How to remove hard water stains from windows (and when to call a pro)

Iowa tap water is hard, about 12–18 grains per gallon in most of the Des Moines metro. When sprinklers spray windows, that mineral content dries into white, chalky spots that won't come off with normal cleaner.

What hard water stains actually are

Calcium and magnesium left behind when water evaporates. The longer they sit, the more they bond to the glass and even etch the surface.

What works

• Distilled white vinegar (50/50 with water) for fresh, light stains (less than a few months old)
• Specialized hard-water removers (Bio-Clean, CR Spotless) for moderate stains
• Cerium oxide polish for severe stains, this is what auto detailers use on windshields

What doesn't work

• Razor blades on tempered glass, they leave micro-scratches that catch light forever
• Standard window cleaner alone
• Magic Eraser (works on porcelain, scratches glass)

When to call a pro

If the stains have been there more than a year, or if the glass feels rough when you run a fingernail across it, you're past the point of regular cleaning, you need restoration. We can usually quote restoration work next-day and will tell you honestly whether it's worth doing versus replacing the pane.

Prevention

• Re-aim sprinklers so they don't hit glass at all
• Squeegee water off windows after pressure washing siding
• Get a sprinkler head with a flow stopper if you can't move the head