Ann Arbor lime-softens a mix of Huron River and groundwater to an average of 126 mg/L, still hard, with the finished range running 74 to 180 mg/L.
Ann Arbor lime-softens a mix of Huron River and well water, yet it is still hard on average and moderately hard at best, so rinse water left to dry will spot. July to September is the working window, and campus move-out weeks squeeze a year of student-rental work into days. Historic districts take far longer per pane than their size suggests, and a single-story exterior runs $300 to $510.
The city's 2025 report gives finished-water hardness as 126 mg/L on average, across a range of 74 to 180, which it also prints as 7.4 grains per gallon — hard on average, reaching very hard at the top. That is after lime softening of a mixed Huron River and groundwater supply, so it is a plant setting rather than the river's own chemistry, and the same table shows chloride averaging 127 mg/L, high enough to matter on aluminium frames. Rinse water left to dry on dark glass will spot.
| Hardness | 74–180 mg/L as CaCO₃ Averaging 126 mg/L; hard, as published by Ann Arbor Water Treatment Plant. |
|---|---|
| pH | 9.3 (range 8.8–9.5) |
| Alkalinity | 54 mg/L as CaCO₃ (range 35–104) |
| Iron | not detected |
| Manganese | not detected |
| Sodium | 71 mg/L (range 59–96) |
| Chloride | 127 mg/L (range 99–170) |
| Disinfectant | ozone + chloramine |
| Source and treatment | Surface water, per the EPA SDWIS federal record · Pre pH adjustment, coagulation, flocculation, rapid mix, lime and soda ash softening with sedimentation and rapid sand filtration, granular activated carbon, pre-ozonation and ultraviolet radiation with chloramines as the residual, fluoridation and post pH adjustment · The plant softens. |
Not in the report: corrosion index and total dissolved solids.
SOURCE · Ann Arbor Water 2025 Consumer Confidence Report, Other Water Quality Parameters of Interest table · How we source these numbers
Organic load runs the calendar here. Tree pollen through spring, sap and leaf cast through the growing season and heaviest in late summer, ragweed from August until frost, then a long salt season on lower storeys. Mineral deposit is present but secondary; the softened supply runs 74 to 180 mg/L across the year. The campus stock has its own clock entirely and it is the summer turnover window.
MICHIGAN SEASON BY SEASON →Ann Arbor is a softening city and that governs how its water should be talked about. The municipal plant runs lime softening on a mixed Huron River and groundwater supply, so raw and finished hardness differ substantially — and the operator's own finished-water table now settles it: 126 mg/L on average, across a 74 to 180 range. That finished number is the one that matters, because raw and softened water here are not the same water. What actually drives the work here is organic rather than mineral: a dense tree canopy puts sap, leaf cast and pollen on upper sash in Burns Park and the older districts, and that responds to frequency and detergent, not to water chemistry. The market has two ends that barely touch — a campus rental belt whose entire annual cycle compresses into the summer turnover window, and the pre-1900 Old West Side where brittle putty and original glass make it slow, careful work.
Ann Arbor is a softening city, and that is the single most important thing on this page. The municipal treatment plant runs a lime softening process on its supply rather than simply filtering and disinfecting it, which means the water arriving at a tap here has been deliberately chemically altered to reduce hardness before it ever reaches a window.
That fact has a direct bearing on any figure quoted for this city. A softening utility produces a raw number and a finished number that differ substantially, and the figure used here is the operator's own finished-water average — 126 mg/L across 74 to 180 in 2025 — not a value picked up elsewhere that might describe the influent.
The supply is also genuinely mixed rather than single-source. The plant draws predominantly from the Huron River with a groundwater component from municipal wells, so the raw chemistry entering the process is not constant across the year, which is why the finished figure moves across a range rather than holding one value.
The academic calendar governs a larger share of this local market than in almost any comparable city. The student rental belt around central campus holds an enormous quantity of glass in multi-occupancy buildings that are effectively unworkable during term, so the entire annual cycle for that stock compresses into the summer turnover window. Crews that want it build their year around August.
