Portsmouth hardness ranges from 13 to 204 mg/L by source, estuary salt aerosol reaches well inland from the river, and winter road salt piles on top.
Portsmouth blends well water with the Bellamy Reservoir, so hardness runs from 13 to 204 mg/L depending on the source, soft on average but very hard at the top of the range, which makes a filtered final rinse cheap insurance. Salt from the estuary reaches well inland and winter road salt piles on top. In the historic core, small panes in quantity and original sash leave no room for speed, while a single-story exterior elsewhere runs $290 to $470 through a July to September season.
The city's 2025 report gives hardness as 44 mg/L on average, across a range of 13 to 204 — soft on average, very hard at the extreme. What the treatment train does suggest is a surface supply carrying organic colour and low-density solids rather than heavy mineral — dissolved air flotation is chosen for exactly that problem — with groundwater blended alongside it. For working purposes the mineral question is secondary here anyway: salt is the residue that governs this city, and it behaves nothing like scale.
| Hardness | 13–204 mg/L as CaCO₃ Soft on average, though the top of the range is very hard, as published by City of Portsmouth Department of Public Works, Water Division. |
|---|---|
| pH | 7.5 (range 6.3–8) |
| Alkalinity | 43 mg/L as CaCO₃ (range 7–175) |
| Iron | 0.015 mg/L (range 0–0.47) |
| Manganese | 0.014 mg/L (range 0–0.172) |
| Sodium | 44 mg/L (range 22–178) |
| Chloride | 73 mg/L (range 33–325) |
| Disinfectant | free chlorine |
| Source and treatment | Surface water, per the EPA SDWIS federal record · Powdered activated carbon, coagulation, rapid mix, flocculation, sedimentation and rapid sand filtration, pre and post chlorination, fluoridation, with orthophosphate and polyphosphate inhibitors and post pH adjustment · No softening step. |
Not in the report: corrosion index and total dissolved solids.
SOURCE · City of Portsmouth Water Division Annual Water Quality Report, Reporting Year 2025, Portsmouth Water System (PWS 1951010), water quality parameters table · How we source these numbers
Two salt sources run on opposite halves of the year and overlap in the middle. Marine aerosol is heaviest through autumn and winter storms, road salt from December to March, and the pair of them make the first spring service the heaviest of the year by a wide margin. Historic-core commercial runs on the tourist calendar instead: finished before opening from May through October, and far more relaxed in the off-season. The freeze line closes reliable exterior work for several months whatever the salt is doing.
NEW HAMPSHIRE SEASON BY SEASON →Portsmouth operates its own water system, blending groundwater with surface water from the Bellamy Reservoir in Madbury and Dover — impounded in 1960 expressly to supply the city and the air base at Pease — and treating it with coagulation, dissolved air flotation and dual media filtration before chlorination. The city's 2025 report puts hardness at 44 mg/L on average — soft — across a 13 to 204 range, which is what blending a reservoir with groundwater can do. The work is shaped by two things the water report cannot show: an estuary that puts salt on glass well inland, and a colonial building stock whose early glass and original putty rule out anything aggressive.
The city runs its own water system rather than buying from a regional supplier, drawing on a combination of surface water and groundwater.
The surface source is the Bellamy Reservoir, which sits in Madbury and Dover several miles inland, with water flowing from there to the treatment facility in Madbury.
Treatment is more involved than a simple filtration plant: coagulation, dissolved air flotation and dual media filtration, with sodium hypochlorite added for disinfection before the water enters distribution. Dissolved air flotation is a comparatively unusual step and is chosen for water carrying organic colour and low-density solids.
The reservoir dam was built in 1960 specifically to supply Portsmouth and the air base at Pease, which is why a small coastal city ended up with an impoundment in two other towns.
Salt air is the defining exposure and the estuary makes it worse than a straightforward ocean frontage would. The Piscataqua runs hard with the tide, and the resulting aerosol reaches glass well back from the water rather than only on the first row.
Winter compounds it. Road salt on the streets and marine salt off the river arrive on the same glass, and both are hygroscopic — they pull moisture back and stay active rather than drying to something that brushes off.
The colonial building stock is the other defining fact and it is not a marketing line here. Early glass is thin, uneven and irreplaceable, set in putty that is often original, and it will not tolerate pressure, scraping or aggressive chemistry.
Small panes in large numbers make pane count the unit of work through the whole historic core. A modest-looking sash in Market Square can carry twenty individual lights, each with four edges and a putty line.
