You should still try it, but I have a sneaking suspicion that Kinect's form of depth tracking wouldn't work very well (if at all) in water. It sprays out a pattern of infrared dots, and uses the distance between those dots (very simplified, this) to determine distance. Water refracts light differently, and would probably confuse the hell out of a Kinect.
i don't think it wont work because of different refraction in water. Isn't that problem only occuring if you let it "look" through the change of medias? I mean, we see quite normal under water, don't we? Only if we look into the water our eyes being in air, we see the refraction problems. right?