I can attest to Koch Chemie FSE being an easy and amazing product for water stains. Just incredible. John on Forensic Detail Channel used it slightly off label, and man does it work great.
Try a water spot remover and if that doesn't help then it needs to be polished out.
I'd go over the paint with a water spot remover anyways since if it doesn't remove the water spot entirely, it helps begin to break down the minerals that cause the spotting and they will be polished out easier. Or at least that's the theory behind it
Typically it's acid that can take out water spots.
Check out Car Pro's Descale. It's a soap that's very acidic used to refresh ceramic coatings but also can be used for cars to take out water spots. If this spots are fresh, I would think this would work pretty well. Hopefully the sun didn't bake it in too bad...