it's not necessary if you're going to use that heat light. I think your castelnaui will be more than happy with your setup as it looks nice and big and comfy. I have a pair of the amelanistic castelnaui, and I keep them in a 10 gallon, I try to keep it nice an humid in there as is recommended(spray everything down every day or every other day), and they are doing excellent as just got more eggs from my pair. If you are spraying them daily or about daily then you should scrap the water dish. It's just going to get filled with dead crickets, my castelnaui prefer to drink droplets of the glass or off a fake leafed plant I keep in there pretty much to spray down and its flat 'leaves' hold water nicely almost like a natural water bowl one could say. Hope this helps though...
