Dechlorinated tap water is your best bet. Do not mix other species in with fire-bellies as they are quite toxic and any other frog housed with them is likely to suffer. As far as mixing other Bombina in with them, I would also say no. They are all toxic, but whether their toxins are similiar and thus safe to each other, I cannot say. So why take the chance? Also, outside of orientalis, we don't see the other Bombina species to othen here in the US. A while back I did see some albino B. bombina for sale on Kingsnake.com, but they were a little too pricey for my tastes.