The tourist season inverts commercial scheduling. From late spring the downtown frontages must be finished before trade begins, which pushes the commercial book into early mornings and compresses the working day.
Pease is the counterweight in the market: modern, uniform, accessible glazing with professional facilities management, and the one place in the city where volume work at a predictable rate is available.
Pane count and care level set the historic-core price, and both run high — small lights in quantity, original material, and no scope for speed. Exposure sets the interval on anything facing the river, which raises annual value on the waterfront properties. Pease prices on volume and predictability at the other end of the scale. Across all of it the season is short, so the eight workable months carry the year and the schedule is priced accordingly.
Modern glass on the west side and at Pease is ordinary homeowner work. The historic core genuinely is not, and the reason is the glass rather than the height — early panes are thin and uneven, original putty crumbles under pressure, and a scraper that would be routine on float glass will take the surface off something irreplaceable. Salt wants flooding and rinsing rather than scrubbing. Anyone unsure which era a sash belongs to should treat it as the older one.
OPEN COST ESTIMATOR →2025 annual mean at the Portsmouth - Peirce Island monitor, Portsmouth, Peirce Island, 3.1 km north-east of the city (EPA site 33-015-0014).
Largest air release: Essential Power Newington, 200 Shattuck WAY (electric utilities), 0.7 km outside the city limits, 12,091 lb in 2024.
Portsmouth's water utility rules say hydrants, public or private, may be used only to fight fires or for purposes the Utility authorizes, and only the Utility or its agents may operate one. For any other use the Utility must give written permission and fit its own adapter, and the user pays a cash deposit and the water charge.
Portsmouth Ordinances Chapter 16, Section 16.115: hydrants · checked September 2026
Portsmouth's storm water ordinance bans every discharge to the storm drainage system that isn't on its allowed list. Residual street wash water is allowed only when detergents aren't used, and individual residential car washing is the only washing named, so detergent rinse from a commercial job is a prohibited discharge.
Portsmouth Ordinances Chapter 16, Sections 16.204 and 16.205: allowed and prohibited discharges · checked September 2026
Portsmouth's Historic District Commission issues Certificates of Approval, which are required for certain exterior changes to buildings and structures inside the city's Historic District; the commission meets monthly at City Hall and publishes its Rules & Procedures. Window replacement on a downtown building should be checked with the commission before work begins.
City of Portsmouth, Planning: Historic District Commission · checked September 2026
Late-winter and early-spring ice-melt residue carries chloride-residue, mineral residue, and organic residue composite. Ice-dam meltwater residue from roof-edge ice damming produces a distinctive composite residue on upper-pane and sash-perimeter glass. Percarbonate-citric ladder protocol required on the worst-affected stock.
The city's 2025 report gives hardness as 44 mg/L on average, across a range of 13 to 204 — soft on average, very hard at the extreme. What the treatment train does suggest is a surface supply carrying organic colour and low-density solids rather than heavy mineral — dissolved air flotation is chosen for exactly that problem — with groundwater blended alongside it.
Residential window cleaning in Portsmouth typically runs $10–15 per pane or $290–470 for a standard single-story exterior. Pane count and care level set the historic-core price, and both run high — small lights in quantity, original material, and no scope for speed.
Portsmouth's drier, frost-free months are July to September, by NOAA's 1991–2020 normals for a station near Durham, where June brings the most rain. The calendar on this page marks July (after the May 14 bloom and after smoke season). Frost nights usually run from October 4 to May 7.
Not as the final rinse: City of Portsmouth Department of Public Works, Water Division publishes hardness of 13–204 mg/L, enough to spot as it dries, so finish with pure water. Water left to dry leaves mineral scale; fresh spots lift with a mild acid. Treatment starts with powdered activated carbon, coagulation, rapid mix and flocculation.
In Portsmouth the dominant residue patterns include estuarine salt aerosol reaching well inland from the river and winter road salt compounding the marine load. Two salt sources run on opposite halves of the year and overlap in the middle.
Modern glass on the west side and at Pease is ordinary homeowner work. The historic core genuinely is not, and the reason is the glass rather than the height — early panes are thin and uneven, original putty crumbles under pressure, and a scraper that would be routine on float glass will take the surface off something irreplaceable.
Dense brick commercial around the square, much of it 18th and 19th century with small-paned upper sash above modern shopfronts. Two eras on one facade and two methods with them. Strawbery Banke and the South End and The waterfront and Piscataqua frontage have their own housing stock and glazing as well.
Just over the New Hampshire line