If you are washing outside then drying inside the water spots must have been there prior to washing, i.e. they are etched on. They will continue to reappear no matter how much you wash the car.
You can try a few things:
- Some people have claimed they had luck with their clay bar removing them. I think it will work if the hard water etching isn't too bad.
- You can purchase a bottle of chemical guys hard water spot remover. I don't have a link to it handy, but I know it's out there (I have a bottle of it). It works pretty well, but requires a fair amount of elbow grease to do the job.
- Lastly, you can use a light polish with a finishing pad to polish out the spots on the panel. I had them on my CF room and they wouldn't completely come off with the chemical guys stuff, so I used their scratch and swirl be-gone with a finishing pad, then used jetseal to seal the roof. Spots are completely gone.
Once they are gone for good, you need to prevent them from forming. The key is to dry the car immediately after washing it. Don't allow the water to sit and pool on the paint at all. It's tough, but it works and it beats paying money for a hard water filter system for your garden hose. Since I've polished mine out, I just dry it quickly and don't let the air dry it. No more water spots here.
'11 BMW E92 ///M3 - ZCP and DCT
'15 Ford F-250 - Lariat, 6.7 Powerstroke Turbo-diesel