The Old West Side is the technical counterweight to that volume work. A pre-1900 district of close-set frame houses means original glass, brittle putty and side access measured in feet rather than yards — slow, careful work at the opposite end of the trade from a campus rental block, in the same city and often in the same week.
The Huron River corridor and the city's unusually heavy tree canopy combine to make organic load the dominant residue here rather than mineral. Sap, leaf cast and pollen on upper sash in Burns Park and the older districts are what a homeowner actually complains about, and they respond to frequency and detergent rather than to anything done about the water.
Freeze-thaw on the pre-1900 stock is the damage risk worth naming to a client before work rather than after. Water driven into tired putty on a mild afternoon and frozen that night is what lifts the bead, so on the Old West Side the correct scheduling rule is a genuine dry-down window, not simply a day above freezing.
Access and glazing age drive the historic districts, where a pane takes far longer than its size implies. Volume and timing drive the campus belt, where the whole year's work must fit a few weeks and pricing reflects that it cannot be moved. Canopy is the quiet third factor: heavily shaded addresses need more frequent attention, and a quote that ignores the trees underprices the relationship.
Newer northern subdivision stock is reasonable homeowner work, with the standard coated-glazing warning about household cleaners. The Old West Side is not homeowner work — the putty is the fragile part and it is not obvious until it fails. Campus multi-occupancy is a contracted summer job with access requirements, not something to approach one building at a time.
OPEN COST ESTIMATOR →2025 annual mean at the Ypsilanti Towner ST, SOUTH; monitor, 555 Towner ST (Ypsilanti), 11.5 km east of the city (EPA site 26-161-0008).
Largest air release: Cayman Chemical Co Inc., 1180 E Ellsworth RD (chemicals), inside the city limits, 255 lb in 2024.
Ann Arbor's code lets the administrator of the public services area make regulations on the use of city water for any purpose, along with the rules for connections, meters and hydrants.
Ann Arbor City Code §2:31: additional regulations · checked September 2026
Ann Arbor's stormwater system exists to carry stormwater, and discharging non-stormwater into it is prohibited except for the uses the ordinance allows.
Ann Arbor City Code §2:215: use of stormwater system · checked September 2026
In an Ann Arbor historic district, a permit is required before any work that affects a building's exterior appearance, and the written approval of that permit as appropriate work is the certificate of appropriateness.
Ann Arbor City Code §8:412: permit applications · Ann Arbor City Code §8:407: definitions · 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.
The city's 2025 report gives finished-water hardness as 126 mg/L on average, across a range of 74 to 180, which it also prints as 7.4 grains per gallon — hard on average, reaching very hard at the top.
Residential window cleaning in Ann Arbor typically runs $10–15 per pane or $300–510 for a standard single-story exterior. Access and glazing age drive the historic districts, where a pane takes far longer than its size implies.
Ann Arbor's drier, frost-free months are July to September, by NOAA's 1991–2020 normals for the Ann Arbor Municipal Airport station, where May brings the most rain. The calendar on this page marks July (after the May 8 bloom and after smoke season). Frost nights usually run from October 4 to May 8.
Not as the final rinse: Ann Arbor Water Treatment Plant publishes hardness of 74–180 mg/L, enough to spot as it dries, so finish with pure water. Its sodium, up to 71 mg/L, leaves a salt film that pulls moisture back, so rinse it off rather than let it dry. Treatment starts with pre pH adjustment, coagulation, flocculation and rapid mix.
In Ann Arbor the dominant residue patterns include lime-softened municipal supply — finished water averaging 126 mg/l, hard and mixed huron river and groundwater raw supply, varying across the year. Organic load runs the calendar here.
Newer northern subdivision stock is reasonable homeowner work, with the standard coated-glazing warning about household cleaners. The Old West Side is not homeowner work — the putty is the fragile part and it is not obvious until it fails. Campus multi-occupancy is a contracted summer job with access requirements, not something to approach one building at a time.
A large pre-1900 historic district of close-set frame houses on a tight grid. Original sash, brittle putty and narrow side access together; careful work, and worth confirming the glazing before any tool comes out of the van. Burns Park and Kerrytown and the near downtown have their own housing stock and glazing as well.
Just over the Michigan line