The spots are on the outside from a lawn sprinkler. Same method?

Yes — that is mineral scale from hard water drying on the glass. Vinegar still dissolves it. Work in the shade so the cloths stay wet, and keep acid off a stone sill under the window.

Is vinegar safe on Low-E or tinted window glass?

Vinegar on the glass face is the usual household method. The risk is mechanical: do not scrape Low-E or film with a metal razor, and do not let acid run under the edge of a film.

Guide

How to Remove Hard Water Stains from Windows

Wet the glass with distilled white vinegar, let it sit 10–15 minutes so the minerals loosen, wipe or squeegee, and dry the pane. Keep acid off stone sills and painted wood. Do not mix vinegar with bleach.

Windows Hard water buildup

Context

Conditions that change the method

Delicate surface — Keep vinegar off marble or limestone sills and off painted wood trim. Do not use a metal blade on Low-E or tinted film.

Do not mix vinegar with bleach

Never mix vinegar with chlorine bleach or an unknown window cleaner that may contain bleach — that combination produces toxic chlorine gas. If vinegar splashes in your eyes, rinse with running water and get medical care if discomfort continues.

What you need

Distilled white vinegar
A spray bottle or soaking cloths
Microfiber cloths or a squeegee
Clean water for a final wipe

Dust the pane so grit will not scratch the glass. The spots you want are cloudy white or tan mineral dots, often on the outside where a sprinkler hits the window.
Spray or wipe undiluted distilled white vinegar over the stained glass until the surface stays wet.
Let the vinegar sit 10 to 15 minutes. On heavy outdoor scale, lay vinegar-soaked cloths against the glass so the acid does not dry in the sun.
Wipe or squeegee the loosened minerals. Repeat the soak on any island that is still rough to the touch.
Wipe the glass with a clean damp cloth to remove leftover acid, then dry the pane and the frame edges so drips do not leave a new ring.

What to avoid

Do not let vinegar pool on stone sills or soak into painted wood trim.
Do not scrape Low-E or film-coated glass with a metal razor.
Do not use abrasive powder on the pane — it frosts the glass and the spots look worse.

Products

What to use

Related guides

FAQ

Questions people ask

The spots are on the outside from a lawn sprinkler. Same method?: Yes — that is mineral scale from hard water drying on the glass. Vinegar still dissolves it. Work in the shade so the cloths stay wet, and keep acid off a stone sill under the window.
Is vinegar safe on Low-E or tinted window glass?: Vinegar on the glass face is the usual household method. The risk is mechanical: do not scrape Low-E or film with a metal razor, and do not let acid run under the edge of a film.

Sources

Hardness of Water — U.S. Geological Survey
Cleaning Tips & Advice — American Cleaning Institute