Wow, how neat! I'm glad he's been doing well with you! Unfortunately, I do not know the species of this frog. Just be careful concerning the water; chlorine and chloramines, which can be present in tap water, is not good for frogs in the long term. Hobbyists often buy reptile water conditioner to remove harmful elements from tap water.

As for what you can do with him, you could always buy him a tank setup to keep him safe. You could even purchase some ABG (Atlanta Botanical Garden) mix substrate and plant part of the Pothos in there with him.