Okay, I promised to share this tip. Hard water stains are hard to remove from shower doors, windows and kitchen and bath faucets. Here is how I remove hard water deposits in my home. Take white vinegar and a scrubber sponge. For shower doors and faucets I soak the scrubber side good and start scrubbing. This works very well for me. I then just rinse with a damp cloth and dry.
Look at my faucet I did today. 12 years old and not any deposits. I do have to scrub up around the handle too to get those off but I sometimes soak a wash cloth with vinegar and wrap around to work on those hard water deposits.
To clean outdoor windows and remove hard water stains I do it a little different. I take a bowl and add 1 cup of vinegar, a small squirt of dish soap and some hot water. Using the same scrubber side of the sponge I work at the hard water deposits and then use the sponge side to scrub the whole window and squeegee them dry. If you have stubborn water stains then soak that scrubber with straight vinegar and scrub really well.