Plumbers in Cambridge, MA

Fresh Pond water, with the MWRA held in reserve

Cambridge has run its own water system since 1865. Rain and runoff collect in the Hobbs Brook and Stony Brook reservoirs, which hold 3.1 billion gallons between them, then flow about eight miles through the gravity-fed Stony Brook Conduit to Fresh Pond, which holds another 1.3 billion. After treatment at the Sullivan plant, more than 200 miles of city pipe carry it to over 100,000 residents.

Three emergency interconnections to the MWRA give the city a fallback. In 2024 Cambridge drew on MWRA water for five days during an emergency repair at the treatment plant, and when the MWRA's own main failed in May 2010, Cambridge kept full service. Drought can force the switch too: on October 1, 2026, the Boston Globe reported Hobbs Brook at roughly 20% of capacity, with the city set to begin buying MWRA water if the level reached 15% and the City Council shifting $2.25 million to cover the cost.

What this means for you is mostly about phone numbers. Anything on the public water side, from a break in the street to a question about your service pipe, goes to the Water Department, not the MWRA. The same department runs Cambridge's cross-connection and backflow program (617-349-4025, backflow@cambridgema.gov) and recommends a backflow preventer on any home lawn sprinkler system.

Combined sewers, Alewife Brook and the backwater valve rule

Cambridge's combined sewer system is more than 150 years old. The city still maintains 43 miles of combined sewer mains, and the Conservation Commission's March 2026 minutes put separation at about 55 to 60 percent. When a heavy storm overloads the pipes, the excess leaves untreated through seven outfalls that remain open: four on Alewife Brook and three on the Charles.

Separating sewers is slow, costly work. In West Cambridge, the Alewife separation split storm and sanitary flow across 211 acres and added a 3.5-acre wetland, at a cost of more than $200 million; one of its stated aims was to curb street flooding and sewer and stormwater backups on public and private property. The next phase is a draft plan that Cambridge, Somerville and the MWRA submitted on May 1, 2026, calling for two storage tanks holding 3 million gallons along Alewife Brook, at about $340 million and 13 to 18 years of construction once approved.

Because those fixes are years away, the protection that counts is inside the house. City regulations and the state plumbing code (248 CMR 10.15) require a backwater valve on every fixture and appliance installed below the roadway, and putting one in takes an Inspectional Services permit; the city recommends a licensed plumber for the job. If your basement has a toilet, shower, laundry or a rental unit and no valve, ask a plumber to look before the next big storm. Our sewer line repair page covers how to tell a clog in your own line from a storm backup.

Old houses, three-deckers and towers in one city

The Census gives Cambridge a median year built of 1950, yet 47% of its roughly 54,840 housing units date from 1939 or earlier. The mix of building sizes is wide: 17% of homes are in three- and four-unit buildings, 12% in two-family houses, and 27% in large complexes of 50-plus units. Only about one home in ten is a detached single-family house.

Mid-Cambridge shows the layering in a single neighborhood. The city's Historical Commission describes it as 19th-century suburban houses, in styles running from Greek Revival and Italianate to Queen Anne and Colonial Revival, plus early-20th-century three-deckers and apartment buildings, and mid-century townhouses and towers. Each layer comes with its own plumbing, from original cast-iron stacks and aging supply pipe in the older houses to shared risers and mains in the big buildings. With about two-thirds of households renting (66.5%), many repairs are decided by a landlord or condo association rather than the person who first spots the leak.

Lead service lines: the last fifth

As of November 2024, the Water Department said it had removed 80% of the city's lead service lines since 1996 and was working through the remaining 20%, with the aim of finishing years ahead of the federal 2037 deadline. Owners of lines recorded as lead, galvanized or unknown were mailed letters. The department also publishes a list of service materials by address, with lead lines highlighted, and will send someone to confirm the pipe if you call 617-349-4770 or email CWD@cambridgema.gov.

Know the cost split before you sign anything. Cambridge replaces the public section, from the main to your property line, at no charge, and the owner pays for the stretch from the property line to the meter; when both are replaced at the same time, the city says it typically ends up covering 75 to 80 percent of the total. Residents can also get their tap water tested for lead for free, and more than 700 such tests were done in 2024. Our guide to lead pipes walks through the private-side work.