CLR (calcium lime rust) or Limeaway. You can get both at Wal-Mart in the cleaning products. It takes off water scale so easily!
A vinegar/water solution should work: https://home.howstuffworks.com/home-improvement/household-hints-tips/cleaning-organizing/shower-door-cleaning-soap-scum-and-hard-water-stains3.htm
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Calcium aka lime spots, clr for bathrooms, cleaning vinager. When you get the spots off, cooking spray, rainx when applied to doors acts as a repellent for the spots.
White wine vinegar left to soak.
A lemon cut in half and run the flesh over the stubborn arears. Again leave for a bit.
After leaving to work, go back wipe with a damp cloth then rinse. Should come back up good as new.