Toothpaste does a great job when cleaning teeth and isn't too abrasive, so it may do a great job of removing hard water glass stains as well -- without harming the surface underneath. Read more ...

Q: Is there any way to remove hard water spots from a glass shower door? A: When glass doors are left to dry on their own after showers, the water evaporates but minerals stay behind. Gradually ...

When glass is washed with hard water ... could use either a commercially made product or a homemade one to remove hard water stains. For a homemade solution, you will need distilled white vinegar.