How can I remove hard water stains on my windows?

If it’s calcium something like CLR might work, or some other bathroom product. Pumice stone also might work, but you would have to test a spot to see if it scratches.

Vinegar should work. Put some in a spray bottle and cover the affected area. Leave on for ~15 minutes and then wipe off. Or, place some vinegar-soaked rags or paper towels and place them against the window.

If this doesn’t work, @JLeslie‘s suggestion of CLR should do the trick. I don’t recommend using a pumice stone though.

White vinegar is normally helpful in cleaning up lime deposits (which is what you get from “hard water”), but my question for you is “How are you getting ‘hard water’ stains on exterior windows?”

Hard water is water from a well, generally, which contains dissolved calcium compounds – and which municipal water systems mostly eliminate. Rain water won’t be mineral-laden (hard), because it’s formed from evaporation, which leaves minerals behind. If anything, you may have slightly acidic rain from the water’s interaction with volatile chemicals in the atmosphere, but that’s the opposite of hard water.

So… I’d also recommend Mr. Clean “Magic Eraser” cleaning pads, if you’re in the US. They’re available at supermarkets and home improvement stores, and work amazingly well. They’re all that I use nowadays to clean my tub, tile walls and sliding glass doors – which accumulate soap scum that’s otherwise difficult to clean. And they don’t scratch or abrade, either.

I am flabbergasted at the lack of DIY how-to’s on this matter. I have some very hard water where I live and am constantly battling hard water stains on our glass shower doors and walls and vinegar solutions and even CLR just doesn’t always cut it. I did find this one site that wants to sell me their magic solution that miraculously transforms stained windows to new condition and checking the MSDS sheet I find it is simply a low percent hydrochloric and hydrofluoric acid mixture in water. Less than 3% each. May just test this out on the shower.

I did read on some car restoration web sites that once the glass is clean to seal it by polishing it with a glass polish will help from the stains from coming back.

I agree with @CWOTUS. A solution of vinegar and water would work fine.You can also use barkeeper’s friend,mix it with little water and clean it using the green scrubby side of a dish sponge, follow up with glass cleaner.

You know the crud on the outside windows is really caused by acid rain and pollutants.

I use to clean windows in college, we used Spic & Span ¼ cup in a gallon of water and add ½ cup of Ammonia. Put it on with a sponge and scrape all the windows with a a single edged razor. Squeegee to remove liquid, towel dry.

1 part warm water + 1 part vinegar + newspaper.
Mix the liquids, spray on window, then wipe dry with a newspaper. I don’t know why it works. A window cleaner showed me this process and I’ve never forgotten it. Cleanest windows I ever had.

@CWOTUS Good question about how did I get hard water stains on the exterior surface of my windows if they only get rainwater on them. Maybe I have to rethink this. Maybe I was wrong. But this is what I’m looking at:

I have windows that you slide horizontally to open/close. One side is a fixed window that doesn’t slide. There is a screen in front of the side that slides. It’s only the window behind the screen that is affected. The bottom 2 inches of these windows look frosted. The stuff does not come off with plain soap and water. So I thought this was caused by hard water. For some reason, it’s only windows that have had a screen in front of them that have this problem.

Now, I think the windows have not been washed for > 25 years. Even if it’s just rainwater that falls on them, could this still be due to hard water accumulation?

A big “thank you” to all for your answers. I will try some of your suggestions, starting with the vinegar…

For people who battle water marks on shower doors and tiles, after you clean them really good, polish them with car polish. Do not polish the floor with wax.

The frosting on the windows sounds like some sort of mineral deposits, possibly precipitate from the metal screens. Most household cleaners are alkaline but hard water deposits require an acid cleaner. There are two products you might want to have a go with. ‘Lime-away’ and something called ‘Bar Keepers Friend’. Good luck. Let us know how it goes.

Household vinegar won’t cut it. It isn’t nearly acidic enough. Not for 25 plus years of mineral deposits.

@Cruiser – don’t even come near hydrofluoric acid! It can dissolve glass, but worse, it can absorb into your skin and dissolve your bones. see: http://en.wikipedia.org/wiki/Hydrofluoric_acid

I went around my house last month with a bottle of vinegar and a paper towel to get rid of hard water deposits. It took a few minutes, but everything came out shiny.

@RocketGuy I did point out it was less than 3% concentration in that formula…which brings it down to the PH of vinegar. No worries, but you are very right to point out the hazards of full strength Hydrochloric acid….nasty stuff.

If the glass is etched up from acid or dirt it will be a whole different story.

@Cruiser is right, @RocketGuy it is in the dilution. Even regular vinegar is only about a 5% to 8% acetic acid in water, with a pH of about 2.4. For my experiments and lab, I buy a stronger brand of vinegar. When we talk about cleaners, we deal mainly with solutions with a particular pH and they are ionic or non-ionic.

@2davidc8 If you have a jewellers loupe or decent magnifying glass you should be able to tell if the surface has deposits or is frosted because of degradation. Glass will cloud after being exposed to caustic chemicals. No amount of cleaning will fix that clouding. There are processes that buff out glass, if it really bothers you. Let us know.

@cazzie I don’t have access to a jewelers loupe, but I’ll try some of the suggestions given above, starting with the vinegar. I won’t have a chance to try anything until next week, though, but I’ll report on how things turned out. I also have a double-paned window that has failed (bad seal), so I’ll also try asking the window replacement person what he or she thinks of the frosted windows, which, as I said, has this hard deposit only on the bottom 2 inches of the windows.
Thank you for your answers.

Well, vinegar worked! Yay!!