Somerville, Massachusetts
Somerville Water Quality
MWRA reservoir water through some of the oldest mains in the region. Somerville's 2025 report shows a lead replacement program close to done: 372 lead services replaced and 24 known ones left.
24 known lead service lines left at the start of 2026, after 372 replaced.
The short answer
Somerville drinks MWRA water from the Quabbin and Wachusett Reservoirs, disinfected with chloramine. Its 2025 lead result was 3.92 ppb at the 90th percentile (MWRA-wide 5.96), with one of 20 homes over the 15 ppb action level.
The bigger story is the pipe: the City has replaced 372 lead services and had 24 known lead services left at the start of 2026. If yours is one of them, the City's program comes first. For everyone else, older in-house plumbing and chloramine taste are the practical questions — and a tap test answers both.
Get a free test
Tell us your Somerville address. We confirm coverage first, then schedule a licensed technician to test at your tap — no charge, no obligation.
What filtration does — and does not
Softening, carbon and reverse osmosis solve different problems. A filter is not a substitute for replacing a lead service line.
Where Somerville water comes from
The same reservoirs as Boston, through older city pipes.
Quabbin and Wachusett Reservoirs
Somerville buys treated water from the MWRA, whose sources are the Quabbin and Wachusett Reservoirs in central and western Massachusetts.
Treated at the Carroll plant
MWRA's John J. Carroll Water Treatment Plant in Marlborough disinfects with ozone and UV, adds fluoride, adjusts pH and alkalinity to reduce lead corrosion, and finishes with monochloramine.
Then 125 miles of Somerville main
Water enters through seven MWRA master meters into about 125 miles of city main, much of it installed in the late 1800s to early 1900s.
What the 2025 Somerville report actually says
Limits are fixed. Results are from MWRA's 2025 Drinking Water Test Results for Somerville, including the City letter — system-level figures, not a reading at your tap. A later report supersedes them.
Lead — 3.92 ppb at the 90th percentile
Somerville's 2025 round of 20 homes: 3.92 ppb at the 90th percentile, below the 15 ppb action level. The MWRA-wide figure was 5.96 ppb.
One home over the action level
The range ran from 0.113 to 142 ppb. One household exceeded the action level, and its lead service was replaced with copper through the City's program in 2025.
372 lead services replaced; 24 known left
After elevated results in 2020 and 2021, the City used the State Revolving Fund program to replace 63 lead services in 2025 and 372 since the start. At the start of 2026, 24 known lead services remained.
Copper — 83.8 ppb
90th percentile across the same 20 homes (range 7.7–102 ppb), against a 1,300 ppb action level.
TTHM 16.1 ppb · HAA5 15.8 ppb
MWRA's 2025 system averages for disinfection byproducts, against MCLs of 80 and 60.
Monochloramine — 1.99 ppm
MWRA disinfects with chloramine (range 0.02–3.7 ppm, maximum residual 4). That shapes filter choice more than any contaminant on this list.
Somerville next to Cambridge, Boston and Framingham
Across the city line, Cambridge is not an MWRA community at all — it treats its own Fresh Pond supply. Boston drinks the same MWRA water as Somerville, and its autumn 2025 lead result at higher-risk taps was over the action level. Out west, Framingham reported no known lead service lines at all. Same reservoirs, very different pipes.
Where these figures come from
Everything on this page traces to MWRA and the City of Somerville Water and Sewer Department.
- MWRA — 2025 Drinking Water Test Results, with the City of Somerville letter (PDF) — MWRA sources, treatment and detected contaminants; Somerville's lead and copper results, lead service replacement totals, main replacement and coliform compliance.
- City of Somerville — Lead Service Line Replacement Program — the service line inventory lookup and program sign-up.
Matching treatment to the finding
Somerville's report supports checking your service line and a chloramine-aware filter choice — not a default equipment sale.
Look up your address first
The City posts its service line inventory online. If your address shows lead, galvanized or unknown, the City's replacement program is the first call, and a certified lead filter is the stopgap until it's done.
