Preparations Continue for Closure of Tunnel Supplying Half of City’s Drinking Water

You may not feel it, but major developments are afoot in the city’s water supply.

New York City is preparing to close down a massive—and leaking—aqueduct which delivers over half of the city’s drinking water from upstate reservoirs, more than 120 miles to the north.

The billion-dollar, multi-year repair work on the Delaware Aqueduct is the “central component” of the city’s Water for the Future program, which “aims to ensure clean, safe and reliable drinking water for future generations of New Yorkers.”

On Friday, the city announced that blasting had begun in Wappinger, N.Y., on the Dutchess County side of a new tunnel that will permanently bypass a leaking section of the aqueduct.

The 85-mile long Delaware Aqueduct conveys drinking water from four major reservoirs in the Catskill Mountains -Cannonsville, Neversink, Pepacton and Rondout- to the city’s water distribution system.

The city says that, on average, the Delaware Aqueduct provides more than half of the approximately 1 billion gallons of drinking water consumed by New Yorkers every day. The aqueduct, reportedly the world’s longest continuous tunnel, was constructed between 1939 and 1944 and crosses Ulster, Orange, Dutchess, Putnam and Westchester counties.

New York City’s water supply system is used by more than 9 million people, including 8.4 million in the five boroughs, along with residents of Ulster, Orange, Putnam, and Westchester counties.

City water comes from the Catskill, Delaware, and Croton watersheds.

Leaking Millions of Gallons Per Day

The Department of Environmental Protection, which manages the water supply system, has been monitoring two leaks in the Delaware Aqueduct since the 1990s. The leaks—located in Newburgh and Wawarsing—release a combined 15-35 million gallons a day, “depending on the rate of flow inside the aqueduct.”

To address the leaks, DEP has begun construction of a 2.5-mile bypass tunnel that will run 600 feet below the Hudson River, from Newburgh to Wappinger. The bypass tunnel, which is scheduled for completion in 2021, will convey water around the leaking portion of the Delaware Aqueduct in Newburgh.

DEP spokesman Adam Bosch told NYER that the aqueduct would be shut down for about eight months in 2021, in order to drain it and connect it to the bypass.

What Will Happen When the Delaware Aqueduct is Closed?

Delaware Aqueduct bird’s-eye view. Click here for a larger version.
Delaware Aqueduct bird’s-eye view. Click here for a larger version.

The city says that it has developed a “portfolio” of projects that “will ensure New York City has high-quality and reliable drinking water while the aqueduct is out of service.” This portfolio includes rehabilitating water supply sources used by the city in the past.

The 74-mile-long Catskill Aqueduct, which delivers water from the upstate Ashokan and Schoharie reservoirs, will undergo a repair and rehabilitation project starting in 2016.

The city plans to increase the tunnel’s capacity by approximately 30-40 million gallons of water each day.

For additional water supplies, DEP will also rehabilitate the Queens Groundwater System, formerly the Jamaica Water Supply, which will “sustainably provide more than 33 million gallons of water a day in southeast Queens”.

Groundwater in Queens? Is it safe to drink?

DEP has “committed to using proven technologies to ensure these wells produce high-quality water that meets or exceeds all water quality standards”. The Queens Groundwater System consists of 68 wells at 48 separate well stations.

Another highly complex and expensive project, the new Croton Water Filtration Plant, is entering its final stage of construction in the north Bronx. The city says testing of the filtration system and water lines is nearly complete.

Once online, the filtration plant will allow New York City to again use water from reservoirs in Putnam and Westchester counties that are part of the Croton System. DEP says this will provide nearly 300 million gallons of “high-quality” water each day.

And New Yorkers will have to start thinking more seriously about water conservation.

Between now and the shutdown of the Delaware Aqueduct in 2021, DEP will implement several initiatives to reduce water consumption in the city by as much as 50 million gallons a day.

Water conservation tools –like activation buttons on spray showers- will be rolled out in city parks and public schools. The city is also developing incentives to encourage water conservation in private homes and hotels.

Cool Photos of the Just Rehabbed 123-Year-Old New Croton Aqueduct

New York City has released photos today of this critical—and historic—piece of our water supply infrastructure.

The city also provided some great detail on why the New Croton Aqueduct is so significant. The Department of Environmental Protection says that the $177 million rehab project is a “key milestone towards reactivation of the Croton Water Supply System, which can provide between 10 and 30 percent of the city’s daily water needs.”

More Information from the City’s Release:

The Aqueduct was originally placed into service in 1890 and is a 33-mile-long, 13-foot-diameter, brick-lined tunnel that was engineered to convey by gravity up to 290 million gallons of drinking water each day from the New Croton Reservoir in Westchester County to Jerome Park Reservoir in the Bronx.

