I have used a small tub of room temp and one heated to 75-82 degrees. They always prefer the heated water. I use titanium aquarium heaters since they are less likely to brake. Make sure that you protect them with a guard so that the lizard doesn't lay on it and burn him, it will scar them or hurt them at least. Niether of which is good. This is great for the water monitors, plus they deficate in the water and it is easily washed out.