The stuff I use is Aspen Sani-Chips which allows me to bury the bowls halfway into the substrate which seems to work out, though sometimes they'll play around in their water bowls when they drink and splash it around but that's why it's awesome, because the Sani-Chips trap the water at the source instead of leaking it all through the substrate. AND, the snakes only displace enough water to just bump their humidity a pinch most of the time so it actually acts as somewhat of a lazy humidifier (at least that's how it works in my setup; maybe I'm lucky).