Window Washing in Denver
Denver water runs 34 to 120 mg/L hard, but at mile-high altitude and low humidity it flashes dry on sunlit glass before a squeegee reaches it.
Denver's tap water is soft to moderately hard depending on which plant feeds the address, so mineral spots are a small problem next to the thin, dry air, which dries rinse water before a squeegee reaches it. Work shaded sides first and plan exterior washes for July to September, with hail cleanup a regular part of the year. A single-story exterior runs $300 to $550, and one severe storm can turn the whole metro into restoration work.
What the water means for the glass
There is no single Denver figure and the utility does not pretend otherwise: South Platte water runs 4 to 7 grains per gallon and Moffat water 2 to 4, so an address can be on water roughly twice as hard as its neighbour's depending on which plant feeds it. Both ends are mild by national standards. What actually governs the work here is the altitude and the dry air — rinse water flashes off a sunlit pane far faster than at sea level, so even this modest mineral load will mark glass if the blade does not keep up with the evaporation.
Denver tap water, by the numbers
Figures by plant, as reported.
| Hardness | 34–120 mg/L as CaCO₃ Published per source — the utility calls South Platte moderately hard to hard and Moffat softer; the combined span runs from soft into the top of moderately hard. |
|---|---|
| Alkalinity | 42–84 mg/L as CaCO₃ |
| Manganese | 0.0019 mg/L (range 0–0.0257) |
| Sodium | 12.3–23.82 mg/L |
| Chloride | 5–35 mg/L |
| Total dissolved solids | 91–225 mg/L |
| Disinfectant | chloramine |
| Source and treatment | Two source systems of mountain snowmelt and reservoirs — the harder South Platte and the softer Moffat — treated at the Marston, Foothills and Moffat plants, 715 MGD combined · Powdered activated carbon, permanganate, coagulation, flocculation, rapid mix, sedimentation, rapid sand filtration and sludge treatment, with chlorination, chloramines as the residual, ultraviolet radiation at part of the system, fluoridation, and phosphate inhibitor plus pH adjustment for corrosion control · No softening step. |
Not in the report: pH, corrosion index and iron.
SOURCE · Denver Water 2026 Water Quality Report (2025 data; copy posted by a distributor served with Denver Water supply) and Denver Water's brewing-water plant-effluent figures, with the EPA SDWIS federal treatment record, PWS CO0116001 · How we source these numbers
When a wash holds
What sets the cleaning clock
Altitude and dryness set the pace rather than mineral load. At a mile up with very low humidity, rinse water flashes off fast enough that the drying moment, not the dirt, decides the result — and that is true in February as much as July. The other clock is mechanical: spring snow is heavy and wet, and the road treatment that follows puts salt and traction sand onto lower glass through a long shoulder season.
COLORADO SEASON BY SEASON →What's specific to Denver
Denver Water runs snowmelt through several plants serving different parts of the metro and publishes hardness by source, from about 34 to 120 mg/L, so figures quoted online that give one number, or credit groundwater the utility does not use, are wrong. Operationally the altitude decides the method: at a mile up in dry air, rinse water flashes off before a squeegee finishes a large pane, in winter as much as summer. Hail is a recurring rather than exceptional part of the year.
Denver Water runs Rocky Mountain snowmelt through several treatment plants — Foothills, Marston and Moffat — serving different parts of the metro, and its own summary puts treated-water hardness between about 34 and 120 mg/L depending on the source. Multi-plant systems like this one usually publish per plant, so a citywide average may not exist.
Denver Water publishes the figure by SOURCE rather than as one city number, and prints it in both units for customers setting appliances. The South Platte supply it calls moderately hard to hard, varying seasonally between 4 and 7 grains per gallon and at times passing 100 mg/L; the Moffat supply is softer, swinging between 2 and 4 grains. Which of those reaches a tap depends on the plant serving it, and the utility publishes monthly plant-by-plant hardness alongside the narrative.
Figures quoted online for Denver disagree with each other, and some credit deep groundwater beneath the Front Range, a source Denver Water does not meaningfully draw. When a page is wrong about where the water comes from, its number is worth nothing, and every one of those figures sits above the top of the operator's own published band.
At a mile above sea level with very low humidity, rinse water flashes off far faster than at sea level, and that is as true in winter as in summer. The drying moment rather than the dirt decides the result on any sunlit elevation, which makes working order — shade first, sun last — the single most important habit here.
The Front Range hail corridor is among the most active in the country, and a severe storm reprices the whole metro in an afternoon. The correct first pass afterwards is low-pressure flooding, because the grit driven into screens and frame channels will score glass if it is dragged rather than floated.
Spring snow here is heavy and wet rather than powdery, and the road treatment that follows runs through a long shoulder season. Traction sand as much as salt ends up on lower glass, and sand is abrasive in a way that salt alone is not.
