New York City's water supply system is one of the most extensive in the world. During the last century and a half, the system has expanded to keep pace with the City's rapid development. The New York City Department of Environmental Protection (DEP) maintains this vast and complex system and ensures that the water supply is consistently pure, tasty and plentiful.

Water supply

The high quality of New York City's water is world renowned. DEP operates and maintains the City's three upstate reservoir systems and each day delivers 1,350 million gallons of water to eight million City residents through a complex network of pipes, aqueducts and tunnels. The system also supplies over 100 million gallons of water a day to another one million customers in nearby counties. Together, the Croton, Catskill and Delaware watersheds cover nearly 2,000 square miles.

Located 40 miles from New York City, the Croton System is the City's first and oldest water supply outside the City borders. Before the Croton System was built, New Yorkers drew their water from local wells, ponds and streams. The Croton System began operating in 1842 and initially provided 60 million gallons of water a day. Today, it provides about 10 % of the City's drinking water.

The Catskill Water Supply System, constructed between 1907 and 1927, now delivers about 40% of the City's water. It includes the Ashokan and Schoharic Reservoirs, which are situated west of the Hudson River about 100 miles north of the City. Water is conveyed through the Catskill Aqueduct to the Kensico and Hillview Reservoirs.

The third major component of the City's water supply system is the Delaware System. At its farthest point, the Delaware System is 125 miles northwest of the City. Completed in 1967, it is the newest and largest of the City's three systems and furnishes about 50% of the City's water. Although work began on this water supply system in 1936, construction was interrupted twice: first by litigation and then by the advent of World War Il. Water is conveyed to reservoirs through the Delaware Aqueduct. Listed in The Guinness Book of World Records as the longest tunnel in the world, the aqueduct has a diameter of 13 feet 6 inches, and a length of 85 miles.

Water distribution

Water flows toward the City through three large aqueducts. Water from the Croton System, which primarily serves the Bronx and northern Manhattan, passes through the Croton Aqueduct to the Jerome Park Reservoir in the Bronx. Water from the Catskill and Delaware Systems travels through Hillview Reservoir in Yonkers and enters two large tunnels, Water Tunnels No. 1 and 2, with diameters ranging from 11 to 17 feet. These tunnels connect to a 6,000-mile underground network of water mains that carries drinking water to buildings throughout the City. The water rises from the deep underground tunnels through shafts, to a level just below the street where they connect to the City's water mains. The mains range from 6 inches to 84 inches in diameter.

The New York City water distribution system relies almost entirely on gravity, with pumping required for only the most elevated areas of the City. From the Hillview Reservoir, 295 feet above sea level, water travels through the distribution system with sufficient pressure to reach the sixth floor of most buildings through gravity alone. Some of the pipes still in use are more than 100 years old. A ten-year water main replacement program is currently in progress, with almost two million feet of pipe already replaced or under construction.

Water tunnel n°1 & n°2

Completed in 1917, City Tunnel No. 1 stretches 18 miles, originating at a reservoir in Yonkers and running through the Bronx, Manhattan and into Brooklyn. The tunnel is 15 feet in diameter and diminishes in steps to 11 feet at its terminus in Brooklyn. Tunnel No. 1 has been in continuous use since it went into service in 1917.

The 20-mile long Tunnel No. 2 went into service in 1938 as the City developed eastward from the Bronx and Manhattan. It is 17 feet in diameter, except for a portion of the tunnel between the two southernmost shafts where the diameter is 15 feet. Like Tunnel No. 1, Tunnel No.2 has been in continuous use since it was put into service.

Connected to Tunnel No. 2 is the five-mile-long Richmond Tunnel, through which Staten Island's water supply flows. This tunnel is 10 feet in diameter and runs beneath Upper New York Bay. The Richmond Tunnel was built in anticipation of population growth on Staten Island. The Silver Lake Storage Tanks, which replaced the Silver Lake Reservoir, are the world's largest underground storage tanks. The tanks, placed side by side, each hold 50 million gallons of water.

Water Tunnel No. 3

In 1954, New York City recognized the need for a third water tunnel to meet the growing demand on the more than 150-year old water supply system. Planning for Tunnel No. 3 began in the early 1960s and actual construction began in 1970. While Tunnel No. 3 will not replace Tunnels No. 1 and No. 2, it will enhance and improve the adequacy and dependability of the entire water supply system and improve service and pressure to the outlying areas of the City. It will also provide the opportunity for the New York City Department of Environmental Protection to inspect and repair Tunnels No. 1 and No. 2 for the first time since they were put into service.

In a design departure from the two existing tunnels, valves which control the flow of water will be housed in large underground valve chambers, making them accessible for maintenance and repair. The valves for Tunnels No. 1 and 2 are at the tunnel level and are inaccessible when the tunnels are in service. When Tunnel No. 3 is completed, it will include four large underground valve chambers, numerous riser shafts with riser valve and distribution chambers and surface access facilities. Three of the four valve chambers have already been built to allow the connection of future stages of the tunnel without removing the water or taking any other stage of the tunnel out of service.

The largest of the valve chambers is the Van Cortlandt Park complex. Built 250 feet below the surface, it will control the daily flow of water from the Catskill and Delaware water supply systems. These systems provide 90 % of the City's drinking water. The Van Cortlandt Park Valve Chamber is 620 feet long, 42.5 feet wide and 41 feet high. The complex also contains nine vertical shafts, two manifolds, each more than 560 feet long and 24 feet in diameter, and 34 steel-lined lateral tunnels, each more than 100 feet long. Pressure and flow are controlled through a series of valves and flowmeters.

Stages o f development

Water Tunnel No.3 is being completed in four distinct stages of construction:

Construction technology

Construction of Stages 2, 3 and 4 will be greatly accelerated by use of a tunnel boring machine (TBM), never before used in City Tunnel No. 3. A TBM has been lowered in sections and assembled at the bottom of the shaft. The TBM replaces conventional drilling and blasting methods used during the construction of Stage 1. It is expected that the improved technology will allow tunnel workers to excavate at an average of 70 feet per day, more than three times the rate attained using explosives. Another important advantage to using the TBM is that there is less damage to the rock at the point of excavation and reduced surface noise.

The future

Water Tunnel No. 3 is by far the largest construction project in New York City's history. When completed, it will extend 60 miles through Westchester County, the Bronx, Manhattan, Queens and Brooklyn. The completion of City Tunnel No. 3 will allow New York City to:

• increase delivery reliability to meet the growing demand in the eastern and southern areas of the City which are the furthest from Tunnels No. 1 and 2;
• reduce the demands on Tunnels No. 1 and 2 during peak flow periods
• permit New York City to drain, examine and rehabilitate Tunnels No. 1 and 2, and
• provide alternate delivery in the event service is disrupted in either of the other two tunnels.

Completion of Water Tunnel No. 3 will ensure the reliability of New York City's water delivery system well into the 21st century.

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