Prepare a paste of vinegar and baking soda. Apply the paste to the hard water stains. Leave the paste for 15 minutes. Then scrub using a soft scrubbing sponge or soft bristle toothbrush in a circular motion.
Wipe off the paste with a damp cloth.
If the stain persists, spray a mixture of vinegar and water on the glass and wipe off with microfibre duster or folded newspaper.
Alternatively cut the lemon in half and rub it directly on the stain. The acidity in the lemon will remove hard water deposits. Wipe off with a microfibre duster.
Note: Incase you have marble flooring in your bathroom, please be careful when using lime or vinegar as both are acidic and can etch the marble. Place a cloth at the bottom of the glass shower cabin so no lime or vinegar falls on the marble.