No, you dont die when your under the water. if your looking for a good canvas for building underwater, look at the thread on here titled deep...
actually, to my knowledge, you are the first to post a canvas map of the underwater area in Forgehub at the least. I've not seen it on here, even...
I personally mapped out the deepwater area myself not too long ago, and i found that you are about dead on to the size of the diving zone, as i...