The tunnel will parallel and eventually bypass a long-troubled section of the Delaware Aqueduct, through which New York City receives about half of its 1.1-billion-gallon-a-day water supply. This part of the aqueduct has been leaking up to 35 million gallons of water a day for decades. Officials believe it is irreparable.

If all goes according to plan, the city’s Department of Environmental Protection will shut down the Delaware Aqueduct in October 2022. After the water has drained out, workers will connect each end of the new bypass tunnel to the older aqueduct, plug up the damaged portion permanently and make repairs elsewhere while they have the chance. Five to eight months later, they will reopen the aqueduct.

The Delaware Aqueduct bypass is an approximately $1 billion project that few New Yorkers will ever see, though it affects every New Yorker’s life. City government is still capable of thinking big when it has to — and in the case of the water supply, it must.

From late 2022 through early 2023, the city will compensate for the dry Delaware spigot by relying more on the Catskill and Croton watersheds. The Croton system, by far the oldest of the three, has been shut since 2008, while the city constructs a filtration plant in the Bronx. That should be finished next year.