Aurora blends Fox River and well water and lime-softens it to 110 to 160 mg/L, and the damp river corridor keeps downtown island glass slow to dry.
Aurora lime-softens a blend of Fox River and well water to moderately hard or hard, so spots show on glass that dries slowly, as it does in the damp river corridor downtown. The damp months drag on, so July to September carries most exterior work. Downtown's lit glass is judged at night, so detailing rather than washing drives that rate; a single-story home exterior runs $260 to $440.
The city's 2025 water quality report gives tap-water hardness as a range of 110 to 160 mg/L, which it equates to 6 to 10 grains per gallon — moderately hard at the low end and hard at the top. That is after the plant lime-softens a blend of Fox River water and well water, so the figure is a treatment result, and the proportions change with demand. Plan for real spotting on dark glass, heaviest when the blend runs to the top of the range.
| Hardness | 110–160 mg/L as CaCO₃ 6 to 10 grains per gallon in the city's own words, after lime softening at the plant; moderately hard to hard, as published by City of Aurora Water Production. |
|---|---|
| pH | 8.9–9.2 |
| Sodium | 57 mg/L |
| Disinfectant | chloramine |
| Source and treatment | Surface water with groundwater wells, per the EPA SDWIS federal record · Powdered and granular activated carbon and packed-tower aeration for taste and odour, permanganate, pre-chlorination and sequestration for iron and manganese, coagulation, flocculation, rapid mix, lime and soda ash softening with sedimentation and rapid sand filtration, chlorination with chloramines as the residual, fluoridation and post pH adjustment · The plant softens. |
Not in the report: alkalinity, corrosion index, iron, manganese, chloride and total dissolved solids.
SOURCE · City of Aurora Water Production Division 2025 Water Quality Report · How we source these numbers
Proximity to the river governs drying more than the month does, and the downtown island is the slowest ground in the city. Seasonally it is spring pollen, ragweed from August until frost and a moderate salt season. The commercial standard is effectively year-round, because illuminated frontage makes an imperfect finish visible every night rather than only in low sun.
ILLINOIS SEASON BY SEASON →Aurora blends Fox River surface water with well water and lime-softens the blend, and the city's 2025 report gives the result as a range rather than a point: 110 to 160 mg/L, or 6 to 10 grains per gallon. A range is the honest shape for a blended system, because river water moves with rainfall while aquifer water is steadier, so the tap shifts as the blend shifts with demand. The city's shape matters more than its chemistry anyway. The commercial core sits on an island in the river, so downtown glass has water on two sides and dries slower than the grid a few blocks inland, which argues for working the island early and the western subdivisions late. The city's long-standing electric street lighting left it a downtown built to be seen after dark, and illuminated frontage shows streaking daylight hides — the acceptable finish on commercial glass here is higher than the pane count implies. The historic districts combine period sash with tight access, so suburban productivity assumptions fail there.
Aurora runs a genuinely split supply and that is the reason a single number would misdescribe it. The city treats Fox River surface water at its own plant and also draws from wells, so the water at a given address depends on which part of the network serves it rather than on one city-wide chemistry.
A surface component and a groundwater component do not merely differ in hardness, they differ in how they vary. River water moves with rainfall and season while aquifer water is comparatively steady, so a blended system's chemistry shifts as the blend shifts — and the blend shifts with demand.
That is why the city publishes a range rather than a single figure: 110 to 160 mg/L at the tap in 2025, after lime softening at the plant. The range is the useful number; an average would hide the swing.
The city is built across the Fox River with its commercial core on an island in the middle of it, which is an unusual arrangement with a practical consequence. Downtown glass has water on two sides and dries measurably slower than the grid a few blocks away, so the sensible route order puts the island work early and the western subdivisions late.
Aurora was among the first cities in the country to light its streets electrically and has carried the nickname ever since, and the visible legacy is a downtown built to be looked at after dark. Illuminated frontage shows streaking that daylight hides, which raises the acceptable finish standard on commercial glass here above what the pane count would suggest.
The historic east and west side districts carry the oldest glazing and the tightest access in the city together. Nineteenth-century sash on narrow lots with little setback means a crew spends as much time positioning as washing, and pricing that assumes suburban productivity will not survive the street.
