NYC Water
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NYC Water

Catskill Aqueduct Rehab Reaches the Finish Line

A worker inspects the lining of a siphon pipe that allows the Catskill Aqueduct to carry water under smaller streams along its path.
Workers used specially-designed scaffolding to scrape biofilm off the inside of the aqueduct. Approximately 59 miles of the aqueduct were cleaned.
  • Work crews cleaned about 310,000 feet (59 miles) of the aqueduct’s concrete lining. A naturally occurring and harmless film had built up over the decades and created friction which slowed the travel speed of the water, thereby constricting the capacity of the aqueduct. Historic records indicate the Catskill Aqueduct could carry well over 600 million gallons each day when it was first constructed. More recently, it only carried a maximum of about 590 million gallons. Engineers expect to regain some of that lost capacity because of the cleaning.
  • Skilled workers also removed and replaced 35 blow-off valves connected to the steel-pipe siphon portions of the Catskill Aqueduct. These valves are designed to help drain the aqueduct by discharging its water into local streams, creeks or rivers. The valves connected to the aqueduct were from its original construction, and they were rarely used. They were replaced with new valves and mechanical components to ensure their operability into the future. This part of the project required more than just mechanical skill. The belly of each siphon needed to be pumped dry, and each siphon had to be carefully refilled to prevent air from becoming trapped and harming the structure. The steel pipe siphons, which allow the Catskill Aqueduct to travel under smaller streams along its route, were also repaired during the project.
  • The third core mission of the project was to repair structural defects and leaks at several locations along the aqueduct. The cut-and-cover portions of the aqueduct were known to be leaking at several locations. These leaks were sealed by grouting or by the installation of a special carbon-fiber lining within the aqueduct.
The Catskill Influent Weir in Westchester County.



The NYC Department of Environmental Protection protects public health and the environment by supplying clean drinking water, collecting and treating wastewater, and reducing air, noise, and hazardous materials pollution.

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NYC Water Staff

Drink from the tap, flush the toilet, enjoy New York's waterways—we make sure everything flows according to plan.