New York City's water supply system has been called a marvel of engineering -- the eighth wonder of the world. It covers some 2,000 square miles, runs as deep as 1,100 feet underground and supplies as much as 1.5 billion gallons of water per day to more than nine million people.
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But even at the earliest stages of its journey -- as water trickles down the face of the mountains of the Catskills -- the people in charge of New York's water supply worry about its quality. As these trickles gather momentum and join together into streams, the city's scientists are right there serving as monitors, looking for heavy algae growth and other signs of pollution, including microscopic animals that can cause stomach problems and diarrhea.
Before 1842, New York's water supply consisted of a single fetid pool in lower Manhattan, and water-born disease was common.
Now, after the water flows from hundreds of small Catskill Mountain streams and the Delaware River into 19 upstate reservoirs, it is naturally filtered by rocks and soil. Once it reaches the reservoirs, it is allowed to sit for a while. That is so that impurities in the water can settle to the bottom.
From the reservoir, water is discharged into the city's aqueducts. The New York City Department of Environmental Protection must check the aging upstate aqueducts for leaks. In June, the city sent an unmanned submarine to inspect a damaged 45-mile stretch of the Delaware Aqueduct. Results from the submarine's 16-hour photographic journey are still being studied, but according to officials, the aqueduct has at least two known leaks that spill as much as 36 million gallons of water a day.
The water that does get through then enters the city distribution system. Most cities filter their water at this stage of the process. But New York does not.
"The water that comes into New York City aqueducts is frequently of superior quality than filtered systems, but it also makes it very fragile," said Jim Tierney, the city official in charge of protecting the reservoirs and the region surrounding it, known as the watershed. "It makes protective efforts to keep pollutants out of the water all the more important."
With that in mind, in 1997, city, state and federal agencies and environmental groups reached an agreement designed to protect New York's watershed, which, though comprising just a fraction of the state's total land area, supplies water to half the state's population. "If there's anything you have to protect in New York," Tierney said, "it's this watershed."
The U.S. Environmental Protection Agency has waived the requirement that the city filter much of its water. But the city did not apply for a waiver for water coming from the Croton watershed and must now build a filtration plant. The city is currently reviewing three potential sites for the plant, one in Westchester and two in the Bronx. The plant must be operating by 2010 or 2011, depending on which site is chosen.
New York does treat its water though. Chlorine is added to kill organisms such as Giardia, which can cause diarrhea in humans. At each stage of the journey from here on, chlorine levels will be carefully calibrated and monitored, to make sure there is enough chlorine to kill bacteria and parasites -- but not so much that it makes the water disagreeable.
One part of fluoride per million parts of water goes in to help New Yorkers fight tooth cavities. The city adds orthophosphate to keep lead from leaching into the water, while some of the city’s water also gets a dose of sodium hydroxide to make it less corrosive.
Once water is treated, it enters City Tunnels No. 1 and 2, the main distribution tunnels. Pressure in the tunnels forces water up vertical shafts and into the city's water mains.
If there is a leak in either of these tunnels, there is little the city can do. Sandhogs are digging a 60-mile-long third water tunnel, but construction is not scheduled to be completed until 2020. Until then, engineers cannot shut down the city's two existing tunnels for repair.
"A disaster could happen at any moment, a disaster of epic proportions, or they will get the tunnel built in time. Nobody knows," said Jeff Jones of Environmental Advocates.
From the tunnels, the water branches out into the city’s water pipes. Some of these were first put into service in the 1800s, and as residents of Washington Heights discovered recently, they can burst, shooting geysers 20 feet into the air, turning streets into lakes, flooding basements and leaving hundreds of thousands of dollars of damage in their wake. New York City experiences 600 breaks per year on average, according to the Department of Environmental Protection. Even minor ones can sully the water supply and cause disruptions.
Before the water enters individual homes and buildings, it is tested again at one of the nearly 1,000 sampling stations throughout the city. Tony Speranza is one of 16 Department of Environmental Protection field collectors charged with monitoring water quality to ensure it meets federal and state guidelines. On a recent morning, Speranza's route took him to the corner of Maiden Lane and (aptly) Water Street. Inside an inconspicuous metal box resembling an oversized parking meter was a simple faucet and miniature basin.
First, Speranza disinfected and flushed the tap. Then, he pulled a milk crate filled with specimen containers -- each one labeled and bar-coded -- from the truck that doubles as his roving laboratory. As water gushed into the basin, Speranza checked for telltale signs of contamination.
According to Speranza, even small variances in temperature or conductivity (a measure of metals in the water) can indicate a problem in the system. And curbside sampling is especially important when it comes to monitoring chlorine.
From here, water is carried by service pipes to individual buildings -- and finally to residents' faucets. Officials will check some of this water as well, testing for lead levels. This final point marks the end of an extraordinary journey, one that is powered entirely by gravity.
If there are problems, as people like Speranza certainly know there are, still, as far as he is concerned, "New York City water is the best in the world."