@JeremyECrawford So, I've heard the question brought up quite often. I personally rule it as no, since it is too powerful of an effect for such a low level spell. HOWEVER, in an attempt to settle the debate, does Create or Destroy water damage Water Elementals?
— Anthony McGraw (@AnthonyMcGraw89) January 26, 2018
The create or destroy water spell can destroy up to 10 gallons of water in an open container. A water elemental is not water; it's a creature. #DnD https://t.co/BJ4FeqrvTe
— Jeremy Crawford (@JeremyECrawford) January 26, 2018
I assume this logic safe to apply to other "classes" as well. The base class of a Water Elemental is an Elemental, but it's "affix" -or "subclass"- is Water.
Thus a Fire Elemental would not be affected by Destroy Fire, nor would an Earth Elemental by um, a Bulldozer… spell…?
— Forrest G Emerson (@StabbyGM) January 26, 2018
Monsters are creatures. Spells and other effects that target objects or environmental phenomena are ineffective against them. #DnD https://t.co/JlJgVIxBoI
— Jeremy Crawford (@JeremyECrawford) January 26, 2018
Yeah no. With respect, this is far too ludicrous literalism for my tastes. A WATER elemental is by definition WATER, from the Elemental Plane of WATER, not water-appearing non-water substance. Either living water or spirit-animated water. Sometimes a cigar is just a cigar! I gave you our story intent. An elemental of whatever kind is an extraordinary creature associated with an element, but it is not that element. You're definitely free to alter that story in a campaign you run.
— Jeremy Crawford (@JeremyECrawford) January 26, 2018
If I had to make an assumption I would say it would match the fire elemental. In the manual it states that fire elementals are damaged for 1 cold damage for every gallon of water dumped on it. So you could say for every gallon of water destroyed the water elemental would take 1 fire damage or force damage.
the “destroy water” part reads:
“You destroy up to 10 gallons of water in an open container within range. Alternatively, you destroy fog in a 30-foot cube within range.” I don’t know if people have missed the obvious, but it does state “in an open container” some time the answer is right in front of us but we overlook it. most spells answer themselves with the most minor of things, so unless you can put and keep a water elemental in an open container like, I don’t know what hold ten gallons, a bath tub or barrel I don’t think this argument is even necessary unless WotC are ruling lakes, rivers, and the entire ocean as containers.