Hajime's still stuck as a giant bug, going to go stir crazy and make a really ill-advised jaunt outside for a little bit, and probably be a strange occurrence in and of himself. But at least he'll be able to turn human again after drinking the water. |D

Arthur will be drinking the water, and he'll be getting some water-related power back, probably breathing underwater because nothing could go wrong under these circumstances.

I'm not sure what Mort will be doing. He's still a little mopey now that his brother's gone, and he'd probably have one doozy of a memory flashback if anyone were to be near him if he drinks the water.