Formula 4 Spray Wax. Is this the best way to prevent water spots? 

I would say that contrary to what marketing says, there is no hydrophobic product that will prevent water spotting. I'd say they increase water spotting. Most dishwasher rinse agents are actually hydrophilic and cause the water to sheet off completely. When you have a hydrophobic surface you end up concentrating some of the water that is left and leave the spots. Where the waxes do help is preventing the water spot from etching the clear. If you want to avoid water spots when you dry I would say DI rinse is the best way. Otherwise, a spray bottle made with distilled or DI water and a rinseless wash or waterless wash like Armour Adapt as a drying aid is about as good as you can get. This stuff will make the water spot easier to remove, but I don't think it can truly prevent water spotting for any water that remains on the surface.

I just got a gallon of it this past week. I have to try it to see if does helps with water spots with summer heat.