Cambridge Water Quality

No. Cambridge runs its own supply and its own treatment plant, under public water system identifier 3049000. This is the single most useful thing to know before reading anything about Massachusetts water, because MWRA's figures are the ones that circulate for the whole state and they describe a different system. Cambridge draws from the Hobbs Brook Upper and Lower reservoirs, Stony Brook Reservoir and Fresh Pond — four bodies of water across four towns, storing up to 4.4 billion gallons — and treats all of it at the Walter J. Sullivan Water Purification Facility at Fresh Pond. There is a qualification worth knowing: Cambridge and the MWRA have maintained emergency and backup interconnections since 2013, and in December 2025 Cambridge used a small amount of MWRA water during purification facility maintenance. It is not an MWRA community; it has an MWRA fallback.

Sodium, at 93.5 ppm against a Massachusetts Office of Research and Standards Guideline of 20 ppm, attributed by the report to road salt. It is the only result that exceeds the figure printed beside it. The ORSG is guidance rather than an enforceable limit and there is no violation here, but the guideline exists for a specific group of people — those on physician-directed sodium-restricted diets — and MassDEP uses the same 20 mg/L figure as the trigger for investigating a supply where a resident is on a documented restriction below 1,000 mg a day. Chloride at 167 ppm and total dissolved solids at 323 ppm corroborate the cause. If a household has someone managing sodium intake, this is a conversation for a doctor, and reverse osmosis is the treatment stage that addresses it.

Both, and they answer different questions. The footnote states that an 8-ounce glass contains approximately 22 milligrams of sodium, well within the FDA's very low sodium category — that is a food-labelling threshold applied per serving, and 22 mg per glass does sit inside it. The 20 ppm ORSG in the guidance column of the same table is a concentration for a whole day's water, and MassDEP expresses it on the same 8-ounce basis, which works out near 4.7 mg per glass. So one glass is very low sodium by FDA labelling and 4.7 times the state guidance concentration at the same time, because the two benchmarks were written for different purposes. Two litres a day of Cambridge water carries roughly 187 mg. Neither figure is wrong; only one of them is about sodium-restricted diets.

Because of two treatment choices, and the gap is large: total trihalomethanes at 8.6 ppb in Cambridge against 63 ppb in Worcester, both measured against the same federal MCL of 80. Disinfection byproducts form when a chlorine-based disinfectant reacts with naturally occurring organic matter, so the amount depends on how much organic carbon reaches the disinfection stage and which disinfectant meets it. Cambridge filters through granular activated carbon, which removes organic compounds before disinfection, and maintains its residual with monochloramine, which is less reactive for this purpose. Worcester filters through anthracite and disinfects with free chlorine. Both cities are fully compliant. The difference is chemistry, and it is the reason the right equipment is not the same in two Massachusetts cities forty miles apart.

Almost certainly not, and here the reason is different from the one that applies in Boston or Worcester. Cambridge does not publish a hardness figure; it reports calcium at 18.2 ppm and magnesium at 3.9 ppm, which converts to roughly 62 ppm or about 3.6 grains per gallon — on the boundary between soft and moderately hard, and genuinely harder than Boston or Worcester. So the usual New England argument, that there is nothing to remove, is weaker here. The stronger argument is what softening does: ion exchange trades hardness minerals for sodium, and Cambridge water already reports 93.5 ppm of sodium against a 20 ppm guideline. A softener would push the one out-of-guidance number on the report further out.

Every regulated contaminant in the report is inside its federal or state limit, with no violations recorded. Turbidity, which measures how well the filtration is working, met its treatment technique on 100 percent of samples. What a compliance statement cannot describe is the water at your own tap, and in Cambridge there is one specific reason for that: lead comes from service lines and household plumbing rather than from the source, and although the city has removed 80 percent of its lead service lines since 1996, the remaining 20 percent belong to particular addresses. The 2023 sampling round gave a 90th-percentile lead result of 8 ppb against an Action Level of 15 with no exceedance. That is a good citywide result and it is not a measurement of your building, which is why the city gives away test kits.

Because lead and copper monitoring runs on a multi-year cycle rather than annually, and the report says so in a footnote: results are from the most recent sampling in 2023. A system demonstrating low results is permitted to sample less often. The figures are a 90th-percentile lead result of 8 ppb against a 15 ppb Action Level, individual samples ranging from non-detect to 14 ppb, and no home exceeding the Action Level. Copper's 90th percentile was 0.035 ppm against 1.3. Read them as evidence that the water leaving the plant is not aggressively corrosive, rather than as a current reading at any particular address — and note that Cambridge offers free lead testing to any resident through a kiosk at the purification facility, which answers the address-specific question directly.

The report states that Cambridge and the Northeast region are in a Level 3 Critical Drought, with all non-essential outdoor watering banned under City Ordinance, and that persistent conditions have kept reservoir levels significantly below the fifteen-year average. A Water Ordinance Drought Amendment took effect in April 2025 to comply with new MassDEP regulations, setting graduated restrictions by drought level. This is a supply question rather than a quality one and it does not change what is in the water, but it is worth knowing before planning anything that uses water outdoors — and reverse osmosis systems send water to drain, which is a fair thing to raise in a drought year.

The City of Cambridge Annual Drinking Water Quality Report for public water system 3049000, whose masthead states Water Quality Information From 2025 and Distributed June 2026, plus the federal and Massachusetts drinking water standards the report compares against. The lead and copper figures within it carry the report's own footnote dating them to 2023 and are presented that way here. The hardness figure is not in the report at all; it is derived from the reported calcium and magnesium using the standard conversion, and is shown as a derivation rather than quoted as a result. Independent compilations of water quality data exist and are not the source used on this page. Every figure is a system-level or sampling-round result, and none of it is a reading at your address.