Gillette water is extremely hard at 18.4 to 29 grains per gallon across two blending zones, and Powder River Basin mines send fine dark coal and haul-road dust.
Gillette's water is extremely hard, 18.4 to 29 grains per gallon depending on which side of the Wyodak blending point a house sits, so tap water left on glass dries to a heavy white crust. The coal is on the glass too: fine dark dust off the Powder River Basin mines and haul roads clings, and it needs detergent and a real rinse rather than a wipe. August and September are the reliable months, interval sets the price, and a single-story exterior runs $180 to $320.
Not sourced, and held at that rather than upgraded to not published. The city's 2025 report puts hardness at 18.4 to 29 grains per gallon, about 315 to 496 mg/L, which is very hard on the USGS scale. What the federal record does say is suggestive without being conclusive: the treatment train is packed-tower aeration and hypochlorination, which strips dissolved gas and does nothing to mineral, so whatever the aquifer delivers arrives essentially unaltered. Judge a test pane rather than a number.
Figures by zone, as reported.
| Hardness | 315–496 mg/L as CaCO₃ Printed in grains per gallon: 27.5 to 29 east of the Wyodak blending point and 18.4 to 24.6 west of it, about 315 to 496 mg/L; very hard on the USGS ladder, as published by the City of Gillette. |
|---|---|
| pH | 7.4–7.8 |
| Alkalinity | 213–264 mg/L as CaCO₃ |
| Iron | not detected |
| Sodium | 4–56 mg/L |
| Total dissolved solids | 521–624 mg/L |
| Disinfectant | free chlorine |
| Source and treatment | Groundwater, per the EPA SDWIS federal record · Packed-tower aeration with pre and post chlorination; SDWIS records no filtration for the system · No softening step. |
Not in the report: corrosion index, manganese and chloride.
SOURCE · City of Gillette Water Division, 2025 Consumer Confidence Report, with the EPA SDWIS federal treatment record · How we source these numbers
The mines do not have a season and neither does their dust, which is why mine-adjacent and industrial-corridor frontage runs on a fixed interval here rather than a seasonal one. What is seasonal is everything else: blown prairie dust through the dry spring and summer, fast afternoon dry-down through high summer, and a hard close once overnight freezes arrive. The residential wash that holds is a late-summer one, and it will still not hold as long on the western elevations as on the eastern.
WYOMING SEASON BY SEASON →Gillette is a coal city and the coal is on the glass. The Powder River Basin surface mines around it are the largest in the country, and the fine dark dust off haul roads and stockpiles is a genuinely distinctive deposit — it clings, it needs detergent and a real rinse rather than a wipe-over, and on mine-adjacent elevations it sets a shorter interval than anything the weather would justify. The water is extremely hard: the City publishes 18.4 to 29 grains per gallon across its two blending zones, and the federally recorded treatment is packed-tower aeration, which strips gas rather than removing mineral. Above ground the constraints are High Plains constraints: persistent wind, fast summer dry-down, and a hard close to the exterior season. The housing stock is unusually uniform for a city this size because it arrived in boom-sized tranches, which makes reach the pricing question and coating damage the risk.
The City of Gillette publishes hardness in grains per gallon for each side of the Wyodak blending point: 27.5 to 29 east and 18.4 to 24.6 west, roughly 315 to 496 milligrams per litre. The two zones differ enough that the side of town a house sits on decides how much pure-water rinsing a job needs.
"Gillette-Madison Water" is not the name of a utility, and it circulates as though it were. The operator of record is the City of Gillette; the Madison is the aquifer at the far end of a long-haul pipeline from the Black Hills flank, and the Gillette Madison Pipeline is the project that brings it in. Treating a pipeline project's name as the water company's is the kind of error that makes a page look sourced when it is not.
The federally recorded treatment train is aeration through a packed tower followed by hypochlorination. A packed tower strips dissolved gas out of groundwater rather than removing mineral — it is what a deep aquifer supply gets when the problem is gas rather than hardness, and it means nothing in the train is softening the water.
The city is also recorded federally as a wholesaler, which means Gillette treats and sells water beyond its own boundary. For a cleaner that matters in one practical way: the water in a job outside the city limits may well be Gillette's water, so a supply assumption that stops at the city line is wrong.
Gillette is the centre of American thermal coal, and the industrial dust load is genuinely different from anywhere else in this state. The Powder River Basin mines immediately around the city are the largest surface coal operations in the country, and haul-road and stockpile dust is a real and unusual deposit on glass — dark, fine and clinging, and it does not rinse off the way prairie dust does.
Coal-bed methane and oil-service traffic keeps a heavy-vehicle fleet moving on the roads around town year-round. Frontage on the arterials carries a diesel and road-film load that comes back on a fixed interval, which is what makes the commercial book here steadier than the population would suggest.
At about 4,550 feet on the northern High Plains the climate is semi-arid with a genuine continental swing: hot dry summer afternoons that flash a pane dry, and winters cold enough that the exterior season closes hard. The wind is persistent and there is nothing upwind to break it.
