There are also images like post #1168373, which doesn't really have something to tag water.
I also don't see the gain in tagging many of the images that are tagged underwater with the water tag, like post #179501. Given that it is everywhere in the image, it really loses its value as an object worth tagging. In many cases the only thing giving it any identity is other objects present (bubbles, surface sunlight etc) within the image (ex: post #1069270).
