Well, they're originally from the rainforest, so he's supposed to be in a hot, humid place. He actually absorbs the water through his skin, instead of drinking it! So he needs "rain" at least once a day in his terrarium.

[ She looked up from Pascal and beamed. He was the coolest pet, and no one could tell her otherwise. ]

I'm sorry! I didn't get you, did I? [ She just realized that Fi had jumped away. ]