Window cleaning in Illinois: the divided state, road salt, and the cottonwood problem

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I. The divided state

The first thing to understand about cleaning windows in Illinois is that there is no such thing as cleaning windows in Illinois. There is cleaning windows in Chicago, which is one trade with one water profile and one customer base and one set of seasonal problems, and there is cleaning windows in the collar counties and downstate, which is a different trade with different water and a different customer base, and the two are separated by a line that is invisible on a road atlas but loud on the side of every glass surface I touch.

The line follows the boundary of the Lake Michigan service area. Inside it — the City of Chicago Department of Water Management directly, or lake water resold through the DuPage Water Commission, the Northwest Water Commission and the smaller wholesalers — the supply is Chicago's, at a published 126–143 mg/L (hard). The sprinkler overspray on your patio doors, when it dries, leaves a faint film that wipes off with the same protocol I'd use in St. Louis or Cincinnati.

Outside it, the water belongs to whichever system serves the house. Aurora sits at a published 110–160 mg/L and Springfield at a published 80–142 mg/L, so the protocol follows the city's own figure rather than a statewide assumption, and a private well needs its own test.

I have been cleaning glass in this state since 2014. I started on a small residential route in Logan Square, picked up commercial work in 2017 after I got serious about pole technique, and have spent the last six years running the senior editorial seat at this publication while still maintaining a half-route of long-term residential clients on the North Side. I have also, in the course of writing this piece and the others like it, spent significant time in the field with cleaners in Naperville, Aurora, Joliet, Rockford, and Springfield. The thing I have learned, slowly and against my own initial assumption, is that the protocols I built up over a decade on Chicago glass are not transferable as written to most of the rest of the state. The technique transfers. The chemistry does not. The expectations of how a window should look ten minutes after cleaning, and ten days after cleaning, also do not transfer, because they are downstream of the water.

This piece is the long version of that lesson. I am going to walk through the water, the road salt, the seasonal contaminants, the freeze-thaw calendar, and the way the trade actually operates in Illinois in 2026. If you are a homeowner trying to figure out why the windows in your new house in Naperville will not stay clean the way the windows in your old apartment in Wicker Park did, this piece is for you. If you are a cleaner moving from one part of the state to the other and wondering why your routes feel different, this is for you also.

II. The water, in detail

Chicago and its inner-ring suburbs draw from two filtration plants — Jardine, on the lakefront just north of Navy Pier, and South Water, near 79th Street. Both plants pull from intake cribs that sit about two miles offshore in Lake Michigan, in roughly thirty feet of water, where the lake stays cold and clear and remarkably consistent in composition. Year to year, season to season, week to week, it does not move much. The water has other complications — the chloramine disinfection regime can leave a faint film at the edge of a glazing bead if a homeowner is using tap water and a microfiber and nothing else, and the source water carries a small but measurable amount of organic matter from the lake that shows up as a yellow tint in long-term standing puddles — but the calcium content is what it is, Chicago at a published 126–143 mg/L (hard), and you can plan around it.

Now move thirty miles west.

The collar counties — DuPage, Kane, Will, McHenry, Lake (the inland portion), and the western edges of Cook — sit over the Cambrian-Ordovician sandstone aquifer system, a deep sedimentary water source that has supplied this region's wells for a hundred and fifty years. Naperville pumps from that aquifer. Aurora blends Fox River surface water with deep sandstone groundwater. Joliet is on it almost entirely. The water from those deep-well systems is a different chemistry from Chicago tap, and where a collar-county system has not switched to DuPage Water Commission Lake Michigan supply, its own annual report is the figure to work from.

The difference shows up on every surface that water touches. A sprinkler hits the lower third of a Naperville patio door once a day for a summer, and by August there is a chalky white band across the glass that a clean-water rinse will not remove. The same sprinkler in Lincoln Park leaves a film you can squeegee off in your sleep. The protocol is the same. The result is different because the chemistry is different.

If you are working in the collar counties, you adjust. Pre-treatment with an acidic dissolver is standard on any glass that has lived through a summer of overspray — I use a citric-acid blend at five percent for moderate buildup and a phosphoric blend at three percent for the cement that forms in the second or third summer of neglect. (Phosphoric is faster but you have to rinse it off the masonry or it will etch limestone trim, and a lot of collar-county housing has limestone trim.) Pure-water-on-the-pole, with deionized water dispensed through a brush, is the better long-term answer for routes that run through this hardness, because every spray of tap water that hits the glass without being squeegeed off is adding to the problem you'll have to remove next time. I have a piece on the way the hard-water-spots-ranked — Drew Giordano wrote it from the Phoenix end of the spectrum, but the principles read the same in Joliet.

