Let's not freak out too fast here, water spots will occur to all of us on a regular basis unless your car doesn't see rain. The likelihood that hard water spots form if you are using the paint sealant is next to none assuming that we talking regular condition here.
I found that the main cause of hard water spots is acid rain and hard water at your house. Your regular rain won't qualify in my mind and you are overthinking this. Wash the car as normal and let us know, at its worst you may need to clay bar it but i've never ran into that myself just because of rain and hot weather....