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.)