World’s longest tunnel that supplies water to half of New York is being shut for $2 billion fix

“The water will always be there,” said Paul Rush, deputy commissioner for the city’s Department of Environmental Protection. “We’re just changing the mix of water that consumers receive.”

The Delaware Aqueduct, operational since 1944, is the longest tunnel in the world, spanning 85 miles (137 kilometers) and supplying water from four reservoirs in the Catskill region to New York City and other upstate municipalities. It provides about half of the 1.1 billion gallons (4.2 billion liters) consumed daily by over 8 million city residents. However, the aqueduct leaks up to 35 million gallons (132 million liters) of water daily, primarily from a section deep beneath the Hudson River.

Though these leaks have been known for decades, officials faced a challenge: they couldn’t take the aqueduct offline for long periods to conduct repairs. Instead, about ten years ago, they began constructing a 2.5-mile (4-kilometer) bypass tunnel under the river. The new tunnel will be connected during this shutdown, which is expected to last up to eight months. During this time, more than 40 miles (64 kilometers) of the aqueduct from the four upstate reservoirs will be out of service, though a section closer to the city will remain operational. Additional leaks farther north in the aqueduct will also be addressed in the coming months.

Rush noted that the timing of the work was designed to avoid the summer, when water demand is higher. The city has spent years improving other parts of the system, some of which are over a century old, to ensure a reliable water supply during the aqueduct shutdown.

“There’s been a lot of careful planning to ensure alternate water supplies,” Rush said.

To compensate, more water will come from the Catskill Aqueduct and the Croton Watershed, which includes a dozen reservoirs and three lakes in the city’s northern suburbs. However, the increased use of the Croton system could affect the taste of the water due to higher levels of minerals and algae in those reservoirs.

“Some residents may notice a temporary, subtle change in taste or aroma during the repairs,” said DEP Commissioner Rohit Aggarwala. “But just like different brands of bottled water have different flavors, so do our various reservoirs. A change in taste doesn’t mean there’s an issue with the water.”