Most likely the water spots aren't from rain, morning dew or anyother type of "natural" source. Most likely hard water from car wash, sprinkler, etc.
I had the same problem with my daily-driven Grand Prix, when I bought it from a dealer's lot a couple years ago.
I polished the water spots out, (needed polishing anyway!) Then added a couple coats of Z2P. (BFWD now.) That would be my recommendation.
The worst water spots I've seen were created on a day when it was 100 degrees, black car in a supermarket parking lot, and the dang sprinkler system came on!!! :cursing::banghead: Those spots were PERMANENTLY FRIED into the paint surface. Never got them out.:doh: (My previous vehicle!)