Portland's water is very soft at 7.2 mg/L. Marine aerosol off the harbor reaches well inland, and narrow streets throw winter road-salt spray.
Portland's Sebago Lake water is about as soft as tap water gets, 7.2 mg/L in the district's latest report, so there is essentially nothing in it to leave on glass. Salt is the issue instead: harbour air carries well inland, and narrow streets throw road-salt spray onto lower panes all winter. Crews sell their time inside a short season, July to September is the dependable stretch, and a single-story exterior runs $270 to $460.
At 8 to 9 milligrams per litre with calcium at 3.2 and magnesium under 1, this is about as close to no dissolved mineral as a municipal supply gets. The district says so itself and adds that softening is unnecessary. For a cleaner that means the supply rinses clean and leaves nothing, which is a genuine advantage — and it means a poor result in this city is a technique or a soiling problem rather than a water one, which is a useful thing to know before blaming the tap.
| Hardness | 7.2 mg/L as CaCO₃ Soft — the district reports 7.2 mg/L in its 2026 annual report and gives the Sebago Lake source a value of 9 on its customer FAQ, describing it as soft against its own 0 to 75 soft band, as published by Portland Water District. |
|---|---|
| Iron | 0.014 mg/L |
| Manganese | 0.0014 mg/L |
| Sodium | 9.5 mg/L |
| Chloride | 11 mg/L |
| Disinfectant | chloramine |
| Source and treatment | Sebago Lake, drawn through two large screened intake pipes. The lake is 316 feet at its deepest with a five-year residence time, which is why the mineral figures move by about one milligram between editions rather than swinging with conditions. · A multi-barrier disinfection process: ozone gas bubbled through the water first, then ultraviolet light to inactivate remaining pathogens, then a small monochloramine dose for the distribution residual. pH is adjusted with sodium hydroxide, zinc orthophosphate is dosed for corrosion control and has been optimised since 2002, and fluoride is added. · No softening step. |
Not in the report: pH, alkalinity, corrosion index and total dissolved solids.
SOURCE · Portland Water District, 2026 Annual Water Quality Report, 'Mineral Content and Secondary Standards' table and the treatment-process and corrosion-control sections (pwd.org). Portland is PWD's home system. · How we source these numbers
Salt runs the year from both ends. Marine aerosol is heaviest through autumn and winter storms and never fully stops; road salt runs December to March; and the two together make the first spring service by far the heaviest of the year. Inside the short season the work holds well because the water leaves nothing behind. The freeze line is the hard constraint, closing reliable exterior work for months and compressing the year into roughly seven.
MAINE SEASON BY SEASON →Portland's district publishes hardness openly — 7.2 mg/L in its 2026 report, 9 on its customer FAQ — with calcium 3.2 and magnesium below 1 alongside it. Sebago Lake is deep, cold and oligotrophic with a residence time over five years, and the figure moves by about a milligram between years rather than swinging. There is essentially nothing here to deposit. Salt is what defines the work instead — marine aerosol off a working harbour and months of road treatment, both hygroscopic.
Portland's water is among the softest municipal supplies in the country, and the district publishes the figure without being asked: its 2026 report gives hardness at 7.2 milligrams per litre, and its customer FAQ gives the Sebago Lake source a hardness value of 9.
The district publishes the constituents alongside it, which is rarer and more useful — calcium at 3.2 milligrams per litre and magnesium below 1.
At those levels there is essentially nothing in this water to deposit. Mineral spotting is not a Portland problem and no product sold to fight it will earn its keep here.
The 2026 report's secondary figures reinforce the picture: chloride 11, sodium 9.5, iron 0.014 and manganese 0.0014. This is a very lightly mineralised supply by any standard.
Year-to-year stability is worth noting too. An earlier report gives hardness 7.0 with calcium 2.8, so the figure moves by about a milligram across years rather than swinging with conditions — unusual on this site.
The source explains it. Sebago Lake is deep, cold and oligotrophic — 316 feet at its deepest, Maine's second largest — with a residence time of five years or more, and it has supplied the city since 1869.
The district also states its own position plainly: a value below 100 milligrams per litre is ideal for ordinary domestic purposes, so softening is unnecessary for residential customers.
What replaces minerals here is salt, from two directions. The city sits on a peninsula in a working harbour, so marine aerosol reaches glass well back from the water.
Road salt does the rest. Maine winters put treatment on the streets for months, and on narrow peninsula streets the spray reaches everything below the second storey.
