Household white vinegar will work on the water spots as long as they're not toooooo old. It's worked for me. You can try claybar, too. I found that if the vinegar didn't work, neither did claying it. YMMV of course.
3M SMR is a good alternative if neither of those "non abrasive" techniques works.
accmdx's issue is going to be different, b/c he hasn't had the TSB done, so the water is always going to be in the same place, and is always going to "stain" in the same trickling location. Before I had the TSB done, the vinegar reduced -- but did not eliminate -- the streak/spot/trail under the mirrors...because the weeping was too continuous and in the same spot. 3M took it out.
You don't want to 3M SMR on a regular basis, especially in the same place.