The current Water Transmission System can be divided into five major segments as shown in the figure below. Redundancy projects for segments 1 through 4 have been completed. The fifth segment, the Metropolitan Tunnels, represents the next challenge for the MWRA in improving the reliability of this great water system.
MWRA Water Transmission System
Metropolitan Tunnel System (Segment 5)
The Metropolitan Tunnel System includes the City Tunnel (1950), the City Tunnel Extension (1963), and the Dorchester Tunnel (1976). These three tunnels interconnect at Shaft 7 at Chestnut Hill. Together, these tunnels carry approximately 60% of the total system daily demand with no redundancy.
