Good Afternoon,
Removal of Hard Water Spots from paint can be tricky. One method is to try using claybar on the area to see if that removes the mineral contaminants (water spots). Another method is to use some sort of correcting polish and a machine. Something like Adam's Swirl and Haze Remover on the Flex 3401VRG Polisher or Porter Cable 7424 should kill whatever spots aren't into your clear coat. If they are a little deeper, you would need to use something like Adam's 4" Focus Kit. It's a polishing kit that you use on a Cordless Drill. From there, it would be key to come back over it with a Dual Action Machine, to remove the tiny buffer trails the Drill left.
The pic below is something I hit at a show over the summer. I spent all of about 10 minutes on the good side of the hood. Clay, Swirl and Haze Remover, and Fine Machine Polish.
