The water would definitely be an issue, maybe perhaps the bit that was in his mouth didn't have the virus but I kinda doubt that. Then again, I don't really understand how a virus would spread in water, would the entirety of the water become infected, would it only be patches of it, would it slowly spread till it reached everything, I'm honestly not sure.
Also, mad props to the artist for that panel where all the zombies are floating underwater around Ke'er, that shit is genuinely haunting. With some more attention to detail / for lack of a better word, "quality", that could genuinely be horrifying. Like if it were in the art style of those old 'Scary stories to tell in the dark' art, oof, just oof.