I would try white vinegar, spray it on there and let is sit awhile before scrubbing off.
vinegar mixed with water works miracles
If the vinegar isn’t getting it all, you could take a single edged razor blade and judiciously hold it at a low angle and scrape them.
I would try lemon essential oil
Vinegar usually works on my windows, we have very hard water! Try to let it sit, it's hard because it wants to run. I wet the window, then place paper towels on it and spray them down to try to keep the vinegar from just running off.
I agree that vinegar will probably do the trick! If you heat the vinegar for a few seconds in the microwave, that should help, too.
Try a little vinegar on a cloth along with a spot of w/up liquid too..
Here is a nice video tutorial for you: https://www.youtube.com/watch?v=saGAHGTSEug
Use a single edge razor blade, using a scraper attachment they sell in the hardware section at the big box stores. Everything including paint comes oft
Here's a post that might help - https://www.wikihow.com/Clean-Hard-Water-Spots-Off-Windows
Hey Polita: Try this:
Mix ½ water and ½ vinegar together and put into the spray bottle. Or, mix a paste in a small bowl made up of 1 part vinegar and 3 parts baking soda and put on a sponge and scrub. Or, you can pour lemon juice onto the scrub sponge and scrub in a circular motion until it starts to break down the hard water stains.
Or, check these sites:
It's for a shower door, but may work for you:
Believe it or not I used oven cleaner from the dollar store. It has ammonia in it and easy to spray. Then I just washed the windows down with a hose.
CLR would probably do the trick.