Just throwing this out there as a possible culprit-
No paint will adhere well if any of the cleaning agents (Dawn, degreaser, Simple Green, whatever one is using) are left on the surface. I've taken to doing several rinses, with a soft toothbrush. Another possibility is calcium in the water. If your water leaves a film when it dries, that film may be the issue (even if you can't see it). I usually do a final rinse with alcohol to be sure any foreign matter is removed.