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 ...

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.