I have a boat and the lake waterspots are nasty especially when its over 100 degrees. I use soft water with a heavy dose of vinager and a little less of window cleaner concentrate. Micro fiber it on and use a dry one to wipe it off.
I also like Lucas Slick Mist Speed Wax to follow things up with for a final shine. It will get off the minor water spots. It may take 2-3 times with this solution but it has always worked in the past.
I make up a gallon of this at a time so it is always handy in a ruber maid container. good luck.