I'm a fervent recommender of this product. This is copied from another recent post about hard water stains:

I'm going to look like a shill for this company because I posted this
same info on two other threads, but I really have no connection to them
other than being extremely pleased with their product. I was sick about
the water/mineral stains on a new sink as well as the metal and metal
look plastic on my Hansgrohe shower fixtures. I tried everything and
this stuff is a miracle. My window washer uses it to remove water spots,
too.

Try this...it's taken water spots off every single thing I've ever
tried it on, it's non toxic, non abrasive. You can sometimes get free
samples at Ace Hardware if there is one near you. There are other
products called Bio-Clean, be sure you get THIS one:
I have only used the cream in this container, can't vouch for the liquid.