Why you are connecting it to water is because in Latin, "hydra" can be any water snake and in Ancient Greek, "hudor" means water.
EDIT: Maybe we can try to turn this back to discussing Sims 3 usernames?
If you're referring to me (one other referred to snakes; I used 'reptilian' which still fits
) it's because 1. I'm more familiar with Latin, though by no means an expert and 2. if you used hydra in an English word (or to start it) it usually refers to water. Examples: hydrate, dehydration, and, uh, I'm sure there are others though looking it up on dictionary.com, I see it originates from 'hydr' and we're back to the Greek again.
My mention of them never giving us pet snakes in the game was my lame attempt to get back to the Sims.
I think I said this already somewhere, but my username is from one of my favorite big cats: neofelis nebulosa, commonly known as the clouded leopard, though it's kinda tied with panthera onca (jaguar) in the bid for first place for me. I didn't want anyone mistaking me for a die-hard Pantera (the band) fan, so I went with NeoFelis. I do like rock and metal (amongst other genres), but I just can't think of any song by them I like, at least not off-hand. No offense intended to Pantera fans. Because of the popularity of The Matrix series, I don't want to be called Neo. Nothing against the movies (though I only saw the first one) but I'd prefer people call me by my full username so there's no confusion. I include myself in that category, because if someone here referred to Neo and meant me, I might not realize it.