http://www.msnbc.msn.com/id/27768967/
Thought this was interesting.
For those of you that can't get the link for whatever reason, here's the short-n-skinny:
Dude (Harvey Lillywhite from the University of Florida) based his findings on lab and field observations. In the lab he kept the snakes away from freshwater for 2 weeks (at which point the snakes showed dimples and other signs of dehydration), weighed them, let them go in a tank of saltwater for up to 20 hours and then weighed them again to see if they drank. They didn't gain "an appreciable amount of weight."
He did the same thing with freshwater instead of saltwater, and most of the snakes immediately drank. Further testing showed they accept highly diluted saltwater also. Apparently sea snakes are most commonly found in areas with large amounts of rainfall, and scientists are thinking that they drink the diluted saltwater at the surface during and after rain.