Until the 1960s, the Weston Reservoir was one of two distribution reservoirs close to Boston, receiving water from the Wachusett Reservoir via the Weston Aqueduct (placed in service in December 1903), which in turn received water from a connection to the Hultman Aqueduct in Southborough. Because of the construction of the water treatment facility at Walnut Hill, the Cosgrove Tunnel was shut down in 2003 in order to make the large piping connection between the new treatment plant and the MWRA's new MetroWest Water Supply Tunnel. The MetroWest Tunnel extends east 18.6 miles (29.9 km) from Walnut Hill to Weston. During that shutdown, the Wachusett Aqueduct was the primary method of transmission of about 240 million US gallons (910,000 m3) of water per day. It remains a backup connection to two underground storage tanks near the Massachusetts Turnpike in Weston as well as the Weston Reservoir.
Walkers extensively use the area around the Weston Reservoir. This reservoir is maintained along with other open distribution reservoirs (Sudbury, Foss, Brackett, Stearns, Norumbega, Waban, Spot Pond, Chestnut Hill and Middlesex Fells) as an emergency backup only. The MWRA's main distribution reservoirs are now covered storage facilities. The Weston Reservoir is now used by grounds crews and the MWRA's Emergency Service Unit for training and storage of emergency trucks and equipment.