Looking back, I realize that not only was that an afternoon of fun, but an afternoon of physics as well. Since the water slows us down as we deccelerate to a final velocity of 0 m/s, the amount of time it takes is greater than it would be if we were jumping onto a hard surface.
Impulse= force times time
Since the water allows us to come to a stop slowly, the amount of force we feel as we hit the water is minimal. If we were to jump onto a hard surface, then the time it takes to come to rest is much smaller. Since force and time are inversely related, the amount of force we feel when we jump onto a hard surface is much greater. Good thing we dont feel very much force when we jump into water, or some of these jumps would have hurt.