DWS would be related to cliff diving, which is covered here:
http://adventure.howstuffworks.com/outdoor-activities/water-sports/cliff-di... (not the same of course, but the physics of hitting the water are).
Quote from the article: "If you jump from 20 feet (6 meters) above the water, you'll hit the water at 25 mph (40 kph)"
Kinda makes you think twice about highball DWS. Or at least make sure you know what you're doing.