The Aqueduct begins just below ground level and reaches a depth of roughly 400 feet.

The New Croton Aqueduct conveys water from the City’s oldest collection of upstate reservoirs in Westchester and Putnam Counties, the Croton watershed, to the in-city drinking water distribution network. For more than 150 years the system provided unfiltered drinking water to the city, first through the Old Croton Aqueduct, which was built in 1842, and then the New Croton Aqueduct.

However, as population density increased around the Croton reservoirs, water quality in the system diminished and, in the late 1990s, DEP stopped using Croton Water for in-city distribution and began planning the construction of a filtration plant. With the system taken off-line and the Aqueduct drained of water, DEP conducted an extensive inspection of the tunnel and began plans for repairs.

Water for New Yorkers of the Future

A major component of the project was the connection of the Aqueduct to the Croton Water Filtration Plant in the Bronx.

A large concrete plug, 58 feet long and 12 feet wide, was built within the Aqueduct to direct the water through a new tunnel to the filtration plant. Once the water has gone through the filtration process, it travels through a separate tunnel back to the Aqueduct, downstream of the concrete plug, and towards the distribution network. The filtration and mechanical systems within the Croton Plant are currently being tested with water provided through the New Croton Aqueduct.

The completion of the Croton Filtration Plant and the reactivation of the Croton drinking water supply system will play important roles in the future as DEP repairs leaks in the Delaware Aqueduct, which currently supplies more than 50 percent of the city’s daily water needs.

Last year DEP began building two vertical shafts on opposite sides of the Hudson River in Orange and Ulster Counties. The shafts will be used by workers to build a bypass tunnel around a leaking portion of the Delaware Aqueduct, roughly 600 feet below ground level. Once that bypass tunnel has been built, DEP will temporarily shut down the Delaware Aqueduct in 2021 to make the necessary connections.

The Croton system will be critical in ensuring that DEP can continue to meet the city’s drinking water needs during the shutdown of the Delaware Aqueduct. It will also help to supplement the city’s water supply during future drought conditions.


DEP manages New York City’s water supply, providing more than one billion gallons of water each day to more than nine million residents, including more than eight million in New York City.

The water is delivered from a watershed that extends more than 125 miles from the city, comprising 19 reservoirs and three controlled lakes. Approximately 7,000 miles of water mains, tunnels and aqueducts bring water to homes and businesses throughout the five boroughs.


And for all you New York City water system fanatics, here are some details on the actual work on the aqueduct:

Rehabilitation work included re-grouting the brick lining of the tunnel, upgrading 34 shaft site connections that allow crews to access the tunnel from ground level, and repairing valves and pumps that allow certain Westchester communities to pull water from the Aqueduct.

Five historic gatehouses located at ground level along the route of the Aqueduct were also restored.

Due to a limited number of access points, and restrictions on the size of the equipment that would fit through them, much of the machinery was taken apart and lowered by crane though the shafts hundreds of feet down to the Aqueduct, where it was reassembled.

The inspection of the Aqueduct began in 1996 and included the use of ultrasonic stress waves, ground penetrating radar, and diamond core test drilling to determine the permeability and strength of the tunnel lining and surrounding bedrock. A remotely operated vehicle inspected the portion of the tunnel that runs under the Harlem River, which was not dewatered.

Overall, the Aqueduct was found to be in good condition, with some areas requiring sediment removal, the repair of cracks in the tunnel lining, and brick and mortar repointing and replacement.

Rehabilitation work commenced in 2004 and was completed in 2013. The interior of the Aqueduct was power washed and where investigations showed that a void may be present behind the tunnel lining, a series of grouting injections was made to ensure the stability of the tunnel.

The lining of the tunnel is made up of more than 163 million bricks and portions were repointed and secured with new grouting to reduce friction in the tunnel and keep groundwater from seeping in. Additionally, a new 10-foot diameter shaft cap was installed at the Aqueduct’s terminus in upper Manhattan.

Work also included the upgrade of existing connections to the Aqueduct, including shafts and pumps, for the Villages of Briarcliff Manor, Tarrytown, and Sleepy Hollow. The New Croton Aqueduct serves as a backup water supply for these villages, which primarily rely on the Catskill Aqueduct.

In addition, the towns of New Castle, Ossining, and Pelham, the villages of Pleasantville, Ossining, Irvington, Ardsley, Bronxville, Dobbs Ferry, Hastings-on-Hudson, Pelham Manor, Pelham, Tuckahoe, and the City of New Rochelle also have connections that allow them to use water provided through the New Croton Aqueduct.