A note on Naperville, because it is its own case. Naperville switched a large portion of its supply to DuPage Water Commission Lake Michigan water in the 1990s, but the legacy deep-well infrastructure was not fully retired, and parts of the service area still see a blend. The result is that hardness can vary from one neighborhood to the next, sometimes one block to the next, depending on which trunk main feeds the house. Saybrook and Ashbury can read very differently within the same month. If you are running a route through Naperville, you cannot assume a single hardness. You have to test the first time, and you have to be ready to switch protocols mid-route.

Joliet is on its own clock. The city has been pumping deep sandstone water since the eighteen-eighties, and the aquifer has been declining for fifty years. The city is under court order to be on Lake Michigan water by 2030, which will resolve the hardness problem, but until then Joliet's deep wells set the work on Joliet glass, and Joliet publishes no figure the site uses. Rockford runs on shallow and deep sandstone wells and publishes no figure either. Springfield, on Lake Springfield surface water, sits at a published 80–142 mg/L (moderately hard to hard), which reaches below Chicago at the low end.

The summary, if you want one line: Illinois splits cleanly along a water-source line. Everywhere else, check the local report: Aurora sits at a published 110–160 mg/L (moderately hard to hard), and the well towns publish nothing the site can use.

III. Road salt: the largest single residential category

If you had asked me ten years ago what the biggest single driver of residential window-cleaning demand in the Chicago metro was, I would have guessed pollen, or maybe pre-holiday cleaning, or maybe the post-construction work that comes out of the always-active North Side renovation market. I would have been wrong on all three. The biggest single driver is road salt.

Chicago uses, in an average winter, around four hundred thousand tons of road salt across the city's six thousand lane-miles of arterial and residential streets. The collar counties together use roughly the same. The salt is applied as solid rock salt and as pre-treated brine — calcium chloride and magnesium chloride blends that the Illinois Department of Transportation and the municipalities have shifted to over the last decade because they activate at lower temperatures and stick to the road longer. The brine, in particular, is the problem.

When a truck moves through residential streets at twenty-five miles an hour spraying brine onto pavement, the brine atomizes in the slipstream behind the truck. The atomized droplets carry chloride salts in solution, and they drift. They drift on the wind for a block or two. They settle on car windshields, on parked-vehicle paint, on house siding, and on the lower courses of residential windows. They settle especially on windows that face the street, on first-floor and basement glazing, and on any window within about thirty feet of a salted arterial road.

The chloride does not wash off in normal rain. Chloride is hygroscopic — it pulls water out of the air — and once it has bonded to a glass surface and gone through a few wet-dry cycles, it has worked into the very top layer of the glass and into any micro-pitting that exists in the older glazing. It manifests as a haze. The haze is most visible in the low winter sun, raked across the glass at a shallow angle, and it is the single most common reason a Chicago homeowner picks up the phone in February and March.

I have spent a lot of time thinking about the right protocol for road-salt cleanup, and I have settled on this one: a generous flood with deionized water if you have it, or with filtered tap if you don't, applied with a strip washer at full saturation and left to dwell for two or three minutes. The water dissolves the chloride back into solution. Then a clean squeegee pass, with the rubber wiped between every stroke, because the dissolved chloride will redeposit on the rubber and streak the next pass if you do not wipe. Then a second pass with fresh solution. Sometimes a third on the worst panes. The work is slow, more like an etching-removal job than a routine cleaning, and I price it accordingly.

The window when this work happens is the post-thaw period — from about the first week of March, depending on the winter, through the first week of May. By the second week of May, the salt is mostly gone, the spring pollen is starting, and the residential market shifts into its general spring cleaning rhythm. But for those eight or nine weeks, salt is the work. The phones ring constantly. Routes that have been dormant since mid-December come alive in a rush.

If you are reading this as a homeowner, the practical advice is to schedule your spring cleaning for late March or early April rather than the second week of February when the windows first start to bother you. February cleanings get re-salted within a week. March cleanings hold, because the salt application has effectively stopped for the year and the residue can be removed without immediately being replaced.

IV. What else lands on the glass, season by season

Road salt is the dominant residential contaminant but it is not the only one. The Illinois cleaning calendar has its own particular shape, and the contaminant profile shifts every six to eight weeks.

