To be honest, I've never seen any conclusive testing that proved that an all man-made, or synthetic paint sealant protected paint from water etchings better than what most people consider a traditional Carnauba wax, (paste or liquid).
Follow me on this logic...
If water drops are landing on your car's paint and there's something in the water corrosive enough to etch a spot or hole into a modern urethane clear coat finish... then chances are very good it's going to have no problem getting past the micron thin layer of protection you apply by pouring out of a bottle or scooping out of can.
Does that make sense?
Try not to park your car where sprinklers go off, I've witnessed some pretty bad water etching spots from city water sources.
Also, just to note, there's two types of water spots, Type I and Type II
Type I = Mineral deposit on the surface
Type II = Etching or hole in the actual clear layer of paint
Type I can be removed by washing, claying and in some cases a paint cleaner is needed to remove any type of surface mark. In some cases you could also use vinegar or a commercially available decontamination system.
Keep in mind there is acid rain spots, alkaline rain spots and whatever is in the city water or your well water.
Type I must be removed by using an abrasive product to remove paint surrounding the etching to level or flatten out the surface.
