A Tour of New York City's Croton Water Filtration Plant

This photo gallery spotlights New York City's first and only water filtration plant, which will sit below a golf course in the Bronx.

New York City's water is so fresh and clean that it remains one of only five large cities in the nation that isn't required to filter its drinking water. That will change slightly in 2012, however, when the Croton Water Filtration Plant goes online and starts filtering about 10 percent of the city's drinking water.

Back in 1993, the U.S. Environmental Protection Agency ruled that the Croton Watershed -- one of three operated by the city -- required filtering, launching an initiative that has become one of the largest, most expensive water filtration projects in the country. Located on a golf course in the Bronx, the plant was required to fit on a footprint smaller than 10 acres, forcing engineers to blast down more than 90 feet into bedrock, and then stack the various filtration components on top of each other.

Today, the estimated $2.8 billion project is a construction beehive, with workers installing massive pumps and pipes, huge holding pens, enormous tanks and miles of electrical wiring. On a cold, winter day complete with falling snow, men and women in hardhats work steadily underground in the massive 600-foot-long caverns of concrete, their radios blasting Jimi Hendrix or Lady Gaga as they bolt and weld the filtration plant to life.

At the very bottom of the site is the 9-foot-diameter, 8,000-foot-long tunnel that will connect the plant with the aqueduct that delivers water from reservoirs more than 60 miles away. Bernard Daly, the site's executive construction manager, stands in the middle of the tunnel and tries to explain the immensity of the project he oversees. Talking in a clipped Irish accent, Daly explains that the tunnel is about to be sealed off, the first of the final stages of construction that will end in another 24 months or so, if all goes according to plan. "Above, we're going to build a golf driving range over the entire site. You won't know you’re standing on a filtration plant," he says, knowing that the public will never see what he and his workers have created.

Tina Trenkner is the Deputy Editor for GOVERNING.com. She edits the Technology and Health newsletters.