What's the best way to remove water stains from glass shower doors/walls?

Mix vinegar and water and sponge it on. Leave it on maybe five minutes then use a mild abrasive like a plastic scrubbee to take it off. When removing it you can mix all-purpose cleaner to help. Rinse very well afterward, as the acid could continue to work.

Really thick encrustation could take repeated applications, or longer soaks, but will work eventually. Just don't scratch the glass as that is permanent. By the way this answer applies for limestone or white mineral stains; if it's red rust, buy Whink as it works in a jiffy.

Those mineral deposits come away easily with spray-on products and a small amount of elbow grease. Scrubbing Bubbles and Kaboom bathroom cleaners both do the job.

You may be able to remove them more cheaply with white vinegar, but it has quite the smell and runs down the glass, so it can't soak off the deposits even briefly.

I use paint thinner in my rental units. It works quickly, but the bath will need to be left open for a few days to disperse the odor of the paint thinner.

There is a product called Showerlux door cleaner its brilliant !! One bottle goes along way. here is a link.

http://www.waltonbathrooms.co.uk/viewlevel.aspx?ma...

Purchase a bottle of "CLR" It removes "C"alcium, "L"ime and "R"ust. Excellent product!!!