Madison's deep sandstone aquifer water is extremely hard at 18 to 20 grains per gallon on the utility's figure, and it varies well to well across the city.
Madison's deep sandstone aquifer delivers extremely hard water with no softening at the plant, so glass that dries before the blade reaches it will mark, and a pure-water final rinse is the reliable fix. The water also varies from well to well across the city, and July to September is the dependable window. Lakeside homes in Shorewood Hills and Maple Bluff price on glass area, and a single-story exterior runs $300 to $550.
Madison's utility calls its own water very hard and puts it at 18 to 20 grains per gallon, over 300 mg/L, with no softening at the plant. At that level mineral deposit is the governing fact of the work rather than a finishing detail: glass that dries before the blade reaches it will scale, and on a hot isthmus afternoon that window is short. The sewerage district's wider figure of 15 to 32 grains across individual wells is worth knowing too, because it means the north and west of the city are not necessarily working the same water as the south.
Figures by source, as reported.
| Hardness | 308–342 mg/L as CaCO₃ Very hard — the utility applies the label itself, as published by Madison Water Utility. |
|---|---|
| Iron | 0–0.19 mg/L |
| Manganese | 0.002 mg/L (range 0–0.041) |
| Sodium | 12 mg/L (range 2.2–66) |
| Chloride | 32 mg/L (range 1–200) |
| Disinfectant | free chlorine |
| Source and treatment | 21 active wells drawing from a deep sandstone aquifer · Chlorination and fluoride addition at the wells; iron and manganese filters at four wells; a PFAS removal system at Well 15 since September 2025 · No softening step. |
Not in the report: pH, alkalinity, corrosion index and total dissolved solids.
SOURCE · Madison Water Utility Annual Water Quality Report (2025 testing), other substances table, with the utility's 2025 per-well water quality reports · How we source these numbers
Three overlapping loads. Mineral deposit is a constant and its magnitude is unmeasured here. The lake-driven organic film is a summer phenomenon and is worst on lakeside elevations in still, warm weather. Pollen follows the regional calendar, tree through spring and ragweed from August until frost. The longest-holding wash is a late-spring one away from the water; the least durable is a midsummer lakeside wash into algal season.
WISCONSIN SEASON BY SEASON →Madison is the outlier in this part of the Midwest and treating it as another lake city is the mistake to avoid. The supply is deep groundwater from sandstone wells, not lake water, and because different wells serve different parts of town the chemistry is not uniform across the city. The utility itself calls the water very hard — 18 to 20 grains per gallon, about 308 to 342 mg/L, in its FAQ — and its per-well reports show how much that moves, which is why a groundwater city's figure cannot be borrowed from the neighbours. What governs the work instead is geography and calendar: the isthmus holds humidity between two lakes so downtown dries slowly, summer algal activity puts a bonding organic film on lakeside glass that needs detergent rather than a rinse, and the university's turnover window concentrates a large share of the annual multi-occupancy work into a few predictable weeks. Freeze-thaw on the pre-war central stock is the one genuine damage risk, and it argues for washing with a dry-down window rather than merely above freezing.
Madison is the one city in this cohort that does not drink a Great Lake. The utility draws entirely from deep wells into the sandstone aquifer beneath the city rather than from either of the lakes it is built between, which is the single most important thing to know before planning a wash here — groundwater chemistry and open-lake chemistry are not the same problem.
That well-field structure also means the supply is not uniform across the city in the way a single-plant surface supply is. Different wells serve different parts of the distribution network, and a crew that calibrates its rinse on one side of town is not automatically calibrated on the other. This is unusual and it is worth checking rather than assuming.
Madison Water Utility answers the question on its own frequently-asked-questions page and does not soften the language: the tap water is very hard, containing 18 to 20 grains of hardness per gallon, which it attributes to the rock formations the wells draw from. That is roughly 310 to 340 mg/L, among the highest delivered figures anywhere on this site.
Being built on an isthmus is not a scenic detail, it is a drying constraint. With Mendota on one side and Monona on the other, the humidity over the older central neighbourhoods runs higher and holds longer than it does out on the west side, and the practical effect is that the same wash takes longer to dry downtown than it does four miles away on the same afternoon.
The lakes themselves generate a seasonal airborne load that most inland cities do not have. Summer algal activity on both lakes carries an organic film onto nearby glass, and it behaves differently from pollen — it bonds as it dries rather than sitting loose, so it wants a genuine detergent wash rather than a water-fed rinse.
The university sets the working calendar for a substantial share of the local book. The turnover window between spring and autumn terms is when campus-adjacent multi-occupancy stock can actually be worked, and that compresses a large volume of glass into a short predictable period every year. A crew that wants that work plans the rest of its summer around it.
