Is this just on the glass or on the paint as well?
A clay bar may not remove water spots. It is a good idea to clay the glass to start as this is the least aggressive method. If they are not removed then move to a polish. On
If the waterspots are on the paint and are etched into the paint a clay bar will not remove them. You need to use a polish and possibly a compound depending on what type of water spots you have.
This works really well. Just be sure to read the directions on the bottle. It is not safe to use on paint. Only on glass. The dye in the product will stain your applicator a bluish green. I would pick this up if it is only on the glass.