Cambridge water carries 180 mg/L chloride and 106 mg/L sodium, which the department puts down to road salt, with dissolved solids at 380 mg/L.
Cambridge publishes calcium and magnesium but no total hardness, so no figure is given here, but its water carries high chloride and sodium from road salt, which leaves a film that holds moisture on the glass. Heavy winter snow brings more road salt, so July to October is the reliable window. Tight lots make access the hidden cost, and a single-story exterior runs $380 to $620.
No hardness value is claimed for Cambridge because the department publishes calcium and magnesium separately but never a total, and converting the two into a figure the operator declined to state would be inventing a measurement rather than reporting one. What can be said with confidence is that the dissolved load is dominated by road salt rather than by carbonate: at 180 mg/L chloride and 106 sodium, the residue that matters here is salt-like and damp rather than chalky and dry, and it wants flooding off rather than polishing away.
| Hardness | not published Cambridge Water Department publishes no hardness figure in its Drinking Water Quality Report (PWS ID 3049000). |
|---|---|
| Sodium | 106 mg/L |
| Chloride | 180 mg/L |
| Total dissolved solids | 380 mg/L |
| Disinfectant | ozone + chloramine |
| Source and treatment | Surface water, per the EPA SDWIS federal record · Coagulation, rapid mix, flocculation, dissolved air flotation and rapid sand filtration, pre and post ozonation, chlorination with chloramines as the residual, fluoridation and pH adjustment for corrosion control · No softening step. |
Not in the report: pH, alkalinity, corrosion index, iron and manganese.
SOURCE · Cambridge Water Department 2025 Annual Drinking Water Quality Report, PWS ID 3049000, Secondary/Guidance Compounds table, with the EPA SDWIS federal treatment record · How we source these numbers
Salt runs the calendar from both directions. It arrives on the glass from the street through the whole treated season, and it is in the supply itself at levels the department attributes to the same source. Spring lifts the accumulated winter load in one heavy clean. Summer is the productive window, with the important caveat that in a declared drought year the outdoor water needed to do the work may be restricted or prohibited outright, which is a scheduling risk unique to this part of this site.
MASSACHUSETTS SEASON BY SEASON →Cambridge runs its own water rather than taking the regional supply, drawing on Hobbs Brook, Stony Brook and Fresh Pond and treating at the Walter J. Sullivan facility through ozone, dissolved air flotation, granular activated carbon and a monochloramine residual. Its report does not publish a total hardness figure — it gives calcium at 22 mg/L and magnesium at 4.6 but no total — so none is asserted here. What the report does publish matters more anyway: chloride at 180 mg/L and sodium at 106, both attributed by the department to road salting, with dissolved solids at 380. A large share of what a drying droplet leaves on Cambridge glass is therefore chloride rather than scale, and chloride is hygroscopic, so it behaves like coastal salt film rather than lime. There is also a constraint peculiar to this city: from 2025 customers must follow state drought-map outdoor water-use restrictions, which at higher levels ban non-essential outdoor use altogether.
Cambridge does not drink its neighbour's water despite being surrounded by the regional system. It runs its own reservoirs — Hobbs Brook Upper and Lower, Stony Brook, and Fresh Pond as the terminal reservoir — with watersheds reaching into Waltham, Lexington, Lincoln and Weston, and treats the water itself at the Walter J. Sullivan facility at Fresh Pond. The regional system exists only as a backup interconnection.
No hardness figure is stated here because the department's own report does not publish one. Read through, the 2023 report gives calcium at 22 mg/L and magnesium at 4.6 in its secondary and guidance table, but it prints no total hardness row, and deriving one from the constituents would be manufacturing a number the operator never stated.
What the report does publish is more startling for anyone cleaning glass: chloride at 180 mg/L and sodium at 106, both attributed by the department to road salting, against total dissolved solids of 380. That is a large dissolved load and a great deal of it is salt.
Those figures change what an evaporating droplet leaves behind. In most cities the residue from tap water is mineral scale; here a significant fraction of it is chloride, which is hygroscopic and behaves on glass more like coastal salt film than like lime. It stays damp and it keeps attracting what is in the air.
The treatment train is unusually elaborate for a city this size and it is worth knowing what is in the water as a result: preoxidation with ozone, coagulation and dissolved air flotation, a second ozone stage, granular activated carbon filtration, chlorine followed by monochloramine for the residual, then pH adjustment and fluoride.
The carbon stage carries real weight. The department replaced its filter media specifically to remove PFAS, began monitoring more than a year before the state set standards, and reports that results have been non-detect since — a level of pre-emption most utilities did not attempt.
There is also a constraint here that affects the trade directly and almost nowhere else on this site does. Cambridge sits in the state's Northeast drought region, and from April 2025 customers are required rather than asked to follow regional outdoor water-use restrictions tied to the state drought map — restrictions that at the higher levels ban non-essential outdoor water use outright.
