Guide · updated October 13, 2026
Hard-water spots on windows: what causes them near Ontario and how to remove them
Why windows in the Inland Empire get white rings, which cities have the hardest water by their own water reports, what you can safely try yourself and when a photo quote makes more sense.
Short answer: the white spots are minerals left behind when sprinkler water dries on the glass. Fresh spots usually wipe off. Old, thick ones need a vinegar soak, and the oldest can etch into the glass for good. The best fix is to stop the sprinkler from hitting the window.
Water in the cities around Ontario ranges from moderately hard to very hard. The table below lists what each water supplier reported. If your windows have heavy crust, tell us in your quote request and we will text you for a photo. We quote the removal from the photo, from about $6 a window on top of a normal clean, and never add it without asking.
What the spots are
Tap water carries dissolved calcium and magnesium. When a drop dries on glass, the water leaves and the minerals stay. One sprinkler cycle leaves a faint ring. Hundreds of cycles stack into a white crust. Glass Doctor, a glass repair brand, describes the same thing: as water evaporates it leaves minerals behind, and it asks whether a sprinkler is close by and spraying the windows. It adds that some spotting can etch into the glass over time.
The U.S. Geological Survey links hard water to spots and film on dishes and glassware and calls the residue not dangerous but unsightly. It sorts water by hardness, in milligrams of calcium carbonate per liter (mg/L): soft is 0 to 60, moderately hard is 61 to 120, hard is 121 to 180 and very hard is anything above 180. Some water suppliers report in grains per gallon instead. One grain per gallon is 17.1 mg/L, so 180 mg/L is about 10.5 grains.
How hard is the water near Ontario?
The Ontario Municipal Utilities Company provides the City's domestic water supply.
Each supplier prints its own annual water quality report. We read the newest one for each city we serve and list the hardness it printed. Suppliers sell water from more than one source, so many cities show a range, and the report usually does not say which streets get which water. Treat this as a map of the area, not a measurement of your tap.
Pomona's table is from its report published in 2024, the latest we could open. Norco's covers 2024. Walnut is also served by Suburban Water Systems, whose 2024 report lists averages near 188 and 215 mg/L. Details and links are on each city page.
The pattern: nearly everywhere is at least moderately hard, and a good part of the area sits in the "very hard" band. Where your supplier blends in imported water, hardness drops. Where it pumps local wells, it rises.
Why sprinklers are the main cause
A sprinkler head that wets the same window each morning leaves a ring in the same spot every day, and WeatherSpark's modeled data puts Ontario's rainless period at April 22 to October 20, so there is no rain to wash it off. The usual signs are a white band along the bottom of ground-floor windows, a fan shape where the spray reaches, and spots that return a day after you clean them.
Cement and stucco runoff is a second source worth knowing about. Architectural glass maker Viracon says concrete or mortar slurry is extremely alkaline and will eventually etch the glass surface. Rinse it off right away after masonry or stucco work.
What to try yourself, and what not to
- Start with the mildest option. Viracon recommends a mild, non-abrasive, non-alkaline cleaner, a grit-free cloth, a rinse and a squeegee. That handles fresh spots.
- White vinegar. Glass Doctor suggests spraying equal parts water and white distilled vinegar, letting it sit, scrubbing, drying and repeating as needed. It works on light to medium spotting. Do not use vinegar on solar panels unless your panel manual allows it.
- Do not use razor blades or scrapers. Viracon says razor blades and scrapers can scratch glass. Scouring pads are the same risk.
- Do not use strong alkaline cleaners. Viracon recommends non-alkaline cleaners (see above).
- Dry the glass. Spots form as water dries. A squeegee or microfiber cloth after rinsing keeps minerals from drying in place.
- Stay off ladders. Upper windows are the ones that tempt people onto a ladder. A water-fed pole from the ground gets to them without one.
If vinegar and a few rounds of work do not lift the crust, it may have started to etch. Glass Doctor says glass permanently damaged by hard-water spots can mean replacement is the only option. That is the reason to deal with spots early.
How to stop them coming back
- Aim or move sprinkler heads so they stop wetting glass. A few inches can be enough. Spray shields help.
- Wash on a schedule. Fresh spots are the easy kind. A plan every 3 months keeps them from stacking.