April through May is the oak pollen window. The Chicago region's oak canopy — the bur oaks and white oaks that line the parkways from Evanston down through the South Side, and the second-growth oak stands across the collar counties — produces a thick yellow-green pollen dust through April and into the first half of May. The pollen is sticky. It adheres to glass with a slight resinous backing, and a plain-water rinse will not remove it. A surfactant pass — a drop of dish soap in a gallon of water, or a proper window-cleaning solution — releases the pollen and lets the squeegee carry it off. The pollen overlaps the tail end of the road-salt season, which means April is the busiest month of the year for most established Chicago routes. I block out April for residential work and decline most new commercial bids until May.

Late May through mid-June is cottonwood. This one is specific to Illinois and a handful of other Midwest states with a serious cottonwood population, and it is the contaminant nobody outside the region understands until they have lived through it. Cottonwood trees — the eastern cottonwood, Populus deltoides, which lines almost every Illinois waterway and stands as parkway trees throughout the older Chicago neighborhoods — release their seeds in late spring, and each seed is wrapped in a tuft of white cotton-like fluff that floats on the wind. For about three weeks, the air is full of it. Cottonwood fluff piles up against window screens, gets caught in the spider work at the edges of patio doors, and sticks to glass. The fluff itself is not the cleaning problem — it wipes off easily. The problem is that each seed has a small resinous backing that the fluff is attached to, and when the fluff blows off, the resin stays. The resin sets into a small brown spot on the glass that resists water and resists most surfactants. The right treatment is a citrus-based solvent applied with a microfiber, dwelled for thirty seconds, then squeegeed off as part of the normal cleaning pass. I have a longer treatment in the article on the solvent ladder — the cottonwood resin sits about three rungs down from pine sap, somewhere between bug splatter and tree sap proper.

Summer in Chicago is relatively kind to glass. The humidity is moderate to high, but the glass temperatures stay manageable — even on the south side of a black brick three-flat in July, the surface temperature rarely exceeds a hundred and twenty Fahrenheit, well below the threshold where solution flash-evaporates in the middle of a squeegee stroke. Lake-effect cooling moderates the shoreline neighborhoods further, knocking five to ten degrees off Loop temperatures any day the wind has an easterly component. I do most of my July and August work in the morning before the afternoon onshore breeze fills with whatever industrial particulate has been sitting downwind of the South Works, but the cleaning itself is straightforward in this season.

September through early November is the second peak. The pollen is gone, the cottonwood is long gone, the heat is breaking, and homeowners are scheduling pre-holiday cleaning. Leaves are coming down, which produces tannin staining on glazing beads where wet leaves have rested for a few days against the bottom of a window — tannin reads as a brown smudge that wipes off with plain water but leaves a faint stain behind that needs an oxalic-acid treatment to fully clear. Cooler glass temperatures make solution work easier. The light has shifted to the low autumn angle, which makes every imperfection visible, which is why this is the season homeowners notice things they did not notice in July.

Late November through mid-December is the pre-holiday rush, compressed into about three weeks. Most established routes are fully booked in this window. After mid-December, the residential market closes for the winter — which is its own section.

V. The freeze-thaw calendar and the closed winter market

You cannot clean residential windows in Chicago between mid-December and mid-February. Or rather, you can, but the work product is not a clean window. The work product is a sheet of ice with vertical streaks.

The reason is straightforward: cleaning solution freezes on contact with glass below about twenty-eight Fahrenheit, depending on the surfactant load and the glass temperature. The squeegee, dragging across glass at single-digit ambient temperatures, leaves a thin film of solution that ices over before the next stroke can clean it up. The result is a window that looks worse than the one you started with, and a customer who, reasonably, does not pay. There are antifreeze additives — methanol blends mostly, and some specialty propylene-glycol products — that extend the working range down to about fifteen Fahrenheit, but the additives are toxic to plants and pets, they smell, and they are unpleasant to work with for any prolonged stretch. The honest move, for residential, is to close the route for eight to ten weeks and let the customers know the schedule resumes in March.

Most of the established Chicago operations do exactly this. The winter income comes from interior commercial — office buildings, hotels, restaurants — and from a small amount of storefront work that can be done in the brief above-freezing windows. The high-rise window-cleaning operations stay active year-round because the building exteriors at altitude are exposed to wind and chloride mist all winter and the boards have maintenance budgets that don't pause. But for residential, the winter is closed, and any operation that promises year-round residential service in Chicago is either using methanol products and undercharging or is going to disappoint their customers.