Being the second-largest city in the state without being a suburb of the largest gives the local market an unusual shape — a full commercial core of its own alongside a large commuter-belt residential book, which lets a crew here hold both kinds of work without leaving the city.
Finish standard drives the downtown rate, since illuminated glass is judged at night and the detailing rather than the washing is where the time goes. Access drives the historic districts. Pane count drives the western subdivisions. Holding both a commercial core and a commuter residential book inside one city is what lets local crews balance the seasonal closure.
Far west subdivision stock is straightforward homeowner work with the usual caution about coated units. The near east and west side historic streets are not, because period glazing and cramped access compound each other. Downtown island frontage needs a finishing pass that most homeowners will not achieve and will notice failing after dark.
OPEN COST ESTIMATOR →2025 annual mean at the Kane County Health Dept monitor, 1240 N. Highland AVE., 4 km north-west of the city (EPA site 17-089-0007).
Largest air release: Crown Aerosol Packaging, 3737 E Exchange AVE (fabricated metals), inside the city limits, 17,785 lb in 2024.
Aurora places every hydrant under its public works director; apart from firefighters, only people the director authorizes may open one, and they must first put down a deposit of twice the cost of a hydrant water meter and draw water through that meter, returning it in the same condition.
Aurora Code Sec. 48-29: hydrant jurisdiction; use · checked September 2026
Aurora forbids anyone to discharge or let enter, directly or indirectly, the Fox River or any other watercourse in the city any liquid that will pollute or defile it, and makes it unlawful to set up any connection that lets polluting substances into a stormwater sewer. Dirty, soapy rinse water sent down a street inlet reaches the river that way, so collect it instead.
Aurora Code of Ordinances Sec. 48-131: discharges into sewers and the Fox River, generally · Aurora Code of Ordinances Sec. 48-134: polluted wastes connected to stormwater sewers · checked September 2026
Aurora's preservation chapter forbids any alteration to a designated landmark, or to a property inside a historic or urban conservation district, unless a certificate of appropriateness has been granted by the preservation commission or its designee; the commission weighs changes to the essential character of the area, which covers visible window replacement.
Aurora Code Sec. 37-61: jurisdiction of commission with respect to alterations · Aurora Code Sec. 37-62: standards and criteria for a certificate of appropriateness · checked September 2026
Atomized chloride from winter road treatment. Migrates onto residential glass for blocks downwind of any salted artery. The post-winter cleanup pass in March or April is the largest single residential cleaning category in Chicago.
The first warm weeks after ice-off produce a thin algal-bloom aerosol on the Chicago lakeshore. Local to within a mile of the water. Manifests as a faint green tint at the glazing edge.
The city's 2025 water quality report gives tap-water hardness as a range of 110 to 160 mg/L, which it equates to 6 to 10 grains per gallon — moderately hard at the low end and hard at the top. That is after the plant lime-softens a blend of Fox River water and well water, so the figure is a treatment result, and the proportions change with demand.
Residential window cleaning in Aurora typically runs $8–13 per pane or $260–440 for a standard single-story exterior. Finish standard drives the downtown rate, since illuminated glass is judged at night and the detailing rather than the washing is where the time goes.
Aurora's drier, frost-free months are July to September, by NOAA's 1991–2020 normals for the Aurora station, where May brings the most rain. The calendar on this page marks July (after the May 5 bloom and after smoke season). Frost nights usually run from October 23 to April 19.
Not as the final rinse: City of Aurora Water Production publishes hardness of 110–160 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. Treatment starts with powdered, granular activated carbon, packed-tower aeration for taste and odour.
In Aurora the dominant residue patterns include blended fox river and well supply, lime-softened to 110–160 mg/l — moderately hard to hard and river-corridor damp and slow dry-down, sharpest on the downtown island. Proximity to the river governs drying more than the month does, and the downtown island is the slowest ground in the city.
Far west subdivision stock is straightforward homeowner work with the usual caution about coated units. The near east and west side historic streets are not, because period glazing and cramped access compound each other. Downtown island frontage needs a finishing pass that most homeowners will not achieve and will notice failing after dark.
The commercial centre built on an island in the Fox River, with ornate early twentieth-century frontage and significant decorative glazing. Water on both sides means slower dry-down than the surrounding grid. Near East Side historic streets and Near West Side have their own housing stock and glazing as well.
Just over the Illinois line