I had an argument with a friend and fellow engineering student the other day about the properties of water in a high-speed impact. It started when I casually mentioned that water (like the new item from thinkgeek.com that we were discussing) exibits different properties at different impact speeds, because of its polar nature; and that further, striking a body of water at sufficient speed was like striking concrete. He refuted this theory on the grounds that striking any surface at high enough speeds would cause enough decceleration to damage the human body just as concrete would, and that it has nothing to do with the properties of water. I originally heard this from a friend who was a Navy rescue diver, and again from one of my professors, and I've always taken it for granted, but I could be wrong here. My friend challenged me to do the research and find any studies that backed up my claims, but I'm drawing a blank so far and I'd like to see if anyone can prove this one way or another with pure physics. Thanks in advance!