This calendar has consequences. It compresses the residential year into about thirty-six weeks instead of fifty-two. It concentrates demand into the spring and fall peaks. It means that the average Chicago residential cleaner needs to earn a year's living in nine months, which is one of several reasons the labor cost in this trade is what it is. It also produces a particular kind of glass damage that I see every March: the freeze-thaw cycle, repeated thirty or forty times over a winter, works its way into any micro-crack in older glazing and into any compromised seal, and by the time the spring cleaning pass arrives, the cleaner is the first person to notice that the bottom seal on the Pella double-hung in the kitchen has failed and the IGU is fogging. We report a lot of failed seals every March. The homeowners do not always thank us, but we report them.

A subsidiary point: the freeze-thaw cycle also damages exterior caulk and putty around older wood-sash windows. A spring cleaning pass is, for a pre-war housing stock client, often the first time anyone has looked closely at the exterior glazing in six months, and the pre-spring report on caulk condition is a value-add I include with every March residential job in Lincoln Park or Logan Square. Some of those houses still have their original 1920s wood sash. The glazing putty is a hundred years old. It does not always make it through another winter, and the cleaning pass is when that gets caught.

VI. The big cities, briefly

Chicago runs on Lake Michigan water at a published 126–143 mg/L (hard). The housing stock is dominated by pre-1940 multi-family masonry — three-flats, six-flats, courtyard buildings — with original double-hung wood-sash glazing in a meaningful portion of the inventory. Lincoln Park, Logan Square, Pilsen, Hyde Park, and the older Oak Park stock are the heaviest concentrations of pre-war single-pane wood-sash work. The water is forgiving; the housing stock is not. Working on hundred-year-old wood sash requires a different approach than working on modern vinyl — gentler chemistry, more careful pressure on the glazing bead, and an eye for the failed putty that the freeze-thaw has exposed.

Aurora runs on a blend of Fox River surface water and deep sandstone groundwater, at a published 110–160 mg/L (moderately hard to hard). The housing stock is a mix — older downtown in the historic district, large post-1990 developments in Stonebridge and the Far East Side, and a meaningful concentration of Fox Valley mid-century brick ranches. Sprinkler-overspray work is heavy here. Routes that run Aurora carry an acidic dissolver as standard equipment, where Chicago routes carry it for special cases.

Naperville is the variable-hardness town I mentioned earlier — partly on Lake Michigan supply, partly on legacy deep wells, depending on the trunk main. The housing stock skews newer — large post-1990 single-family on lots of half an acre or more, with full irrigation. Sprinkler-overspray on the lower third of patio doors is the consistent residential problem. Test your first job at a new address; do not assume.

Joliet runs on deep sandstone groundwater, with a court-ordered switch to Lake Michigan water by 2030. Until then, its deep-well water is its own problem, and it publishes no figure the site uses. The housing stock is mixed — older downtown stock, a band of mid-century, and large post-2000 developments on the outskirts. The work is what the water makes it.

Rockford runs on shallow and deep sandstone wells, with elevated iron in some service zones. The iron produces an additional staining pattern on north-facing window trim that I do not see anywhere else in the state — a faint orange shadow at the corners of glazing beads, in particular, that needs an oxalic-acid pass to fully clear. The housing stock is heavily mid-century single-family and a meaningful pre-war downtown.

Springfield runs at a published 80–142 mg/L (moderately hard to hard) on Lake Springfield surface water. Seasonal algal blooms in the lake occasionally change the taste of the water, but the cleaning hardness stays steady. The housing stock concentrates in pre-1940 single-family in Aristocracy Hill and the Vinegar Hill historic district, with newer developments on the city's western edge.

VII. What the local trade looks like in 2026

The Chicago metro has, by my count, somewhere between four hundred and six hundred active residential window-cleaning operations of one to ten employees, plus a smaller number of larger commercial-and-high-rise operations. The trade is fragmented. Most operators run small — one or two trucks, a route built up over a decade of word-of-mouth, and a customer base concentrated in a few neighborhoods. The collar counties have their own ecosystem of larger franchise operations and smaller independents.

The pricing has held up well in real terms since I started. A standard Chicago bungalow exterior — twelve to sixteen windows, single-pane wood sash, mid-grade complexity — runs two-fifty to three-fifty in 2026. A three-flat exterior runs four-fifty to six. A standalone Lincoln Park graystone with original 1900s windows and a tricky setback runs higher. Collar-county work prices similarly on a per-window basis but tends toward larger jobs — bigger houses, more windows per address — so the average ticket runs higher.

