Here is my trick and I love it, I am not a expert detailer but my boats have always looked showroom new!!

Wash the boat with a car / boat wash product and rinse

wash the boat with "lime away" tub / shower cleaner, Only on the gel and glass

Wash the boat again with car / boat wash product

Wax with Meguires Flagship Premium Marine Wax.

The lime away takes off the pretty tough waterspots and doesn't seem to remove the wax. You'll be able to tell if it removes wax when you wash with soap for a second time.

The real key to keeping you boat waterspot free is to wipe it down after every time out. Honestly, the 5 minutes it takes to wipe it off saves hours of buffing and polishing.