How to clean water deposit spots off windows

White spots and hazy rings on glass are one of the most common complaints about windows, especially on panes that catch the garden sprinkler or the runoff from a roof. They come from the minerals in water. Deal with them early and they come off easily. Leave them for months and they can etch into the glass for good.

Why the spots appear

Tap water and borehole water carry dissolved minerals, mainly calcium and magnesium. When a drop dries on the glass, the water evaporates and the minerals stay behind as a white, chalky mark. Each time the glass gets wet and dries again, another thin layer builds up. Windows near sprinklers, pools and overflowing gutters collect spots fastest.

Why they etch over time

Fresh mineral spots sit on top of the glass. Over time, especially in strong sun, the deposits react with the surface of the glass itself and slowly roughen it. At that point the spot is no longer a deposit that can be wiped away but a mark in the glass, and cleaning will only improve it so far. That is why it pays to clean spots off while they are still fresh.

The vinegar method, step by step

White vinegar is a mild acid that dissolves mineral deposits without harming ordinary glass.

1. Rinse first. Wipe or rinse the glass with clean water to remove loose dust and grit, so you are not rubbing sand across the surface.
2. Mix the solution. Mix equal parts of white vinegar and warm water in a spray bottle. For heavy build-up, use the vinegar undiluted.
3. Spray and wait. Spray the spots generously and leave the solution to work for five to ten minutes. Do not let it dry; spray again if it starts to.
4. Wipe gently. Wipe with a soft cloth or a non-scratch sponge, working in small circles over the spots.
5. Soak stubborn patches. Soak a cloth in the solution and hold it against the worst patches for a few more minutes, then wipe again.
6. Rinse and dry. Rinse with clean water and dry straight away with a lint-free cloth or a squeegee, so new drops do not dry on the glass and start the cycle again.

Work on one pane at a time, and avoid cleaning in direct, hot sun, where the solution dries before it has done its job.

What not to use

• Abrasive powders and scouring pads. They scratch the glass, and the scratches hold dirt and catch the light.
• Steel wool and razor blades on coated glass. Many modern windows have a coating on one face, such as a low-e or solar control coating. Scraping or scouring can damage a coating permanently.
• Strong acids and harsh chemicals. They can damage coatings, frames, rubber seals, and the paint and plants around the window.
• Cleaning in hot sun. The cleaner dries too quickly and leaves streaks of its own.

If you are not sure whether a window has a coating, treat it as if it does and stick to vinegar, water and a soft cloth. Our guide to low-e glass explains a quick way to check.

Keeping the spots away

• Point sprinklers away from windows and glass doors, or water at times when the glass will not dry in hot sun.
• Keep gutters clear so water does not overflow and run down the glass.
• Dry wet glass with a squeegee after heavy watering or washing the car nearby.
• Clean windows regularly, so deposits never get the chance to build up and etch.

When the glass is past cleaning

If spots have etched deep into the glass, no cleaner will remove them completely, and a badly marked pane can make a room look permanently dull. At that point replacing the pane is the practical answer. Our window glass replacement page explains how it is done, and you can request a free quote with a photo of the marked glass.