Sorry to revive this old post, but judging from Paranet Papers, it's highly probable that Aquamancers and water witches/warlocks summon their water from the Nevernever when they are not controlling an earthly source. Will also theorizes that it acts as real water until it is no longer being powered my magic, as "it dries up quick, without much of a trace."

I might rule that using it as a binding method for magic would only work if you were further empowering it with your own energy, plus maybe a portion of what it is binding? It wouldn't be energy-efficient, but it would stay within physical laws (can't get something for nothing).