# Delaware Aqueduct

41°16′56″N 73°40′04″W﻿ / ﻿41.282317°N 73.667908°W﻿ / 41.282317; -73.667908
The Delaware Aqueduct is an aqueduct in the New York City water supply system. It takes water from the Rondout, Cannonsville, Neversink, and Pepacton reservoirs on the west bank of the Hudson River through the Chelsea Pump Station, then into the West Branch, Kensico, and Hillview reservoirs on the east bank, ending at Hillview in Yonkers, New York.
Built between 1939 and 1945, the Delaware Aqueduct carries about half of New York City's water supply of 1.3 billion US gallons (4,900,000 m$^3$) per day. At 13.5 feet (4.1 m) wide and 85 miles (137 km) long, it is the world's longest tunnel.

## Reservoirs and watersheds

The Delaware Aqueduct carries water from the 95-square-mile (250 km$^2$), 49.6-billion-US-gallon (188-million-cubic-metre) watershed using the Rondout, Cannonsville, Neversink and Pepacton reservoirs with the Delaware and Neversink tunnels. (The latter three reservoirs are within the Delaware River watershed. Rondout is considered by the New York City Department of Environmental Protection (NYCDEP) to be part of the Delaware system despite being firmly within the Hudson River watershed.)
Combined, the four reservoirs account for 1,012 square miles (2,620 km$^2$) of watershed and 320.4 billion US gallons (1.2 billion cubic metres) of capacity, 890 million US gallons (3.4 million cubic metres) of which goes to the city — half of daily demand. All this water is fed from the Rondout to West Branch Reservoir in Putnam County (part of the Croton River watershed, which includes the flow of the upstream Boyds Corner Reservoir), then to the Kensico, and Hillview reservoirs in southern Westchester County, before continuing on to distribution within New York City.

## Leak problems

Leaks were first discovered in the Delaware Aqueduct in 1988, with water losses up to 36 million US gallons (140,000 m$^3$) per day. The city took many years to analyze the leak problem and devise a solution. In 2010 it announced a plan for a major repair project.

### Repairs

The NYCDEP is building a 2.5-mile (4.0 km) Rondout-West Branch Bypass Tunnel beneath the Hudson River, which will allow it to bypass the leak. Construction began in November 2013. "The number's going to be $1.5 billion to do the entire program to make the fix," said Paul Rush, Deputy Commissioner of the NYCDEP. "About two-thirds of it, $1 billion, will actually go into constructing a bypass tunnel around the location with the most significant leakage in Roseton, and to do additional concrete grouting in the Wawarsing section."
The new bypass tunnel is the largest construction project in NYCDEP's history. Construction of the tunnel, 500 feet (150 m) under the Hudson, was completed in 2019. The project involved digging two shafts measuring 700 and 900 feet (210 and 270 m) deep. To complete the repairs, the aqueduct was supposed to shut down temporarily in 2022, but this was postponed. The shutdown was rescheduled for 2024–2025; completion of the project depends on potential drought conditions and associated demand levels for water from the Delaware system. The northern section of the tunnel was shut down in September 2024. At the time, the closure was planned to last eight months.