The biggest shift in the trade over the last decade has been the adoption of pure-water-on-the-pole for residential exterior work. Ten years ago, almost everyone was on traditional squeegee technique for residential. Today, a meaningful portion — I'd estimate forty percent — of the residential exterior market is being cleaned with deionized water through a carbon-fiber pole and a soft brush, no squeegee touching the glass at all. The shift was driven partly by labor (pole work is faster and less physically demanding than ladder work) and partly by the hardness gradient I described earlier (in the collar counties, deionized water solves the overspray problem at the source). The traditional squeegee work has retreated to interiors, to the high-rise commercial market, and to the historic-housing-stock segments where the housing detail rewards the close inspection that ladder work provides.

If you are reading this as a homeowner deciding between cleaners, my honest take is this: ask which technique they use. If they say pole-and-pure-water, ask whether they squeegee the interiors with traditional technique. If they say traditional everywhere, ask whether they pre-treat for hardness in the collar counties. The right answer depends on your water and your housing stock, and a cleaner who has thought about the question is usually a better hire than one who has not.

VIII. What to do about all of this

I have spent a lot of words on the problems. The practical question, if you live in Illinois and you would like your windows to look clean, is what to actually do about it. Here is what I would tell you in the kitchen.

Know your water. If you are in Chicago or an inner-ring suburb plumbed into Lake Michigan supply, your water is the published 126–143 mg/L Chicago supply (hard) and your cleaning protocols can be simple. If you are anywhere else, look up your municipal water-quality report — every utility publishes one annually — and find the calcium hardness number. The piece on hard water etching versus deposits explains the difference between mineral deposits that will come off and etching that will not.

Time your cleaning to the calendar. The right time for the spring pass is late March through April, after the salt application has stopped and before the heaviest pollen. The right time for the fall pass is late September through October, before the leaves are fully down. Avoid February cleanings unless you have a specific reason — they will be re-salted within a week. Avoid late June through July cleanings if you are in a heavy cottonwood neighborhood — wait until the seed fluff has finished.

Address sprinkler overspray at the source. If you have an automatic irrigation system that is hitting your windows, the right move is to adjust the heads before you call a cleaner. No cleaning will hold if the sprinkler is rebuilding the deposit every morning. I have lost count of the number of jobs where the customer wanted the windows cleaned and the right answer was to call the sprinkler company. The article on humidity, hysteresis and the cleaner you cannot see covers this from the squeegee end; the real fix is upstream.

Match the technique to the housing stock. Pre-1940 wood-sash windows want a gentle approach — soft strip washer, light squeegee pressure, careful work around the glazing bead. Modern vinyl-frame windows can take more pressure and faster work. If your house is mixed — many older Chicago homes have a mix of original sash on the front of the house and replacements on the back — let the cleaner know, and expect different per-window times for the two halves of the job.

Use the right squeegee, with fresh rubber. I have written a long piece on the squeegee — squeegee anatomy, technique, and the rubber problem — and the central point of that piece is that the rubber wears out faster than most people understand. If you clean your own windows, replace your squeegee rubber every few months, not every few years. If you hire someone, watch them once. If their rubber looks chewed and they don't have spares in the truck, they are not the right hire.

Read the basic technique piece. how to wash a window properly covers the four stages — preparation, washing, squeegeeing, detailing — and the four stages apply equally in Lincoln Park and in Joliet. The chemistry changes; the sequence does not.

Know what your glass is. Tempered glass, low-E coated glass, and older single-pane float glass all clean differently. The glass types and cleaning piece covers the distinctions. The piece is most relevant in newer construction with low-E coatings that can be damaged by improper cleaning protocols, which describes a lot of the housing stock built in the collar counties since 2000.

That is the long answer. The short answer is that Illinois is two states for the purposes of window cleaning, the line runs along the edge of the Lake Michigan service area, and the protocols that work on one side of the line need adjustment to work on the other. If you understand that, and you time your cleaning to the seasonal calendar, and you adjust your sprinkler heads, the windows in your house can look good year-round.

Except mid-December through mid-February. Nothing helps then.

Streak-free is a chemistry problem. So is everything else in this trade. I have been working on the chemistry for twelve years and I am still finding new corners of it. Illinois has been a generous teacher in that regard.