Dave,
I also use distilled water, but I still have a small problem with it drying to fast on the tip. My needle is pretty small though. A .2mm on a iwata hp-B airbrush. So I also add a drop or so of Jo Sonja flow medium/airbrush medium. Then it airbrushes great. I may be the only one that has a slight problem, and that would be normal for my case. Good Luck.
Brad Spelts