When I moved out of my apartment, I had a heck of a time cleaning the shower doors. They were glass, and had hard water deposits on them. I tried all kinds of methods, from tree-hugger ideas, to the harshest chemicals I could find. Nothing worked.
As I’ve showered in my new place, I’ve noticed the water spigot and handle have some light deposits on them. Rather than wait until they become bad and then be stuck without a remedy, I’ve decided to do a preemptive action. After each shower, I wipe the spigot and handle with a towel. I also wipe the glass tiles on the wall. It will keep new deposits from forming, and I think the repeated wiping is wearing off the old deposits that have already started.