Missing the point?
Terminal velocity is only part of the answer.
What matters is how fast you impact the water. The speed at which that is fatal isn't really anything to do with terminal velocity at all. After all, if you die when you hit water at 200kph does it matter whether you're going 201 or 500?
What's more interesting in this question is how water reacts when you try to break its surface: you can dive from a great height and be fine, but go a few metres higher and the water can't 'get out of the way' quick enough so you end up smeared on the surface. Obviously the shape of the object falling has an effect - pointy is more likely to break the surface than flat, etc. I'm sure the Navy has done some studies on torpedoes dropping from planes or something that would give us a hint as to the physics involved.
Come on - inquiring minds want to know.