We were chatting on another thread and I have been meaning to bring up a product that I have used with awesome success.
I have never had issues with my own boat cause we are anal about it and wipe it down all the time, but I have bought and sold a few boats from auction or other people and I have seen the stubborn water spots.
This stuff works for real. I have tried all the other stuff people recommend on here, but this stuff really works. Simply follow the directions and wear gloves and yes there is still some serious elbow grease needed, but it works.
I have done two totally covered boats and it works great. This is the stuff that auto dealers, detailers and boat dealers use.... They have other awesome products as well.
it is the waterspot remover #600