Honestly an awesome move. Won't see much arena usage due to the long charge time, but it's amazing nonetheless. Could totally see this in the anime! The water source part is cool as well, but sometimes it spawns actual water.
Excellent ability! This just ADDS to the resourcefulness of a Waterbender. I still think it's silly you can create massive waves from a small source, but I understand the amount of work required to make things logical, it won't effect the rating.