[mpipes]

***Nerd alert***

Assuming a depth of 12 inches, at sea level the pressure of the water would be about 104.3kPa which translates into 15.1psi or only .4psi more than atmospheric pressure.

Using a regularly accepted Body Surface Area figure for an adult male of 1.8m^2 , that's ~2800sq.in.

So 2800sq.in x .4psi yields 1120lbs of total compressive force against the body. That's assuming full submersion at 12" but given the depth will vary with body thickness, pitch, and moving arms/legs, there's still going to be substantial pressure on the body even at shallow depths. Of course the story changes when you go buoyant.