Waltham, Massachusetts
Waltham Water Quality
All-MWRA water and no lead service lines on file. Waltham's 2025 report is about the pipes in between: a November 2025 coliform exceedance traced to low disinfectant levels at some sample sites.
November 2025: coliform above the 5% monthly limit, Level 1 Assessment filed on time.
The short answer
Waltham buys all of its water from the MWRA, disinfected with chloramine. Its 2024 inventory lists no lead, galvanized or unknown service lines, and the 2025 lead result was 1.92 ppb at the 90th percentile.
The finding to know is in the distribution system: in November 2025 total coliform exceeded the 5% monthly limit, triggering a Level 1 Assessment, which pointed to low disinfectant levels at some sample sites and flushing that stirred up sediment. At the tap, the practical questions are chloramine taste, occasional discolouration and older house plumbing.
Get a free test
Tell us your Waltham 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. Waltham's report does not make the case for a whole-house system by itself.
Where Waltham water comes from
The same reservoirs as Boston, through Waltham's own mains.
Quabbin and Wachusett Reservoirs
The City of Waltham purchases all of its water from the MWRA, whose sources are the Quabbin and Wachusett Reservoirs.
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 170 miles of Waltham main
Water enters through nine MWRA master meters into 170 miles of city main and about 14,000 service connections, with 1,600 hydrants and 3,300 gate valves.
What the 2025 Waltham report actually says
Limits are fixed. Results are from MWRA's 2025 Drinking Water Test Results for Waltham, including the City letter — system-level figures, not a reading at your tap. A later report supersedes them.
Coliform over 5% in November 2025
MWRA and Waltham take 72 samples a month. In November 2025 more than 5% were positive for total coliform, which required a Level 1 Assessment. The City submitted it to MassDEP on time.
What the assessment found
Low disinfectant levels at some sample sites, and hydrant flushing scheduled too close to sampling at nearby sites, which may stir up sediment in the pipes.
No lead, GRR or unknown service lines
Waltham's October 16, 2024 inventory to MassDEP lists none. The statement does not cover lead connectors — goosenecks or pigtails, typically under two feet long.
Lead — 1.92 ppb at the 90th percentile
September–October 2025, 20 homes: 1.92 ppb (range 0.075–2.27), none over the 15 ppb action level. The MWRA-wide figure was 5.96 ppb.
Copper — 94.6 ppb
90th percentile across the same homes (range 6.34–98.5 ppb), against a 1,300 ppb action level.
Monochloramine — 1.99 ppm
MWRA's 2025 average residual (range 0.02–3.7 ppm). TTHM 16.1 ppb and HAA5 15.8 ppb, against MCLs of 80 and 60.
Waltham next to Framingham, Quincy and Cambridge
Framingham also reports no known lead service lines, with a short list of galvanized and unknown lines left to check. Quincy is the other MWRA city on this site with a coliform assessment in its report. Cambridge is different again: its Hobbs Brook reservoirs sit partly in Waltham, but Cambridge treats its own supply rather than buying from the MWRA.
Where these figures come from
Everything on this page traces to MWRA and the City of Waltham Engineering Department.
- MWRA — 2025 Drinking Water Test Results, with the City of Waltham letter (PDF) — MWRA sources, treatment and detected contaminants; Waltham's lead and copper results, the November 2025 coliform Level 1 Assessment, service line statement and system figures.
- City of Waltham — Water Service Line Inventory — the inventory statement and the service material map.
Matching treatment to the finding
Waltham's report supports a chloramine-aware filter choice and a tap test — not a default equipment sale.
Residual and sediment: point-of-use first
The November finding was about disinfectant residual and stirred-up sediment in mains — distribution issues the City addresses. If you notice discoloured water after flushing, run cold water until it clears; a sediment pre-filter helps where it recurs.
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.
Connectors and house plumbing
With no lead service lines on file, remaining lead questions are short connectors and plumbing inside the house — old solder and brass fixtures. A tap test answers them.
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.
Waltham water, answered plainly
Where does Waltham's water come from?+
Entirely from the MWRA. The City of Waltham purchases all of its water from the Quabbin and Wachusett Reservoirs, treated at the John J. Carroll Water Treatment Plant in Marlborough, and delivers it through nine master meters into its own 170-mile distribution system.
What happened with coliform in Waltham in 2025?+
Per the City's 2025 report letter, more than 5% of monthly samples were positive for total coliform in November 2025, which triggered a Level 1 Assessment. The City submitted the assessment to MassDEP on time and found low disinfectant levels at some sample sites, plus hydrant flushing too close to sampling that may stir up sediment.
Does Waltham have lead service lines?+
Waltham's October 16, 2024 inventory to MassDEP states the system has no lead, galvanized-requiring-replacement or unknown service lines. The City notes that statement does not account for lead connectors (goosenecks or pigtails). The City's Water Service Line Inventory page has the detail.
Is there lead in Waltham tap water?+
In September–October 2025 the 90th percentile among 20 homes was 1.92 ppb, with none over the 15 ppb action level. The City also received a MassDEP non-compliance notice for sending those results to the participating residents 39 days after receiving them instead of within 30.
Does Waltham 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 Waltham, which includes the City of Waltham Engineering 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 →Framingham water quality
MWRA water with no known lead service lines.
Learn more →Somerville water quality
MWRA water and a lead replacement program near the finish line.
Learn more →Quincy water quality
MWRA water through old cast-iron mains.
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 — chloramine taste, sediment, older plumbing or none of them. No charge, no obligation, and coverage confirmed at your address first.
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