You can rename your water elemental

Just copy/paste the following into your chat bar:

/run PetRename("creative water elemental name here")

Just substitute whatever you want to name your water elemental inside those quotations marks, hit enter, and you're good to go. You must have the quotation marks around the name, and you must have the parentheses around the quotation marks.

Disclaimer: This only works once. That means if you try to fool around and name your big blue buddy something stupid to test things out, you're stuck with that name. Don't be the guy running around with a water elemental called "Bob." Unless that's a name you really like. Think carefully. Also, this may or may not be a bug, and it could very well go away the moment Blizzard decides to fix it.