How does a city as big as New York provide enough water not just for drinking, but also for bathing and laundering? New York needs 1.3 billion gallons of water a day.
The answer is that it takes a wonder-of-the-world kind of engineering feat involving two tunnels that are now so old, they're leaking. Nobody knows how long they can last.
And so, an urgent project is under way beneath the city streets: construction of water Tunnel No. 3. It's one of the biggest public works projects on earth - 60 miles long - and when it's finished, it will have taken 50 years to build and cost $6 billion dollars.
As reports, it all starts in upstate New York with a series of mountain reservoirs. There are watershed areas 100 miles north of New York City, with reservoirs at such high elevations that gravity alone carries the water down to the city with enough pressure that no pumps are needed.
But once the water gets to the city, it flows down into those two aging tunnels that have never been repaired or even fully inspected.
The city needs to get Tunnel No. 3 on line before there's trouble.
Work on the new water tunnel has been going on since 1970, but it's far from finished. Mike Greenberg, who used to be in charge of the project, took 60 Minutes on a tour of one section under construction. The ride down, in a steel cage called the Alimak, would take four minutes. For some people, there's a fear of depths similar to a fear of heights.
60 Minutes went down almost 600 feet below ground, the equivalent of a 60-story skyscraper. But Greenberg said the change in air pressure would be imperceptible: "Down here, it's a little more because you're lower. But you don't notice the difference."
Greenberg says the temperature is usually about 50 degrees: "We call it our air conditioner in the summer and our heater in the winter."
OK. It's not too cold, not too hot. And breathing is easy. But there's a lot of water.
"Is it leaking?" asks Stahl. "I mean, this can't be good."
"This tunnel is actually a very dry tunnel during excavation," says Greenberg. "There's always some water coming through the rocks. Not to worry."
Water Tunnel No. 3 is so complicated, vast and deep underground, it's been compared - in terms of engineering feats - to the Brooklyn Bridge and the Panama Canal. Officials here, like Mayor Michael Bloomberg, consider completion of the tunnel vital to the city's future. "You have to pray that we get a third tunnel before anything bad happens," says Bloomberg.
60 Minutes met Bloomberg in one of the new tunnel's valve chambers – built a mere 25 stories below ground to withstand a nuclear blast. It's designed to give water Tunnel No. 3 a flexibility the old tunnels don't have.
"As I understand it, this will provide a way to shut off one section, and repair it and examine it," says Stahl.
"Right," says Bloomberg. "The valves to turn off are here. In the old tunnels, they put the valves down in the tunnel so you couldn't get to them. … You can walk around them. You can work; you can close it off at both ends."
There's never been any maintenance on the two existing tunnels because they haven't been able to close the valves. Why?
"Because they're afraid that if you closed them, what would happen if you couldn't re-open it? Supposing a valve froze closed? You couldn't get it open again," says Bloomberg. "That's one of the fears."