How to remove hard-water spots without scratching the glass

Most hard-water damage to windows is done by the cleaning, not the water. A razor blade that “just takes the spots off” can leave scratches that are there for good, and on coated glass it can strip the coating. Here is what the people who make the windows say.

What the window makers say

• Andersen: a solution of equal parts vinegar and water; no razor blades or abrasives; do not pressure wash.
• Pella: never use a razor blade; use a vinegar-based cleaner without ammonia or alcohol.
• Marvin: no scrapers of any kind, and glass scratched by a scraper is not covered under its warranty; no pressure washer.
• Milgard: never use razor blades, putty knives or abrasive pads, especially on glass with a low-E coating on the room side; no harsh chemicals or high-pressure hoses.

The glass industry’s own cleaning standard treats a razor blade as the last possible option on heat-treated glass, and never the right tool for a coated surface.

A safe order to try

1. Rinse first. Wet the glass to float off loose grit. Rubbing dry dust across glass is how scratches start.
2. Equal parts white vinegar and water on a soft cloth. Let it sit on the spots for a minute or two, wipe, rinse with clean water, and dry the glass.
3. Repeat on the stubborn ones. Mineral builds up in layers and comes off the same way.
4. Stop if it will not shift. Stronger products exist, but on coated or tempered glass they are a job for someone who knows what the glass is.

When a spot will not come off

If the glass is clean and dry and still looks cloudy, the surface itself may be damaged. At that point there is nothing sitting on top to remove, and no cleaning will bring it back. Vitro notes that glass kept clean and dry resists this kind of damage, which is the best argument for dealing with spots early.

Stop it at the source

Turn the sprinkler so it misses the glass. Hard water in the Gallatin Valley explains why even city water spots windows.