How to Remove Hard Water Spots From Windows

Those white, cloudy spots that won’t wipe off are minerals. Water carries dissolved calcium and magnesium, and when a drop dries on glass the water goes and the minerals stay. A normal window cleaning takes off dust and grime but doesn’t dissolve a mineral crust, so the spots can survive a good cleaning and look exactly the same the next morning.

Where the spots come from

Look at the sprinklers first. One head turned a few degrees off will spray the lower panes every morning, and by August there’s a frosted band across the bottom of the window that stops right at the height of the spray. Run the system, watch where the water lands, and adjust the heads before you clean anything. Otherwise you’ll be dealing with the same spots again in a couple of weeks.

Up in the foothills the other usual source is well water. Plenty of homes in Evergreen, Conifer and Bailey run on private wells, and mineral content varies from one well to the next, so two houses on the same road can have very different spot problems. Hosing off a deck or washing the car near the glass leaves the same marks.

The dry air makes both worse. Water evaporates fast on the Front Range, so a drop has less time to run off before it dries in place, and strong sun on the glass speeds that up.

Removing fresh spots

Spots that have been there a few weeks usually come off with a mild acid and a bit of patience.

1. Wash the window first with soapy water and a squeegee, so you’re working on the minerals and not the dirt sitting on top of them.
2. Mix white vinegar and water about half and half in a spray bottle.
3. Work in the shade, or do that side of the house early or late in the day. Vinegar that dries on hot glass leaves its own film.
4. Spray the spotted area and leave it for a few minutes. Keep it wet, and spray again if it starts to dry.
5. Wipe with a microfiber cloth or a non-scratch pad, using light pressure.
6. Rinse with clean water, then squeegee or dry the glass.

Faint spots may need a second or third round. For heavier deposits there are hard water removers made for glass. Read the label, test a corner first, and keep acids off window frames, painted trim and stone sills, which they can mark.

What not to use

Steel wool and abrasive scouring pads leave fine scratches. Most modern windows also have a low-E coating, and scrubbing hard at a coated pane can damage it. Abrasive powders are out for the same reason.

Go carefully with razor blades. A blade is a normal tool for paint specks and old stickers, but tempered glass (required in doors, low panes near the floor and beside tubs) can have tiny particles fused to its surface during manufacturing. A blade can catch one and drag a scratch across the pane. Tempered glass usually has a small stamp etched in one corner. If you can’t find one and aren’t sure, leave the blade out of it.

When the spots won’t come off

If you’ve done all of that and a spot is still there, the minerals have probably etched the glass. Deposits left for months or years slowly eat into the surface, and at that point there’s nothing sitting on the glass to remove. Sometimes you can feel it as a rough patch under a fingernail.

Etched glass can sometimes be improved with specialty polishing compounds, and badly etched panes get replaced. Neither of those is a cleaning job, and scrubbing harder won’t change the result.

Keeping them from coming back

Most of the fix is the sprinkler adjustment. After that, avoid rinsing windows with well water and letting them air dry, and deal with new spots while they’re still sitting on the surface. Glass that’s cleaned on a regular schedule also gives minerals less grime to cling to. How often that should be depends on your house.

If you’d rather have the windows done for you, we clean every pane by hand with a squeegee and chamois, inside and out, with the sills and screens included. Mention any spotted panes when you send the quote form so we know what we’re walking into.