Quote Originally Posted by Tainted Glory
I had an issue with humidity in my RBI rack as well. I remedied the problem by drilling a total of ten holes in each tub (8 along the front and 2 on the sides, toward the front). I now only fill my water dishes half way and keep them on the cool side. A combination of these things has stabilized my humidity to where I like it.

I'm using newspaper substrate btw,
Well, the depth of the water makes no difference whatsoever. Surface area is what impacts the evaporative coefficient, and thus the humidity. I've been working with various water dishes, and think I've got the right ones now. I also melted holes every 2" all the way around the upper lip of the tubs, so it's very well ventilated now. I'm using 2 different combinations of water bowls. One larger single bowl for my adult tubs, and 2 smaller bowls for the tubs I have dividers in. It's maintaining humidity in the 52-57% range right now, after 2 days.