By John Paterek Question I am the proud owner of a new 993 . It has metallic paint and came through without a mark on it. Recently, while under fluorescent light , I noticed water spot rings on the roof and sunroof panel. The spots you mentioned are mineral deposits from rain.
Acid rain is a pock mark deep in the surface usually from years of neglect.
I have removed this deposit by using 3M Imperial Hand Glaze and a small clean section of cotton towel. Polish by applying the glaze to the towel, buff in one general direction rubbing until the ring disappears. Again care must be used not to over buff at once. New Porsches need polishing and waxing to prevent this condition. The metallic base coat is now water-based with traditional baked enamel clear.