A1 hardwater stain remover...it isn't cheap, but it works.

https://www.amazon.com/1-Hardwater-Stain-Remover-Gallon/dp/B077Y63XG3

did you try window cleaner? There is a product called Invisible Glass....made to get the built up road salts etc off of car windows....used by those of us who live where they periodically salt the roads. Bet that would work.

I love this stuff. I use it on everything with hard water spots. I discovered it on my own, then found out my window washer uses it on my windows, too. I think you can buy it at Ace Hardware or online...

https://www.bio-cleanproducts.com/product/a-48-oz-jar-of-hard-water-stain-remover/

Thanks for the suggestions! Linda, reading some reviews about your suggestion has got me thinking a little about how people use toothpaste to shine up their headlight covers. I will look for this product and also try if toothpaste has the needed abrasion. Olychich, I'll look for it. It's kind of pricey if it doesn't work ($50; or maybe I can find a smaller size?)

lily, I got a free sample at Ace Hardware, which is how I discovered it. I think the company will send you a free sample, too. Ace probably has smaller sizes, if there is one near you. I just ordered online several years ago and the tubs last forever and it works!

Angels singing! Olychick - I tried that stuff and OMG! Awesome! It still took me several hours to do 11 windows (I probably should have gotten a bunch of new scour pads, but was a little afraid of scuffing the windows - next time), but at least the hard water budged (nothing else moved the needle any bit). Thanks SO MUCH for the recommendation!!!

That is great! I feel the same way about the stuff. I cleaned the water spots off of all my really expensive shower fixtures that look like metal but are really plastic, when nothing else did (cleaned the metal bits, too) and a few other things that NOTHING works on. It's great on tile and grout, stainless sinks, etc.

Where did you buy it? I recommend it so much that I'd like to know where it's available besides ACE if you didn't get it there.

I got it at Ace. It was a smaller bottle (I don't have it here as I left it at the rental house), i'm thinking maybe 8 oz? It was $12. I think I probably used only about 1/3 of it. Amazon has it (where I was reading the reviews), but then you'd have to wait for shipping.

I have been looking for such a bio window cleaner for a long time, thank you for your suggestion! Actually, I have health issues and toxic cleaning products negatively affect my health, so if I use them, my body is covered with red spots. So, I have been using natural cleaning products for several months and I feel great. As you know, some natural products cannot remove tough stains or rust, so I'm looking for a universal product that will cope with this. I hope the bio window cleaner works great. Anyway, if I want to do general cleaning, I hire a cleaning company that helps me clean the windows inside and outside the house. I have 2 large windows that I can't wash, so I'm very grateful to the staff of the cleaning company for their help. By the way, if you are nearby and looking for professional window cleaners, then you can visit this website to learn more about the best window cleaning service in that area.