The Cosgrove Aqueduct, also called the Cosgrove Tunnel, forms part of the water supply system for Boston, Massachusetts, operated by the Massachusetts Water Resources Authority. It is a man-made tunnel connecting the eastern end of the Wachusett Reservoir to the Walnut Hill Water Treatment Plant in Marlborough, and is linked to the MetroWest Water Supply Tunnel.
The tunnel came on line in 1965, when it replaced the Wachusett Aqueduct as the main conduit used to deliver water from the Wachusett Reservoir. It has a capacity of 600 million US gallons (2,300,000 m3) per day.