The Wachusett Reservoir is the second largest body of water in the state of Massachusetts. It is located in central Massachusetts, northeast of Worcester. It is part of the water supply system for metropolitan Boston maintained by the Massachusetts Water Resources Authority (MWRA). It has an aggregate capacity of 65 billion US gallons (250,000,000 m3) and an area of almost 7 square miles (18 km2). Water from the reservoir flows to the covered Norumbega Storage Facility via the Cosgrove Tunnel and the MetroWest Water Supply Tunnel. The reservoir has a maximum depth of 120 feet (37 m) and a mean depth of 48 feet (15 m).

The Massachusetts Water Resources Authority (MWRA) is a public authority in the Commonwealth of Massachusetts that provides wholesale drinking water and sewage services to 3.1 million people in sixty-one municipalities and more than 5,500 large industrial users in the eastern and central parts of the state, primarily in the Boston area.