With the current drought in the Northeast, you'd probably be appalled to learn of a pipeline that leaks millions of gallons of water each day. But that's exactly what one of the most important water tunnels in the world, the Delaware Aqueduct in New York State, is doing.

This 85-mile-long water tunnel carries about half of New York City's daily supply of a billion gallons of water from reservoirs in New York's Catskill Mountains, the same reservoirs that feed the Delaware River. The tunnel, built in the 1940s, is 13 feet wide, has concrete, steel-lined walls 8 to 14 feet thick, and lies mainly between 500 and 1000 feet below ground. Over time, breaks have developed in the tunnel, and engineers estimate that between 25 and 36 million gallons of water leaks out per day.

After 10 years of analysis and preparation, a complicated and multi-faceted repair effort is about to get under way, involving drilling, a pilotless submarine, and maybe even work crews sent into the tunnel. One thing's for sure - the repairs won't be done soon enough to help with the current drought situation.