A water disinfection facility now under construction 30 miles north of Manhattan will use ultraviolet (UV) light to destroy waterborne pathogens in the reservoir pipes there that serve the Big Apple. New York City currently applies chlorine to kill waterborne organisms such as E. coli, Giardia and Cryptosporidium. But the U.S. Environmental Protection Agency has for a decade urged communities to cut back on the chemical as much as possible.

The UV facility, scheduled to turn on in 2012, is expected to be the world’s biggest. It will consist of 56 units that can each cleanse 40 million gallons a day. Individual units will contain 144 large, high-output UV lamps, which are similar to fluorescent lightbulbs but without the phosphor coating that protects people from prolonged exposure to UV rays. The light “alters the DNA of the bacteria in the water, making them unable to reproduce,” says Jason Cerny, lead mechanical designer at Trojan Technologies, the system’s manufacturer.

San Francisco’s Tesla Portal drinking-water facility is also installing a set of 48 UV reactors made by Calgon Carbon to treat up to 320 million gallons of water daily.