Winter here is long and the freeze-thaw cycling on the pre-war isthmus stock is the maintenance risk worth naming to a client. Water introduced into a tired glazing bead during a warm afternoon and frozen overnight is what opens the bead, so on that housing the correct advice is to wash with a real dry-down window ahead, not merely on a day that happens to be above freezing.
Glass area drives the lakeside properties in Shorewood Hills and Maple Bluff. Access and drying time drive the isthmus, where a pane takes longer than its size suggests. The campus calendar drives everything else — it concentrates demand into a short window, and pricing inside that window reflects the fact that the work cannot be moved to a quieter month.
Hill Farms and the near west side are genuinely homeowner-workable. The isthmus is not, for two reasons that compound: the drying window is shorter there than the rest of the city and the sash are old enough that a scraper does real damage. Campus multi-occupancy is a contracted job on a fixed calendar, not something to take on one address at a time.
OPEN COST ESTIMATOR →2025 annual mean at the Madison - University AVE Well #6 monitor, 2757 University AVE, 1.7 km south of the city (EPA site 55-025-0047).
Largest air release: MGE West Campus Cogeneration Facility, 515 Walnut ST (electric utilities), inside the city limits, 41,848 lb in 2024.
The Madison Water Utility's general manager may impose voluntary or mandatory limits on outdoor water use across the utility's service area when supply or reserve capacity is under strain. The limits can cover every property or run on alternating sides of the street by calendar date.
Madison General Ordinances §13.04: outdoor water usage restrictions · checked September 2026
Madison bars anyone from discharging nonstorm water, or hooking a nonstorm water line to the storm sewer, without a permit. The ordinance exists to keep harmful material out of the lakes, streams and wetlands the storm sewers drain to.
Madison General Ordinances §7.47: regulations of discharge of nonstorm water · checked September 2026
A June 2025 rewrite turned Madison's Certificate of Appropriateness into a Certificate of Approval, which is required for the listed projects on landmarks, landmark sites and properties in its historic districts. The Preservation Planner issues it once an application is approved.
Madison General Ordinances §41.16: Certificate of Approval required · Madison General Ordinances §41.17: obtaining a Certificate of Approval · checked September 2026
Lake-effect snow loading on east-facing roof systems produces heavier ice-dam runoff than interior Wisconsin. Same chemistry and protocol Linnea Jorgensen documents for the Twin Cities: percarbonate prerinse, citric acid lift, attention to dwell times.
Milwaukee-specific. Neutralized iron-and-manganese leach plus cream-brick clay constituents stain glass below cream-city brick courses with a yellow-brown deposit pattern not documented elsewhere. Oxalic acid handling required; citric alone underperforms.
Deep-aquifer iron content produces orange-brown staining at sprinkler-overspray zones and on glass below copper or galvanized exterior fixtures. Oxalic acid required — converges with the protocol Elly Giordano documents for Piedmont iron-clay staining in North Carolina.
Madison runs on Madison Water Utility groundwater at a published 308–342 mg/L (CaCO₃) — very hard — the utility applies the label itself. Madison's utility calls its own water very hard and puts it at 18 to 20 grains per gallon, over 300 mg/L, with no softening at the plant.
Residential window cleaning in Madison typically runs $10–16 per pane or $300–550 for a standard single-story exterior. Glass area drives the lakeside properties in Shorewood Hills and Maple Bluff.
Madison's drier, frost-free months are July to September, by NOAA's 1991–2020 normals for the Madison Dane Regional Airport station, where June brings the most rain. The calendar on this page marks July (after the May 11 bloom and after smoke season). Frost nights usually run from October 10 to May 1.
Not as the final rinse: Madison Water Utility publishes hardness of 308–342 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. It draws on 21 active wells drawing from a deep sandstone aquifer.
In Madison the dominant residue patterns include deep sandstone-aquifer groundwater — very hard, 18 to 20 grains per gallon on the utility's own figure and well-to-well variation across the distribution network rather than one city-wide supply chemistry. Three overlapping loads. Mineral deposit is a constant and its magnitude is unmeasured here.
Hill Farms and the near west side are genuinely homeowner-workable. The isthmus is not, for two reasons that compound: the drying window is shorter there than the rest of the city and the sash are old enough that a scraper does real damage. Campus multi-occupancy is a contracted job on a fixed calendar, not something to take on one address at a time.
The narrow ground between Mendota and Monona, densely built and largely pre-war. Water on two sides means humidity holds longer here than on the west side, and the older sash and divided lights set the method more than the water chemistry does. Shorewood Hills and Maple Bluff and The campus edge and Langdon have their own housing stock and glazing as well.
Just over the Wisconsin line