The Quabbin Reservoir is the largest inland body of water in Massachusetts, United States, and was built between 1930 and 1939. Along with the Wachusett Reservoir, it is the primary water supply for Boston, 65 miles (105 km) to the east, and 40 other cities and towns in Greater Boston. The Quabbin also supplies water to three towns west of the reservoir and acts as backup supply for three others. By 1989, it supplied water for 2.5 million people, about 40% of the state's population at the time. It has an aggregate capacity of 412 billion US gallons (1,560 GL) and an area of 38.6 square miles (99.9 km2).

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).