Old houses, old plumbing
Somerville's housing is old, and the service line is only part of the story. Lead solder and brass fixtures inside a house are a separate question that a test at your tap answers.
Chloramine taste: catalytic carbon or RO
Ordinary carbon handles free chlorine better than chloramine. If taste or odour is the complaint, catalytic carbon or reverse osmosis is the right tool.
Hardness: test, do not assume
The report prints no hardness figure, and MWRA water is not usually sold a softener. A tap test settles it before anyone sizes one.
How the free test works
A licensed technician tests at your kitchen tap, walks the plumbing, and tells you which of the findings above applies to your house and which does not. There is no charge and no obligation.
Seamless Home is the licensed contractor of record on the work that follows. Installation is performed by vetted installing partners engaged as our subcontractors, and the workmanship obligation stays with us. Coverage is confirmed per service area rather than promised as blanket availability.
What a water treatment job with us covers
Installation and replacement of whole-home and point-of-use treatment, specified against what your water actually contains.
Sediment filtration
Installation of the first stage that protects everything downstream of it, sized to the service line and the household draw.
Softening
Installation of ion-exchange softening where hardness is the problem, including the drain connection the plumbing code treats as indirect waste.
Carbon filtration
Installation of carbon stages for taste, odour and disinfection by-products, specified from your utility's own water quality report.
Reverse osmosis
Point-of-use installation at the kitchen sink where the target is dissolved solids rather than whole-home flow.
Disinfection
Installation of UV or equivalent treatment where the supply is a private well or is otherwise not continuously disinfected.
System replacement
Replacing equipment that has reached the end of its service life, including the discharge and air gap details an inspector looks at.
This is installation and replacement work, specified from a published water quality report or a test of your supply — not from a sales chart. Coverage is confirmed per service area rather than promised as blanket availability.
What the work actually looks like
Treatment equipment is plumbing. Most of the job is the connection, the drain and the code detail behind it.
Somerville water, answered plainly
Where does Somerville's water come from?+
From the MWRA. Somerville buys treated water from the Quabbin and Wachusett Reservoirs, treated at the John J. Carroll Water Treatment Plant in Marlborough and delivered through seven MWRA master meters into the City's own distribution system.
Does Somerville still have lead service lines?+
A few. Per the City's letter in the 2025 report, Somerville has replaced 372 lead services since its Lead Service Replacement Program began, 63 of them in 2025, and 24 known lead services remained at the start of 2026. The City says it is trying to replace the rest this year and has contacted those addresses.
Is there lead in Somerville tap water?+
In 2025 the 90th percentile among 20 sampled homes was 3.92 ppb, below the 15 ppb action level. One home was over the action level; its lead service was replaced with copper in 2025. Lead can still come from plumbing inside an individual house, which only a test at your tap shows.
How do I check my service line?+
The City of Somerville posts its water service line inventory on its Lead Service Line Replacement Program page, where you can look up an address and sign up for replacement if lead is listed.
Does Somerville use chlorine or chloramine?+
Chloramine. MWRA disinfects with monochloramine, averaging 1.99 ppm in 2025.
Where do these figures come from?+
MWRA's 2025 Drinking Water Test Results for Somerville, which includes the City of Somerville Water and Sewer Department letter. Third-party aggregators are not used. A later report supersedes these figures.
Related resources
Home water purification and treatment
The national service page behind this one.
Learn more →Cambridge water quality
Next door, but its own Fresh Pond supply — not MWRA.
Learn more →Boston water quality
The same MWRA water, and Boston's 2025 lead exceedance.
Learn more →Waltham water quality
MWRA water, no lead lines on file, and a November 2025 coliform finding.
Learn more →All home services
Water, battery, HVAC and solar under one licensed contractor of record.
Learn more →Get a free test at your tap
A licensed technician tests at your kitchen tap and tells you which findings apply to your house — lead from older plumbing, chloramine taste or none of them. No charge, no obligation, and coverage confirmed at your address first.
Get a free test