The ultrasonic fogger keeps the water warm and the 'fog' humidifies the air. Some of the iguanas lick the water drops that form on the side of the soaking trays (in this case, a ferret litter pan). My larger iguanas have jumbo sized cat litter boxes and the fog occassionally gets so dense that you can't see them. I purchased two foggers through a pet store and then realized that it's the same thing as foggers sold by pond supply stores. (Some come with a coil which I take off anyway) I get them from a discount pond supply store as they sell for about $35 less. It's amazng how marking an item *Reptile* or *Pet* makes the price skyrocket.