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Those spots are hard water scale, not dirt. Sprinkler overspray lands on the glass, the sun evaporates the water, and the dissolved calcium and magnesium stay behind and bond to the surface. Ordinary glass cleaner contains nothing that dissolves mineral deposit, which is why scrubbing does not work. It comes off with an acidic mineral restoration pass. Left for years it etches the glass permanently, and at that point no cleaner will fix it.
Last reviewed 3 September 2026 by Perfect Shine Home Solutions, Kuna, Idaho. Serving the Treasure Valley since 2016.
Water hardness varies a lot across the valley. Meridian is published at roughly 8.4 grains per gallon and Garden City at around 10.0, while Boise sits near 6.6 and Nampa is comparatively soft at about 3.5. The harder the water, the more mineral is left behind by each drop that dries on your glass. That is why the cloudy-lower-panes complaint is a Meridian and Garden City signature and much rarer in Nampa.
Look at where the spots are. If they are concentrated on the bottom two or three feet of the glass and the top is clear, that is irrigation overspray, not weather. Subdivision sprinklers run before dawn, clip the base of the windows, and the sun dries them by mid-morning, every single day through the watering season.
A restoration pass: a mild acidic mineral remover worked across the affected glass, then fully neutralised and rinsed. It is a different job from a wash, it takes considerably longer, and it is quoted separately for that reason. Some products sold for this are aggressive enough to damage frames and landscaping if used carelessly, which is the main argument for not experimenting on your own windows.
Mineral scale sitting on glass will, over a period of years, etch into the silica surface. Etched glass is physically pitted, not coated. Nothing cleans it back to clear, and the only remedy is replacing the pane. This is the reason to deal with it in year one or two rather than year six.
Adjust the sprinkler heads so they do not hit the house. That one change does more than any cleaning schedule. If a head genuinely cannot be redirected, cleaning the glass twice a year keeps the deposit from ever getting thick enough to bond hard.
| City | Grains per gallon | Parts per million |
|---|---|---|
| Garden City | 10.0 | 170 |
| Meridian | 8.4 | 143 |
| Boise | 6.6 | 113 |
| Nampa | 3.5 | 61 |
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On light, recent spotting, sometimes. On bonded scale that has been building over a season or more, no. Vinegar is weak enough that it needs long dwell times, and long dwell times on glass in the sun cause their own problems. It is worth one try on fresh spotting and not worth your Saturday on anything older.
It can be. Scale left on glass for years etches into the surface, which is physical pitting rather than a deposit. Once that happens it cannot be cleaned off by any method, and the pane has to be replaced. Fresh and moderate scale comes off cleanly.
Of the cities that publish a figure, Garden City is hardest at around 10.0 grains per gallon, then Meridian at about 8.4, then Boise at about 6.6. Nampa is the softest of the four at roughly 3.5.
It is quoted separately from a standard window clean because the labour varies enormously with how long the scale has been building. We look at the glass first and tell you whether it will come off before we quote it.
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