Yes, distiller water. I have used beads for four years and have never had a mold issue. I use 65% beads with the tubes from Heartfelt. I haven't been to the site in a long time and am only assuming that he still has them. About once every two of three weeks, I give my beads several "spritzes" from a soray bottle of distiller water. The bad thing about beads is that they tend to crack and you get "bead dust" in the bottom of your humidor. Not really an issue. As said, I've been using the same beads for four years and they are still intact for the most part.
Another thing, I used to stress do much about my humidity. Big time. You could probably search this forum and see where I have stressed about it. I have come to trust my beads so much, that the last time the batteries died on my hygrometers, I never changed them. I no longer use hygrometers.
DL