Gillette grew fast and late, and its housing stock shows it — successive energy booms put in large tranches of subdivision housing rather than a slow accumulation of eras. That means coated sealed units across most of the residential market and comparatively little genuinely historic glazing, which simplifies the chemistry question and sharpens the reach one.
Gillette prices on interval rather than difficulty. The industrial and mine-adjacent work is frequency work and it is the steadiest money in the city, which is unusual for a population this size and it holds residential rates down. Add for travel on the country acreage outside the city limits, add for reach on the newer north-side gable elevations, and expect the shorter interval on prevailing-wind elevations to show up as a return visit rather than a higher price per visit.
The coal dust is the argument here and it is a technical one rather than a matter of height. It is fine and dark and it clings, so wiping a dry pane grinds it in and a single pass of plain water smears it — the job needs a detergent wash and a proper rinse, in that order, and most homeowners try the reverse. Beyond that the newer subdivision stock is straightforward apart from the coatings, where the common household cleaners are exactly the ones that cause permanent damage.
OPEN COST ESTIMATOR →2025 annual mean at the Dry Fork Site DF-4 monitor, Dry Fork Mine Site 4, 6.8 km north-east of the city (EPA site 56-005-0897).
2025 annual mean at the Gillette Slams site monitor, Gillette - 1000 West 8th, 2.2 km north-west of the city (EPA site 56-005-1002).
Largest air release: 50 Buttes, 3669 South HWY 50 (natural gas processing), inside the city limits, 5,152 lb in 2024.
No one may tap, open or connect to Gillette's water mains without the city's permission. The city code treats watering that runs across the ground into gutters, streets or storm drains as wasted water, fined from $100 upward per day, and when the mayor proclaims a shortage, city water can be limited to domestic and sanitary needs with police able to shut off violators.
Gillette City Code §§17-25, 17-30 and 17-41: tapping mains; water waste; proclamation limiting use (rev. 09-2025) · checked September 2026
Gillette's sewer rules let only storm water, surface drainage and unpolluted water into designated storm sewers, bar anyone from putting chemicals, oil, grease or industrial waste into them, and require the approving authority's consent before anyone uses a storm sewer at all; discharging banned substances is a misdemeanor with fines up to $750 a day.
Gillette City Code §17-22(c): prohibited discharges, storm sewers (rev. 09-2025) · checked September 2026
Gillette's rewritten zoning code sets up agricultural, residential, commercial and industrial districts but no historic district or design review, mentioning history only to exempt historical markers from sign rules. The city's Historic Preservation Commission, formed in 2015, keeps local and National Register listings, so downtown window glass needs only ordinary permits.
Gillette Zoning Ordinance: establishment of zoning districts · City of Gillette: Gillette Historic Preservation Commission · checked September 2026
Gillette is the largest coal-producing county in the country (Campbell County). Coal-and-energy-services industrial residue on commercial glass facility-adjacent — coal-dust residue plus mineral residue composite plus drilling-mud-and-fines residue composite on the worst-affected stock. Extended alkaline-soap dwell plus citric-rinse handling. Same handling pattern Jan Davenport documents for North Dakota Bakken corridor.
Gillette-Madison Water supply at a published 315–496 mg/L (extremely hard), the hardest municipal water in the Mountain West. Extended citric pre-treatment (4-6 minutes) plus citric-rinse finish required. Verify chemistry on individual properties.
Not sourced, and held at that rather than upgraded to not published. The city's 2025 report puts hardness at 18.4 to 29 grains per gallon, about 315 to 496 mg/L, which is very hard on the USGS scale.
Residential window cleaning in Gillette typically runs $6–10 per pane or $180–320 for a standard single-story exterior. Gillette prices on interval rather than difficulty. The industrial and mine-adjacent work is frequency work and it is the steadiest money in the city, which is unusual for a population this size and it holds residential rates down.
Gillette's drier, frost-free months are August and September, by NOAA's 1991–2020 normals for the Gillette Campbell Airport station, where May brings the most rain. The calendar on this page marks August (after the May 20 bloom and after smoke season). Frost nights usually run from September 25 to May 22.
Not as the final rinse: the City of Gillette publishes dissolved solids of 521–624 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. A deionising cartridge yields about 16% of what it would on 100 mg/L water. SDWIS records no filtration or softening for the system.
In Gillette the dominant residue patterns include very hard water, published at 18.4 to 29 grains per gallon across the city's two blending zones and fine dark coal and haul-road dust from the powder river basin surface mines.
The coal dust is the argument here and it is a technical one rather than a matter of height. It is fine and dark and it clings, so wiping a dry pane grinds it in and a single pass of plain water smears it — the job needs a detergent wash and a proper rinse, in that order, and most homeowners try the reverse.
A compact commercial core, smaller and newer than the county's economy suggests. Street-level frontage with road film on a short interval; little of the heritage glazing that older Wyoming towns carry. South Gillette and the Boxelder area and North Gillette have their own housing stock and glazing as well.
Just over the Wyoming line