I don't get water spots if I'm diligent with my process. I only wash after the sun puts its shadow over the driveway (east facing). I also re-foam the panels until I have finished the contact wash for all panels. Or I'm doing a rinseless wash, which is done one section at a time and will never spot.
I've also been working on a hybrid wash process. Do a foam pre-wash when necessary, then rinse, but finish with rinseless after pulling the car into the garage. It eliminates the 2nd foaming, the 2nd rinse, and laundering of the wash mitts/pads. You just go straight into drying with a twist loop when you're done with the sponge on each panel.