New York City Water Tunnel No. 3 is a water-supply tunnel forming part of the New York City water supply system. It is being built by the New York City Department of Environmental Protection (NYCDEP) to provide New York City with a third connection to its upstate water supply. The tunnel will serve as a backup to Water Tunnel No. 1, completed in 1917, and Water Tunnel No. 2, completed in 1936. Water Tunnel No. 3 is the largest capital construction project in New York City history. Construction began in 1970. Portions of the tunnel were placed into service in 1998 and 2013 and the remaining sections are expected to be complete by 2032. The complete tunnel will be more than 60 mi long, travel 500 ft below street level in sections, and will cost over $6 billion.

Stages

One

The project was authorized in 1954 and imagined as "the greatest nondefense construction project in the history of Western Civilization". The city determined that it needed a third water tunnel so that Tunnels 1 and 2 could be closed for inspection and repairs. Stage One construction of Tunnel 3 began in 1970 and completed in 1993. This portion was put into service in 1998 and cost about $1 billion. This first section was bored through bedrock between 250 and 800 ft underground, using drilling and blasting techniques. Section one is 13 mi long and starts at Hillview Reservoir in Yonkers, New York then crosses under Central Park in Manhattan, to reach Fifth Avenue at 78th Street. From there it runs under the East River and Roosevelt Island into Astoria, Queens. It is a concrete-lined tunnel that is 24 ft in diameter and reduces to 20 ft in diameter before connecting to 14 vertical shafts.

Two

Stage Two was built using tunnel boring machines and comprises two sections. The Brooklyn and Queens section runs 10 mi and begins in Red Hook, Brooklyn, where it connects to the Richmond Tunnel for Staten Island. It passes through Park Slope, Bedford-Stuyvesant, and Bushwick before reaching Maspeth, Queens. From Maspeth it runs through Woodside and Astoria, where it connects to the end of the Stage One section. The Brooklyn section is 16 ft in diameter, and the Queens section is 20 ft. The Manhattan section is 10 ft in diameter and runs for 9 mi. It begins at a valve chamber in Central Park, runs south along the west side of Manhattan, and curves around the southern end of the island to come partway through the Lower East Side. A spur of the Manhattan tunnel begins on the west side at approximately 34th Street, goes to the east side and then turns north under Second Avenue to about 59th Street. The tunnel itself was completed in 2008, and after the construction of seven riser shafts was completed, this section of the tunnel opened in 2013. Two additional riser shafts, each over 700 ft deep, are under construction in Queens as of 2022.

Three

What used to be called Stage Three is now being referred to as a separate project, the "Kensico–City Tunnel". It will be 24 ft in diameter, running from the Kensico Reservoir in Westchester to the Van Cortlandt Valve Chamber complex in the Bronx.

Four

Stage Four is a proposed tunnel that would start at the Hillview Reservoir in Yonkers, pass through the eastern Bronx and then through Queens, where it would eventually meet the Stage Two section.

Valve chambers

The largest valve chamber is in Van Cortlandt Park. It is built 250 ft below the park surface. It controls the flow of water from the city's Catskill and Delaware systems. These systems provide 90 percent of the city's current drinking water. The Van Cortlandt Park Valve Chamber is 620 ft long, 43 ft wide and 41 ft high. The complex has nine vertical shafts; and two manifolds. Each manifold is 560 ft long and 24 ft in diameter and is currently in operation. Additional, though smaller, valve chambers are in use under Central Park at 79th Street, under Roosevelt Island, and in Jackson Heights.

Deaths

Since 1970, when construction on the tunnel began, twenty-four people have died in construction-related accidents. The deaths have included twenty-three workers and a 12-year-old boy, Don-re Carroll, who fell 500 ft to his death down a riser shaft while exploring uncapped water pipes in the Bronx. No deaths have occurred since 1997.

Construction progress

In 2002, New York City mayor Michael Bloomberg made completion of the tunnel a priority, and set a goal date of 2021. Commissioner Christopher O. Ward helped move this project along for the Mayor. A New York Times report in 2016 stated that mayor Bill de Blasio was postponing completion of the project indefinitely, but he subsequently stated that this was a miscommunication between his press office and the Times, and that the completion date was actually being pushed up to 2020. In 2017 De Blasio authorized city expenditures of $300 million for Tunnel No. 3, with an expected project completion date of 2025. Work on the final shafts for the tunnel began in 2021. In September 2022 NYCDEP Commissioner Rohit Aggarwala stated that following the construction of the two deep riser shafts in Brooklyn and Queens, the Tunnel No. 3 project will be completed in 2032.