Firstly, there have been a few advocates ( aka idiots) who claim you can. A french physician conducted experimental liferaft journey in the 1950s and supposedly survived by drinking saltwater. The Kon-Tiki expedition also claimed drinking small amounts was possible. I've only had one occasion to openly challenge this dangerous falsehood. A BOATING SAFETY INSTRUCTOR claimed it could be done. I grabbed a glass, filled it with fresh seawater and handed it to him. The immediate result made his audio visual training aids pale. I'm rusty on my lecture, but simply put the human body is almost a duplicate of the ocean. Dry us out like a mummy or those characters in DUNE and you have seawater. But, a massive salinity increase disrupts the natural cellular osmosis. Try putting guppies into a salt water aquarium and see how they react- if Bill Van doesn't rescue them first <img src="/images/graemlins/blush.gif" alt="" />. Our M.D.s and medical personell will probably explain this better. Basically, having recovered people who did, you go into delirium as your brain and then quickly major organs shut down . I also had the priveledge of meeting a U.S.S. Indianapolis survivor. He still had the lifevest and would quietly put it on whenever stressed. He also had a LARGE canteen with him constantly. This was in pre bottled water days. Nobody thought less of him who knew his background.