, ornate columns or elaborate sculptures.

And set back from Ward Street in Fountain Valley behind a screen of trees and bushes, it’s barely even visible to passersby.

You’ve likely never seen it, but the Orange County Water District’s Groundwater Replenishment System is an architectural gem. Just ask the folks at Mammoth, an architecture blog that in January named the facility to its list of the best architecture of the decade.

The $480-million Groundwater Replenishment System, or GRS, is a complex of about a dozen buildings that takes wastewater — that’s a nice word for sewage — treated by the Orange County Sanitation District and turns it into pristine drinking water. The system, which opened in 2008, produces about 70 million gallons per day of water that are put into the groundwater table and ultimately end up in your bathtub and your drinking glass.

The GRS is so high-tech that it’s hard, at a glance, to comprehend what all those tubes, tanks, valves and ducts might be for. The Mammoth blog called it “a staggeringly futuristic feat of engineering and technology.”

With its sleek, post-industrial looks, the GRS has become a popular location for photo shoots. Sunglasses-maker Revo and Wired magazine have both photographed the space, and it has been considered as a location for a number of television and film shoots.

Gina DePinto, a spokeswoman for the water district, said she and her colleagues had never thought of the GRS as cutting-edge architecture but did know that it had turned heads in the engineering world. With a design spearheaded by the engineering firm of Camp Dresser & McKee, it has won several awards and is the largest water purification system of its kind in the world.

“It’s clean and it’s cool and it’s . . . high-tech looking,” DePinto said.

Planning for the Groundwater Replenishment System began in the mid-1990s, when Orange County’s rapid growth was straining the existing water systems.

The groundwater supply was being used faster than it could be replenished, and the dropping water table was allowing ocean saltwater to creep in and threaten the county’s main water source. (Groundwater makes up about 62% of the water consumed in northern Orange County; the rest is from the Colorado River and Sierra Nevada.)

At the time, most of the Sanitation District’s treated wastewater was pumped several miles out to sea and dumped. The new system sought to reuse much of that wastewater, which is clean enough to dump into the ocean safely but not to drink.

“We said, ‘Well, look, let’s put our resources together . . . and make some drinking water,’” DePinto said. “We’re going to need it.”

The Water District — which operates the GRS — receives more than 90 million gallons per day of treated wastewater from its neighbor at the Sanitation District and produces about 70 million gallons per day of purified water. The remainder is lost as waste and dumped in the ocean.

The first step in the GRS purification process is microfiltration, where treated wastewater is sucked through filters with holes that are about 300 times smaller than a human hair. The filtration removes bacteria, protozoa, viruses and sediment that might be left over after the sewage-treatment process.

Next is reverse osmosis, where the water runs through long, white plastic pipes and is forced by pressure through a series of membranes. Only the water can pass through the membrane pores, and contaminants are filtered out. After this step, the water is so pure that minerals have to be added back in to keep it from reacting with pipe materials.

The water is then exposed to ultraviolet light to kill any remaining bacteria. At this point, the water treatment process is complete and the water is drinkable.

The processed water is clean enough to be pumped directly into municipal water systems, but DePinto said “political concerns” have kept the Water District from doing so. The purification process has been labeled “toilet to tap” — a difficult proposition to sell to the public.

Instead, it is first added to the groundwater table and is later pumped out through wells.

About half of the purified water is pumped to Anaheim and into a series of basins, where it percolates into the groundwater and replenishes the water table.

The other half — some 35 million gallons a day — is put into 36 injection wells in Fountain Valley and Huntington Beach, which raises the groundwater table artificially to form a barrier against saltwater intrusion. This prevents the rest of the water supply from being contaminated.

Despite the elaborate process, DePinto said reusing wastewater through the GRS actually is the cheapest option available. Water produced through the system costs about $550 per acre-foot — equivalent to about 326,000 gallons — compared to $650 to purchase water from the Metropolitan Water District of Southern California and up to $2,000 to produce it through seawater desalination.

“Groundwater is the cheapest water out there,” DePinto said.

The GRS facility has room to expand in the future, which likely will be necessary as Orange County continues to grow.

“We’ve actually done a good job of conservation,” DePinto said. “Water demand hasn’t gone up [as much as] population. But I think until it hits someone in the pocket,” demand will continue to grow.