Detroit's unsoftened Great Lakes supply averages 107 mg/L hard, and lead service line replacement stirs up main sediment on the affected streets.
Detroit's Great Lakes water is moderately hard on average and is not softened, so a rinse left to dry leaves light spots rather than etching the glass. Lead service line replacement can stir sediment into the water on affected streets, so rinse with care while crews are working nearby. June, August and October are the best months; long elevations with divided sash in the historic districts take longer, while a single-story exterior runs $300 to $510.
DWSD's 2025 tap-water mineral analysis gives hardness averaging 107 mg/L (96 to 142): moderately hard water. The supply is Great Lakes surface water that is not softened in treatment, which points toward deposit on evaporation rather than etching.
| Hardness | 96–142 mg/L as CaCO₃ 2025 tap-water mineral analysis: average 107 mg/L, range 96 to 142, on Detroit River water treated by GLWA; moderately hard on the USGS ladder, as published by Detroit Water and Sewerage Department, on treated water from the Great Lakes Water Authority. |
|---|---|
| pH | 7.2 (range 6.96–7.92) |
| Alkalinity | 71 mg/L as CaCO₃ (range 60–78) |
| Iron | 0.2 mg/L (range 0–0.3) |
| Manganese | 0–0.002 mg/L |
| Sodium | 3.6 mg/L (range 0.4–9) |
| Chloride | 11 mg/L (range 8–16.4) |
| Total dissolved solids | 112 mg/L (range 15–158) |
| Disinfectant | ozone + chlorine |
| Source and treatment | Treated surface water from the Great Lakes Water Authority, distributed by Detroit · Powdered activated carbon, coagulation, flocculation, rapid mix, sedimentation and rapid sand filtration, post-ozonation and pre and post chlorination, fluoridation and an orthophosphate inhibitor · No softening step. |
Not in the report: corrosion index.
SOURCE · Detroit Water and Sewerage Department 2025 Water Quality Report, City of Detroit Tap Water Mineral Analysis, with the EPA SDWIS federal treatment record · How we source these numbers
Physical load dominates and it is geographic rather than seasonal: arterial frontage and river-facing industrial elevations reload within weeks, quiet residential streets within months. Organic load follows the regional calendar, tree pollen through spring and ragweed from August until frost. The one unpredictable input is main work — a street under service line replacement will dirty glass on a timetable set by the contractor, not the weather.
MICHIGAN SEASON BY SEASON →Detroit is a glazing-identification city before it is a water city. The supply is treated Great Lakes water, and DWSD's own 2025 mineral analysis puts its hardness at 96 to 142 mg/L, averaging 107. What actually governs the work is the age and unevenness of the building stock: original sash and art glass in Indian Village and Corktown sitting a few miles from coated insulated units on infill, so the first move at an unfamiliar address is always identification. Two local conditions sit on top of that. Lead service line replacement is active across the city, and a disturbed main puts sediment into the rinse water on the day it is worked. Arterial and river-frontage elevations carry a bonded combustion film that a water-fed rinse will not lift. Seasonally it is a compressed exterior year with a commercial book carrying the cold months.
The utility structure here is genuinely two organisations and it matters for anyone trying to check a figure. The Great Lakes Water Authority treats the water at plants drawing from Lake Huron and the Detroit River; the Detroit Water and Sewerage Department distributes it to addresses inside the city. GLWA was created in 2016 under the city's bankruptcy settlement, with DWSD retained as the retail provider within Detroit itself, so a question about treatment and a question about the pipe at the kerb go to different bodies.
DWSD's 2025 tap-water mineral analysis puts total hardness at an average of 107 mg/L, ranging from 96 to 142. That is worth stating plainly because figures quoted online for Detroit range from moderately hard to very hard. Any of them would look authoritative on a page. None of them is.
Lead service lines are the live water issue in this city rather than hardness, and a crew should know why that is not their problem and where it becomes one. Detroit carries tens of thousands of lead service lines and an active replacement programme, which means a street being worked is a street where the main has been disturbed. Disturbed mains put sediment into the line, and sediment in the rinse water is visible on glass immediately.
The housing stock is older than almost any comparable American city and the practical consequence is that assumptions do not travel between addresses. A block can hold a 1910 frame house with original sash next to a 1990s infill with coated insulated units, and the correct treatment for one will damage the other. In this city the identification step is not optional professionalism, it is the job.
Vacancy changes the work in a way that no chemistry does. Long-vacant neighbouring property means blown debris, unmaintained vegetation and in places broken glass at ground level, and a crew setting ladders on those streets is managing a site rather than just a wash. It also means the occupied addresses are worth more per visit, because they are holding a line rather than following a fashion.
Detroit is an automotive city and still an industrial one, and the airborne load reflects it. Elevations facing the major arterial corridors and the industrial river frontage carry a combustion and tyre-particulate film that residential side streets do not, and that deposit bonds rather than sitting loose — it needs a detergent wash, not a rinse.
