At 25 miles (40 km) in length, it is one of the longest aqueduct tunnels in the world.

Water from the 412-billion-US-gallon (1.56×109 m3) capacity Quabbin Reservoir flows through the Quabbin Aqueduct from the northeast side of the Quabbin, up a slope to the Ware River Diversion in South Barre, Massachusetts, down again to the Wachusett Reservoir, and then through a power station near the Oakdale section of West Boylston, Massachusetts.

The water surface at the Quabbin Reservoir is about 524 feet (160 m) above Mean Sea Level (MSL).

Portions of the aqueduct follow the route of the Ware River Railway that was discontinued with the building of the Quabbin Reservoir.

When the Wachusett branch begins to create sufficient suction as it fills, then the Ware River Diversion inlet is closed and water flows from the Quabbin to the Wachusett Reservoir as a natural siphon.