There's a few things you can try for water spots on glass. First, start out with a good glass cleaner. I use 409 Glass and Surface. If that won't work, try a diluted mixture of vinegar and water (2 parts water to 1 part vinegar). Windex also makes a pre-diluted vinegar solution if you want to give that a try. A similar mixture of Simple Green and water may work if you need something a little stronger.

If these suggestions don't work, you can (as a last resort) use steel wool. Make sure you get the finest gauge you can find. I will caution you that I've never tried this and don't recommend it unless it's absolutely necessary. I've read of other people using steel wool with good results, but keep in mind that there is the possibility that you can scratch the glass. Use with caution.