- Finish with pure water. A pole that feeds pure water to a soft brush rinses without leaving minerals. Unger, which makes window tools, says pure-water pole cleaning works without drying and polishing. This is how we clean.
- Ask about a hydrophobic coating if you want to cut the water that clings to glass. Glass Doctor says hydrophobic coatings create a protective barrier that repels water. We do not apply coatings.
What we charge for spots
A normal clean at $9 a window removes light spotting. Heavy crust takes extra time, so we quote it from a photo, from about $6 a window on top. Housecall Pro, a pricing guide written for window cleaners, says extras like screens, tracks or hard-water stain removal run $2 to $30 each. We tell you the number first. We do not add it without your OK. See the window cleaning cost guide for the full price list.
Common questions
What causes white spots on windows?
Minerals, mostly calcium and magnesium, left on the glass when sprinkler or hose water dries. The harder the water, the more it leaves.
How do I remove hard-water spots from glass?
Spray equal parts water and white vinegar, let it sit, scrub with a soft cloth, dry and repeat. Do not use razor blades or abrasive pads, which can scratch glass. Fresh spots often come off with a normal wash.
Can hard water damage window glass?
Left for a long time, spots can etch into the surface and become permanent. Glass Doctor says severe etching can require glass replacement.
How hard is the water where I live?
It ranges from moderately hard to very hard across the cities near Ontario. The table in this guide lists what each supplier reported. Check your own supplier's latest report for your address.
Do you charge extra for hard-water spots?
Light spotting comes off in a normal clean. Heavy crust is quoted from a photo, from about $6 a window on top, and we do not add it without asking.
Where this applies
We work in every place within 15 miles of Ontario: Ontario, Upland, Montclair, Chino, Rancho Cucamonga, Claremont, Alta Loma, Eastvale, Pomona, Etiwanda, Chino Hills, Jurupa Valley, La Verne, Norco, Fontana, San Dimas, Diamond Bar, Corona, Walnut, Rialto, Covina, Glendora.
Related services: Window cleaning, Plans, Instant quote.
More guides
- Window Cleaning Cost in the Inland Empire
- How Often to Clean Solar Panels in the Inland Empire
- Santa Ana Winds, Dust, Windows and Solar Panels
Sources
- Glass Doctor, "How to remove water spots from windows" (sprinkler minerals; vinegar mix; etching; prevention). “as water evaporates, it leaves behind minerals that build up and create chalky white deposits”
- Glass Doctor, "How to remove water spots from windows" (sprinkler minerals; vinegar mix; etching; prevention). “over time, can etch into the glass surface”
- USGS Water Science School, "Hardness of water" (classes in mg/L; hard water, spots and film). “spots or film on them? this is more hard-water residue-not dangerous, but unsightly”
- USGS Water Science School, "Hardness of water" (classes in mg/L; hard water, spots and film). “0 to 60 mg/l (milligrams per liter) as calcium carbonate is classified as soft; 61 to 120 mg/l as moderately hard; 121 to 180 mg/l as hard; and more than 180 mg/l as very hard”
- Soquel Creek Water District, "Water hardness" (1 grain per gallon = 17.1 mg/L). “One grain per gallon of hardness equals 17.1 mg/L”
- City of Ontario, Municipal Utilities Company (domestic water supply). “Ontario Municipal Utilities Company (OMUC) provides safe, efficient, and economical production, transmission and distribution of the City's domestic water supply”
- California Water Boards CCR, City of Ontario 2025 (PWS CA3610034). “Hardness as CaCO₃ (Total) ppm NA NA [3] Average Range 124 82 to 150 91 85 to 99”
- City of Upland, 2025 Consumer Confidence Report. “(ppm) 2025 120 ND–340”
- Monte Vista Water District, 2025 Annual Water Quality Report. “Hardness (CaCO3) (Total Hardness) ppm N/A 90.8 - 340 135”
- City of Chino, 2025 Water Quality Report. “Hardness, T otal [as CaCO3] (ppm) 2025 248 230–260 1487 100–1907 90.8 84.5–99.1”
- City of Chino Hills, 2025 Water Quality Consumer Confidence Report. “range n/a 100-190 91-210 average n/a 148 101”
