It seems out of place and unstuck in time. What is a classical Greco-Roman style temple complete with ornate Corinthian columns, manicured lawns and a cypress-lined reflecting pool doing on a country road at the northern end of Silicon Valley?

An over-the-top gazebo for some start-up billionaire's sprawling estate perhaps?

The Beaux Arts monument actually marks an event of momentous importance for San Francisco — the arrival of the first Hetch Hetchy water to San Francisco. It took 20 years to complete the damming of Yosemite’s Hetch Hetchy Valley and construction of a 167-mile, gravity-operated aqueduct in the early 20th century.

On Oct. 28, 1934, some 20,000 San Franciscans gathered by the southeast corner of the Upper Crystal Springs Reservoir to watch the snow-fed Sierra Nevada water spill from the aqueduct and into the lake. It was a big deal, attended by numerous dignitaries including a U.S. senator and the Secretary of the Interior Harold Ickes, and broadcast on national radio. Like the gushing water, purple prose cascaded in the Chronicle's coverage:

"This was mere water, but to those who watched it, it might have been wine. It was the wine of a great dream fulfilled, of a great and often heartbreaking task accomplished, the wine of triumph in a strife with Nature ..." wrote reporter Royce Brier.

Today San Franciscans take their tap water for granted despite its triumph over nature. Even though Hetch Hetchy water is arguably the purest in the nation, bottled water of less quality sells briskly here. People pay good money to drink inferior water.

A temporary water temple, mostly constructed of plywood, was erected for the 1934 event. The temple that rises above the site now, the Pulgas Water Temple, was built four years later. It resembles the 1910 Sunol Water Temple, which marks the confluence of three subterranean water courses in the East Bay.

In the early 1900s, one couldn't have too many water temples.

The San Francisco Water Department's Assistant General Manager for Water Steve Ritchie notes that a pipeline didn't offer much in the way of visual interest, but a temple could get people's attention.

"It doesn't really serve any purpose. It's just a physical feature above ground so you can see something," says Ritchie. "A symbol."

The Pulgas Water Temple was designed by William Merchant with stone work by master carver Albert Bernasconi. If it seems reminiscent of San Francisco's Palace of Fine Arts, it's no accident. Merchant was trained by the palace's architect, Bernard Maybeck.

The architecture may be Ancient Greek, but the message is Old Testament. A massive stone ring that rests on the temple's columns some 60 feet above the ground contains the words, "I give waters in the wilderness and rivers in the desert, to give drink to my people." (Isaiah: 43:20.)

For many years, you could not only get a refreshing water fountain drink at the temple, you could sneak a swim as well.

Hetch Hetchy water used to flow straight through the monument over a small "C"-shaped waterfall in a vault below the temple's floor and then continue down a canal about 800 feet before emptying into the reservoir.

In the old days, teenagers would slip onto the grounds after hours and jump 10 feet or so into the rushing water, ride through the canal and then plunge into the reservoir.

Ritchie called it an attractive nuisance.

At some point, authorities decided that an adolescent-flavored water supply was not in the public's interest. An industrial-strength mesh was installed over the opening in the well. That ended the Pulgas temple water slide ride for good.

Almost no water travels through the monument now. Hetch Hetchy water must be treated with chlorine and ammonia in Sunol before it can be sent to Bay Area faucets, but the water designated for Crystal Springs Reservoir is now diverted to a second treatment plant on the Peninsula. There it is stripped of the additives before entering the reservoir. If the water were left untreated, the chemicals could harm Crystal Springs' fragile ecosystem.

Asked about the perennial calls by environmentalists and conservationists to empty Hetch Hetchy and restore the "other" Yosemite valley, Ritchie says it would be a grievous mistake to drain the reservoir. Not only is having a reliable water source critical for San Francisco amid a changing climate, he says, but the system also supplies emissions-free hydropower to municipalities, such as the electricity to run Muni buses.

The benefit is worth the cost, he maintains.

"You still have a beautiful granite valley above the 300 feet of water," Ritchie says.

More about the Pulgas Water Temple and Hetch Hetchy water:

—Where the "Pulgas" comes from: Because the temple sits on the former Rancho de las Pulgas, an early Spanish land grant, it was named "Pulgas," possibly by people who weren't aware the word means "fleas" in Spanish and Portuguese.

San Francisco Chronicle Archives

—"Oh Girls!": Nelson A. Eckart, general manager of the San Francisco water system in 1934, touted Hetch Hetchy water as a miracle hair treatment. He claimed the water would beautify and add sparkle to the hair of San Francisco women. In addition, housewives would benefit because the soft water would cut soap bills and whiten the family linen. The Chronicle's Oct. 29, 1934 headline read: "Oh Girls! Get Set For Hetch Hetchy Hair!"

—Some 20,000 people visit the water temple each year.

—About 20 weddings are held on the grounds of the temple each year. Weddings and other events must be booked in advance.

—No impromptu parties are allowed, not even toga parties. No picnics or barbecues. No dogs either, which probably is just as well given the fleas.

—The temple is open five days a week, from 9 a.m. to 3:30 p.m. Admittance is free. On weekends, the landmark is not officially open, but walk-ins and bicyclists can visit the landmark. Note: A 3.8-mile segment of Cañada Road, including the the turn-off for the water temple, is closed Sundays between the Filoli entrance and Highway 92 to allow for non-motorized activities including jogging, bicycling, hiking, roller-skating and walking.

—Limited parking is available on weekdays, 30-minute maximum.

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Mike Moffitt is an SFGATE Digital Reporter. Email: moffitt@sfgate.com. Twitter: @Mike_at_SFGate