Hard-hat workers are toiling deep underground, 55 stories beneath the Hudson River, to eliminate gushing leaks in an aging tunnel that carries half the city's water supply over 85 miles from Catskill Mountain reservoirs. Using a cylindrical, space-rocket-size borer, they are carving through solid rock to create a 2.5-mile bypass tunnel around the worst of the leaks.

When they finish the $1 billion tunnel in 2022, the entire Delaware Aqueduct will be shut down for months to prepare for the diversion. And if they do it right, New Yorkers turning on their faucets will never even notice.

"It's really the largest and most complex water tunnel repair that the city of New York has ever done," said Vincent Sapienza, commissioner of the city Department of Environmental Protection. "There's a lot of moving parts that we've been wrestling with for several years now."