Both are hygroscopic, so they re-wet rather than drying to something that brushes off — which is why salt rather than scale is the residue that defines this market.
The building stock is exceptionally old and dense for a city this size, with whole districts of pre-1900 fabric, and much of it carries original glass that a confident scraper will destroy.
The season is short and hard-edged. Freeze-thaw closes reliable exterior work for months, so the year's revenue is carried in roughly seven months and the spring reopening is always the heaviest service.
Season is the dominant economic fact, with roughly seven usable months carrying the year, so capacity inside them is what is really being sold. Pane count and original fabric price the West End and Munjoy Hill well above their glass area. The Old Port prices on constrained access and finishing before trade. Exposure raises frequency on anything facing the harbour. Water treatment contributes nothing at all.
The water could hardly be more cooperative, so a homeowner gets a good result on accessible glass. Salt is the thing that wants technique rather than product — flood and rinse rather than mixing stronger, because concentration leaves more to re-dissolve. The real limits are structural: Munjoy Hill and the West End have narrow streets, steep ground and pre-1900 sash with original putty, and the working waterfront has access and scheduling constraints that are not domestic problems.
OPEN COST ESTIMATOR →2024 annual mean at the TB - Tukey's Bridge monitor, TUKEY'S Bridge-Bean POT RD., 2.9 km east of the city (EPA site 23-005-0015).
Largest air release: Sappi N.A. - Westbrook Operations, 89 Cumberland ST (paper), 1.4 km outside the city limits, 78,175 lb in 2024.
Portland's water supplier, the Portland Water District, charges customers who ignore mandatory conservation or use restrictions during a declared supply emergency a fee of twice the reconnection charge for every 24 hours out of compliance, and can shut off repeat violators; its filed terms also bar anyone but district staff from opening a hydrant.
Portland Water District Terms and Conditions §170: water supply emergency · Portland Water District Terms and Conditions §140: tampering with district property · checked September 2026
Portland's storm water chapter, revised in June 2024, forbids anyone to create or maintain a non-storm water discharge to the storm drainage system unless it is on the allowed list. That list covers lawn watering, hydrant flushing, home car washing and leftover street wash water only when no detergent is used; commercial building washing is not on it.
Portland City Code Ch. 32 Sec. 32-18: prohibition of illicit connections and discharges (rev. 6-17-24) · checked September 2026
Portland's Land Use Code requires a certificate of appropriateness from the Historic Preservation Board or planning staff before exterior alterations to landmarks and buildings in historic districts. Ordinary maintenance is exempt, and the code defines it to include replacing windows with ones of the same scale, texture and color, so matching glass swaps need no certificate.
City of Portland Land Use Code Article 17: Historic Preservation (amended 3/7/22) · 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.
Portland runs on Portland Water District lake or reservoir surface water at a published 7.2 mg/L (CaCO₃) — soft — the district reports 7.2 mg/L in its 2026 annual report and gives the Sebago Lake source a value of 9 on its customer FAQ, describing it as soft against its own 0 to 75 soft band.
Residential window cleaning in Portland typically runs $9–15 per pane or $270–460 for a standard single-story exterior. Season is the dominant economic fact, with roughly seven usable months carrying the year, so capacity inside them is what is really being sold.
Portland's drier, frost-free months are July to September, by NOAA's 1991–2020 normals for the Portland International Jetport station, where December brings the most rain. The calendar on this page marks July (after the May 18 bloom and after smoke season). Frost nights usually run from October 15 to April 26.
Usually yes: Portland Water District publishes hardness of 7.2 mg/L, low enough that tap-rinsed glass tends to dry clean. Iron, manganese, sodium and chloride all sit under this site's flags (highest: sodium up to 9.5 mg/L). It draws on Sebago Lake, drawn through two large screened intake pipes.
In Portland the dominant residue patterns include marine aerosol off the harbour reaching well inland and winter road salt and street spray on narrow streets. Salt runs the year from both ends.
The water could hardly be more cooperative, so a homeowner gets a good result on accessible glass. Salt is the thing that wants technique rather than product — flood and rinse rather than mixing stronger, because concentration leaves more to re-dissolve.
The 19th-century brick warehouse and commercial quarter on the working waterfront, with original storefront glazing above cobbled streets. Access is constrained, trade is heavy and frontages are judged closely. West End and Munjoy Hill have their own housing stock and glazing as well.
Just over the Maine line