How old the glass is
- Before 1940 · 17%wood sash and older glass
- 1940–1959 · 17%steel casements, early aluminium
- 1960–1979 · 21%aluminium sliders, often single-pane
- 1980–1999 · 14%double-pane units become standard
- 2000–2009 · 11%vinyl frames, low-E spreading
- 2010 or later · 20%low-E common: gentle cleaners only
The city, by neighborhood
What window cleaning costs in Denver
Hail is the market's recurring disruptor and it should be priced as a feature of the year rather than a surprise. A single severe storm converts routes across the metro into restoration work simultaneously. Beyond that, the post-2010 downtown and RiNo development wave added curtain wall that is rope-and-stage work, and the foothills communities on the western edge combine steep access with large view-facing glass.
Doing it yourself
Working in high-altitude sun is the difficulty. On a large south or west pane the top dries before the bottom is finished, so a homeowner should work shaded elevations early and accept that the sunny side needs either shade, speed or someone with a pure-water system. The other local hazard is hail: Denver sits in one of the most hail-prone corridors in the country, and post-storm glass carries grit that must be floated off rather than dragged.
OPEN COST ESTIMATOR →2025 annual mean at the Birch Street monitor, 7275 Birch St, 8.8 km north-west of the city (EPA site 08-001-0010).
2025 annual mean at the Denver - NJH-E monitor, 14TH AVE. & Albion ST., 5.7 km south-west of the city (EPA site 08-031-0013).
Largest air release: Suncor Energy Commerce City Refinery, 5801 Brighton Blvd (petroleum), 0.8 km outside the city limits, 86,805 lb in 2024.
Denver Water has declared a Stage 1 drought: lawns may be watered only on two assigned days a week, before 10 a.m. or after 6 p.m., water must stay off pavement, sidewalks and streets, and a hose used for hand-watering or washing needs a shut-off nozzle. Commercial power washers have no day limits but must clean without water first, use high-efficiency equipment and prevent waste.
Denver Water, rules for outdoor water use (Stage 1 drought) · checked September 2026
Denver's code makes it unlawful to discharge polluted water into any storm sewer or watercourse in the city. The city's stormwater program warns that anything besides rain and snowmelt going down a storm drain can be a pollutant, and those drains carry it to waterways untreated, so keep soapy or dirty rinse water out of the gutter.
Denver Revised Municipal Code §56-102(a): polluted water prohibited in storm sewers · City and County of Denver, common stormwater pollutants · checked September 2026
Denver's Landmark Preservation staff and commissions review the design of every exterior project that needs a building or zoning permit on an individual landmark or on any property in a historic district, and window and door replacement is on the city's list of projects that go through that review. Lower Downtown has its own design review commission.
City and County of Denver, Landmark Preservation design review process · checked September 2026
What actually shows up on Denver glass
Dryland farming east of the Front Range generates serious dust events two or three times a year. Silt-and-clay fraction particulate, abrasive enough to scratch glass if dry-wiped. Pre-rinse heavily, never towel dry.
Denver, answered
How hard is the water in Denver, Colorado?＋
Denver runs on Denver Water lake or reservoir surface water at a published 34–120 mg/L (CaCO₃) — published per source — the utility calls South Platte moderately hard to hard and Moffat softer; the combined span runs from soft into the top of moderately hard.
How much does window cleaning cost in Denver?＋
Residential window cleaning in Denver typically runs $10–16 per pane or $300–550 for a standard single-story exterior. Hail is the market's recurring disruptor and it should be priced as a feature of the year rather than a surprise.
When is the best time of year to clean windows in Denver?＋
Denver's drier, frost-free months are July to September, by NOAA's 1991–2020 normals for the Denver-Stapleton station, where May brings the most rain. The calendar on this page marks July (after the April 30 bloom) and September (after smoke season and before frost). Frost nights usually run from October 8 to May 4. Normal highs reach 90°F in July.
Can I rinse windows with Denver tap water?＋
Yes, if the rinse is squeegeed off before it dries: Denver Water publishes dissolved solids of 91–225 mg/L, between this site's two dissolved-solids flags. It draws on two source systems of mountain snowmelt and reservoirs — the harder South Platte and the softer Moffat — treated at the Marston.
Why do my windows look dirty so quickly in Denver?＋
In Denver the dominant residue patterns include flash evaporation on sunlit glass at mile-high altitude and low humidity and front range hail grit and pitted screens. Altitude and dryness set the pace rather than mineral load.
Do I need a professional to clean my windows in Denver?＋
Working in high-altitude sun is the difficulty. On a large south or west pane the top dries before the bottom is finished, so a homeowner should work shaded elevations early and accept that the sunny side needs either shade, speed or someone with a pure-water system.
What sets Capitol Hill apart for window cleaning in Denver?＋
Mansion-row stock from the silver boom, with leaded and wavy glass in original sash. Dense street parking and narrow setbacks make equipment placement the constraint before the glazing does. LoDo / RiNo and Cherry Creek have their own housing stock and glazing as well.
Other cities we cover in Colorado
Nearby cities in neighboring states
Just over the Colorado line