The World's Largest Ultraviolet System Is Now Purifying New York City's Water

New York City's already admirable water supply has just received another layer of protection. After a decade of development, six years of construction, and one year of testing, the world's far and away largest municipal ultraviolet water purification system has been officially opened.

The 270,000 square foot, $1.5 billion Catskill/Delaware facility uses UV light to kill off cryptosporidium and giardia, two microorganisms that can cause gastrointestinal illness. The New York Department of Environmental Protection says that both are already at very low levels in the city's water supply, due to previous efforts to protect water sources, but UV treatment will be effective in taking care of any that is present. The facility, located in Mount Pleasant and Greensburgh, New York, employs 56 separate UV units containing 210 lamps each.

Every day, the plant will process between 800 and 1400 million gallons of drinking water piped in from the Kensico Reservoir, delivering it to approximately 9 million people in both the five boroughs and towns upstate. The facility has a total capacity of 2.w billion gallons a day, which is more than triple the capacity of the next-largest UV treatment facility, which is currently under construction in Los Angeles.

How does UV water sterilization work? The UV-C radiation produced by the lamps destroys the DNA of the bacteria in the water, causing them to lose their ability to reproduce. The now-sterilized microorganisms remain in the water but pose no threat to humans. It doesn't work on dissolved organics or inorganic compounds in the water—meaning that if there's some sort of chemical contamination in the water, treating it with UV light doesn't remove that potential hazard.

Though the new facility is obviously much larger, the concept is similar to hand-held water purification wands, such as Steripen, marketed to backpackers and travelers to regions of the world lacking adequate sanitation. I can testify from personal experience, having treated and drank well water in some decidedly dodgy parts of Asia, that it's an effective technique.

Touting the facility, Deputy Mayor for Operations Cas Holloway said, "New York's water is the best in the world, and now every gallon that travels from the upstate watershed to the city will be treated with ultraviolet light. This long term investment will ensure that New Yorkers can rely on their fresh, clean, great-tasting water supply for generations to come."

That is, of course, assuming that climate change and fracking don't disturb that critical water supply. As NRDC's Eric Goldstein points out, both are threats to the long term future of NYC's municipal water. But in the short term, the facility adds yet another layer of protection to what is already one of the best muni water systems in the world.