- Cucamonga Valley Water District, 2025 Water Quality Report. “hardness (as CaCO3) ppm n/a 109 - 142 125.50”
- Fontana Water Company, 2025 Consumer Confidence Report (CPUC copy). “hardness (caco3) ppm ns ns 97.80 - 187.00 151.35”
- Fontana Water Company, 2025 Consumer Confidence Report (CPUC copy). “Hardness (CaCO3) ppm NS NS 106.00 - 162.00 134”
- Rialto Water Services, 2025 Consumer Confidence Report. “Hardness mg/L N/A Range 130-220... Average 160 260”
- Golden State Water Company, Claremont water quality report (2025). “hardness [as caco3] (mg/l) n/a n/a 97 - 330 190”
- City of La Verne, 2025 Water Quality Report. “Hardness, T otal [as CaCO3] (ppm) 2025 351.7 290–450 97”
- City of Pomona, Annual Water Quality Report 2024 (water tested 2023), Internet Archive copy. “Hardness (as CaCO3) ppm 160-360/260”
- Golden State Water Company, San Dimas water quality report (2025). “hardness [as CaCO3] (mg/L) n/a n/a 85 - 307 205 2025”
- City of Glendora, 2025 Consumer Confidence Report. “Hardness as CaCO3 (mg/l) NA NA NA 190 120 - 370”
- City of Covina, 2025 Consumer Confidence Report. “Hardness as CaCO3 (mg/L) NA NA 2025 230 190 - 280”
- Walnut Valley Water District, 2025 Consumer Confidence Report. “Hardness, Total [as CaCO3] (ppm) NA NA 234 189 - 280 97”
- Walnut Valley Water District, 2025 Consumer Confidence Report. “Hardness, Total [as CaCO3] (ppm) NA NA 215 190 - 270”
- Jurupa Community Services District, 2025 Water Quality Report. “Total Hardness (CaCO3) (mg/L) NA NA 162 25-220”
- Rubidoux Community Services District, CY 2025 Consumer Confidence Report. “Hardness, T otal [as CaCO3] (ppm) 2025 273 210–340”
- California Water Boards CCR, City of Norco 2025 (PWS CA3310025). “50 - 220180 - 21054 - 19054 - 19050 - 220130.6”
- City of Corona Department of Water and Power, Consumer Confidence Report. “Range 82 - 94 279 - 298 290 - 570 7.2 - 290 Average 88 288 452 146”
- Suburban Water Systems, San Jose Hills 2024 Consumer Confidence Report (latest found). “Hardness, totaln/a 2024ppm CaCO3187.576-303214.9160-274.4”
- WeatherSpark, Average weather in Ontario, California (modeled; rainless period April 22 to October 20). “The rainless period of the year lasts for 5.9 months, from April 22 to October 20”
- Viracon, Glass Cleaning and Maintenance Recommendations (mild non-abrasive cleaners; no razor blades; wet concrete slurry etches glass). “extremely alkaline and will eventually etch the glass surface”
- Viracon, Glass Cleaning and Maintenance Recommendations (mild non-abrasive cleaners; no razor blades; wet concrete slurry etches glass). “a soft, clean, grit-free cloth and a mild, non-abrasive, non-alkaline cleaning solution”
- Glass Doctor, "How to remove water spots from windows" (sprinkler minerals; vinegar mix; etching; prevention). “spray the glass with a solution of equal parts water and white distilled vinegar”
- Viracon, Glass Cleaning and Maintenance Recommendations (mild non-abrasive cleaners; no razor blades; wet concrete slurry etches glass). “can scratch glass surfaces and should not be used to clean glass”
- Glass Doctor, "How to remove water spots from windows" (sprinkler minerals; vinegar mix; etching; prevention). “glass is permanently damaged from hard water spots and glass replacement is your only option”
- Unger, "Window cleaning with pure water" (March 25, 2021). “safely from the floor and without drying and polishing”
- Glass Doctor, "How to remove water spots from windows" (sprinkler minerals; vinegar mix; etching; prevention). “hydrophobic coatings create a protective barrier that repels water”
- Housecall Pro, "How to price window cleaning" (hard-water stain removal as an extra line). Updated October 12, 2026. “extras like screens, tracks, or hard-water stain removal run $2-$30 each”
Written by Foothill Home Services. Local prices on this page are our own draft rates from the price list the quote tool uses. Where we quote an outside page, the quote is linked in the sources above, and we last checked this page on October 13, 2026. Other outside figures are described as the source reports them.
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