Lot density is the quiet cost driver, because a crew that cannot position equipment spends its time solving access rather than cleaning glass. The laboratory and institutional market is large, well funded and contracted, which sets a high floor for commercial rates. Drought restrictions introduce a genuine planning risk into summer scheduling that crews elsewhere on this site do not have to price for.
Triple-decker Cambridgeport is the awkward middle case: three storeys of ordinary glazing on lots too tight to stand a ladder safely, which pushes a lot of otherwise routine work toward professionals. Institutional frontage around the colleges and the laboratory curtain wall in the eastern districts are contracted markets with access rules attached. Ground-floor and two-storey work in the northern neighbourhoods is straightforward, provided salted glass is flooded rather than wiped.
OPEN COST ESTIMATOR →2025 annual mean at the Dudley Square Roxbury monitor, Harrison AVE, 6 km south-east of the city (EPA site 25-025-0042).
2025 annual mean at the Boston Kenmore SQ monitor, Kenmore SQ, 3.5 km south-east of the city (EPA site 25-025-0002).
Largest air release: Matep LLC, 474 Brookline AVE (electric utilities), 1.7 km outside the city limits, 7,975 lb in 2024.
A Cambridge owner or occupant who leaves service pipes and fixtures defective for more than three days, or who neglects to shut the water off after use so that it runs to waste, is liable to a fine.
Cambridge Municipal Code §13.08.100: pipe and fixture maintenance, unnecessary use · checked September 2026
Cambridge forbids sweeping the litter from any building or lot into a gutter, street or square, and its leaf-blower rules add that no litter or debris may be blown, swept or raked into catch basins, so squeegee grit and sill dirt have to be bagged rather than pushed to the kerb inlet.
Cambridge Municipal Code §8.24.040: keeping premises and adjacent areas free of litter · Cambridge Municipal Code §8.16.081.3: leaf blower use regulations · checked September 2026
No Cambridge landmark, and no structure in a neighborhood conservation district, may be built or altered in any way that affects exterior architectural features unless the Historical Commission or the district's own commission approves, apart from what the designating order allows.
Cambridge Municipal Code §2.78.210: certificates of appropriateness · checked September 2026
MassDOT and the municipal road commissions apply heavy salt loads to keep the state's narrow secondary roads passable through the winter. Salt aerosol on ground-floor glass within a quarter-mile of any plowed road is the dominant winter contamination pattern, and slush splatter from passing traffic coats the lower third of ground-floor glass on road-facing exposures. The post-winter call drives the entire residential spring schedule from the first week of April through the second week of May.
The New England triple-decker housing stock — Worcester, Lowell, Lawrence, Lynn, parts of Boston and Cambridge — concentrates rainwater runoff through cornice-and-gutter systems that frequently overwhelm during heavy rain. Resulting streaking patterns on the upper-floor glass require a citric pre-treatment and a longer dwell time than ordinary cleaning. The pattern is endemic to the substrate and most New England cleaners recognize it without needing it diagnosed.
No hardness value is claimed for Cambridge because the department publishes calcium and magnesium separately but never a total, and converting the two into a figure the operator declined to state would be inventing a measurement rather than reporting one.
Residential window cleaning in Cambridge typically runs $13–19 per pane or $380–620 for a standard single-story exterior. Lot density is the quiet cost driver, because a crew that cannot position equipment spends its time solving access rather than cleaning glass.
Cambridge's drier, frost-free months are July to October, by NOAA's 1991–2020 normals for the Boston Logan International Airport station, where December brings the most rain. The calendar on this page marks July (after the May 5 bloom) and October (after smoke season and before frost). Frost nights usually run from November 9 to April 4.
Not as the final rinse: Cambridge Water Department publishes dissolved solids of 380 mg/L, enough to spot as it dries, so finish with pure water. Its sodium, up to 106 mg/L, leaves a salt film that pulls moisture back, so rinse it off rather than let it dry. Treatment starts with coagulation, rapid mix, flocculation and dissolved air flotation.
In Cambridge the dominant residue patterns include no total hardness figure published by the operator — calcium 22 mg/l and magnesium 4.6 are given, the total is not and chloride at 180 mg/l and sodium at 106, both attributed by the department to road salting. Salt runs the calendar from both directions.
Triple-decker Cambridgeport is the awkward middle case: three storeys of ordinary glazing on lots too tight to stand a ladder safely, which pushes a lot of otherwise routine work toward professionals. Institutional frontage around the colleges and the laboratory curtain wall in the eastern districts are contracted markets with access rules attached.
Institutional buildings of every era from the eighteenth century onward alongside dense commercial frontage, much of it with period sash under university stewardship and fixed maintenance schedules. Kendall Square and Cambridgeport have their own housing stock and glazing as well.
Just over the Massachusetts line