Mayor Michael Bloomberg triumphantly announced the completion of the second stage of Water Tunnel 3 from a valve chamber 200 feet below Central Park. The project to provide redundancy to Manhattan's water system has been underway since 1970. (Photo credit: NYC Department of Environmental Protection)
Water Tunnel 3 was proposed in 1954 in order to provide backup for the aging Water Tunnel 1, which was completed in 1917. Work began in 1970 on stage one, pictured above in 1978 before concrete was laid. Workers used the "drill and blast" technique to make it through 13 miles of bedrock. (Photo credit: NYC Department of Environmental Protection)
Stage 1 has a diameter 20 to 24 feet — significantly larger than the city's other water tunnels — to accomadate increased capacity. This completed section from 1978 brings water down from a reservoir just north of the city down to Central Park. (Photo credit: NYC Department of Environmental Protection)
This 1978 photo shows a passageway in water tunnel 3 leads to the surface. The diameter of the tunnel decreases and water pressure forces liquid to the surface, 500 feet up. (Photo credit: NYC Department of Environmental Protection)
By 1994, workers started using massive tunnel boring machines to work their way through the bedrock. This photo, from April 21st, 1994, shows the first day the machine was used. (Photo credit: NYC Department of Environmental Protection)
The boring machine creates a smoother tunnel through the ground than the drill and blast technique, meaning less concrete is necessary to create a cylindrical tube, as seen in this 2006 photo of construction in tunnel 3. (Photo credit: NYC Department of Environmental Protection)
Section two of Water Tunnel 3, which was activated this week, runs for 8.5 miles from Central Park down to the rest of Manhattan. (Photo credit: NYC Department of Environmental Protection)
Construction on the tunnels for stage two were completed in 2008, and final preparations — including the construction of riser shafts to bring water to the surface — were finished this year. (Photo credit: NYC Department of Environmental Protection)
This section of Water Tunnel 3 has been lined with a steel structure to support the concrete that will carry the water. (Photo credit: NYC Department of Environmental Protection)
Water Tunnel 3 is one of the largest public works projects in New York City history, but the water system itself is far larger than one tunnel. In the mid 1800s the city decided to import water from reservoirs to the north. Workers here are constructing the second aqueduct to serve the city, which was completed in 1890. It remains in use today. (Photo credit: NYC Department of Environmental Protection)
Work on Water Tunnel 1, designed to serve Manhattan, was completed in 1917. Workers here in 1914 use the drill and blast method 500 feet below the surface to dig through the bedrock. (Photo credit: NYC Department of Environmental Protection)
Water Tunnel 1 was built with incredible capacity. To this day it remains sufficient to serve all of Manhattan. The new tunnel is designed merely to allow for extensive repairs to the older system, which hasn't been taken offline in nearly 100 years. In this photo, construction crews fill the gap between the concrete tunnel and the bedrock with grout. (Photo credit: NYC Department of Environmental Protection)
Significant sections of the Bronx, Queens, Brooklyn, and Staten Island are served by Water Tunnel 2, which was put into service in 1936. Above, crews work in 1931 on a Brooklyn section of the tunnel that's 17 feet in diameter. (Photo credit: NYC Department of Environmental Protection)
This map diagrams the entire system that brings water from the land and mountains north of the city. Several reservoirs — some of which are over 100 miles from the city — hold water that moves south solely with gravity. (Photo credit: NYC Department of Environmental Protection)
The Cannonsville reservoir, located near the New York–Pennsylvania border some 100-plus miles from the city. Completed in 1964, it's the newest of the reservoirs. It holds nearly 100 billion gallons of water and was created by damming the Delaware river and destroying the town of Cannonsville, which sat in the valley. (Photo credit: NYC Department of Environmental Protection)