User blog comment:Yonkou Rome/Devil Fruit Logia - Water?/@comment-1595565-20101016211145

I don't think it exists for two reasons. The first one is the reason you mentioned, it would be too powerful. All the user would have to do is surround another Devil Fruit user with water (kinda like Kisame's water prison jutsu from Naruto) and they would be dead. The second reason, is it wouldn't make sense in regard to the rule about Devil Fruit users being unable to swim. What would happen if the water logia user went in the water in elemental form? Would they merge with the water or return to their normal form and drown? It wouldn't really work.