The seasonal shape is a genuine constraint on the trade rather than a footnote. The city holds a real freeze through midwinter, which takes exterior residential work off the table for a stretch, and the commercial book is what carries crews through it. Freeze-thaw on the pre-war stock is the damage risk that follows, and it argues for washing with a dry-down window rather than merely on a mild afternoon.
Pane count drives the historic detached districts, where elevations are long and sash are divided. Site conditions drive the thinner neighbourhoods, where setting up safely takes longer than the wash. Frequency drives downtown and Midtown, where street-facing commercial glass justifies an interval contract and those contracts are what let a crew price residential work on the same route more keenly.
Post-war single-storey stock on the outer edges is reasonable homeowner work. Nothing in Indian Village, Boston-Edison or Corktown is, because the risk is not the height but the glass: art glass panels and original putty both punish standard household products and standard scrapers. Downtown high-rise work is a licensed and insured trade and should never be attempted from a ladder.
OPEN COST ESTIMATOR →2025 annual mean at the Detroit-Southwest monitor, 150 Waterman St (DET-SW), 8.9 km south of the city (EPA site 26-163-0015).
2025 annual mean at the Military Park (GHIB) monitor, 1238 Military ST (DET-Military Park), 7.9 km south of the city (EPA site 26-163-0100).
Largest air release: EES Coke Battery LLC, 1400 ZUG Island (petroleum), 0.1 km outside the city limits, 614,758 lb in 2024.
Detroit's code sets no everyday limits on outdoor water use. When demand on the system threatens public health and safety, the Board of Water Commissioners can ask City Council to pass an emergency ordinance, for a set period, that bans outdoor water use across the city or restricts it.
Detroit City Code §48-1-6: conservation of water during emergencies · checked September 2026
Detroit's sewer code sends stormwater and other unpolluted water to the combined or storm sewers, but bars anyone from putting chemicals, acids, oily wastes, sand and similar material into any public sewer, free or in solution, and from removing catch basin or inlet covers. Wash water carrying cleaning chemicals should not go down a catch basin.
Detroit City Code §48-2-9: use of public sewers · checked September 2026
Before any work starts in a Detroit historic district, interim and proposed districts included, a permit application must go to the Buildings, Safety Engineering and Environmental Department, and no work may begin until it is issued. The Historic District Commission judges the work against the district's elements of design and federal rehabilitation standards, issuing a certificate of appropriateness when it fits.
Detroit City Code §21-2-71: permit required for work in historic districts · Detroit City Code §21-2-78: determinations of the Historic District Commission · checked September 2026
MDOT is one of the heaviest salt-using transportation departments in the country. Salt aerosol from the roadways deposits on ground-floor glass within a quarter-mile of any plowed road and corrodes aluminum and steel sash hardware over time. Slush splatter from passing traffic coats the lower third of ground-floor glass on every house within thirty feet of a curb. The post-winter call is the entire residential spring season here.
Shoreline counties (Macomb, Ottawa, Berrien, Charlevoix) see ice-fog deposition during cold-water-warm-air events that crystallizes a thin frost layer on exterior glass and screens. Clears with above-freezing temperatures but the cumulative effect on screen mesh and gasket flexibility is meaningful over a decade.
DWSD's 2025 tap-water mineral analysis gives hardness averaging 107 mg/L (96 to 142): moderately hard water. The supply is Great Lakes surface water that is not softened in treatment, which points toward deposit on evaporation rather than etching.
Residential window cleaning in Detroit typically runs $10–15 per pane or $300–510 for a standard single-story exterior. Pane count drives the historic detached districts, where elevations are long and sash are divided.
Detroit's drier, frost-free months are June, August and October, by NOAA's 1991–2020 normals for the Detroit City Airport station, where May brings the most rain. The calendar on this page marks June (after the May 6 bloom) and October (after smoke season and before frost). Frost nights usually run from October 31 to April 21.
Yes, if the rinse is squeegeed off before it dries: Detroit Water and Sewerage Department, on treated water from the Great Lakes Water Authority publishes dissolved solids of 112 mg/L, between this site's two dissolved-solids flags. It draws on treated surface water from the Great Lakes Water Authority, distributed by Detroit.
In Detroit the dominant residue patterns include mineral deposit from an unsoftened great lakes supply averaging 107 mg/l of hardness and disturbed main sediment on streets undergoing lead service line replacement.
Post-war single-storey stock on the outer edges is reasonable homeowner work. Nothing in Indian Village, Boston-Edison or Corktown is, because the risk is not the height but the glass: art glass panels and original putty both punish standard household products and standard scrapers.
Large early twentieth-century houses on deep lots, with leaded and art glass common in stair, entry and dining positions. Those panels take a different chemistry from the float glass beside them, and identifying them before starting is the whole job on a first visit. Corktown and Boston-Edison and Palmer Woods have their own housing stock and glazing as well.
Just over the Michigan line