As big as you can get. I have 3 in the Exo Terra 36 x 18 x 36, and you're looking for as tall as you can find. I would not go any small than a 24 inch high since their natural instinct is to be high. And letting them use their natural instincts makes for a happy healthy frog. Can't help you with the water issues since I'm to paranoid using something like that.