72 percent of the Earth is covered by ocean. So desalination seems like a logical answer to drought, right? Not so fast.

[youtube http://www.youtube.com/watch?v=gA_XVxhBmTQ&w=600&h=315] California droughts right now might be the worst in 100 years, and Lake Mead's at a fairly dangerous level (which threatens tourism mecca Las Vegas), so clearly we're moving to the "answers" stage of our water problem. It would seem that the biggest option -- at least in terms of sheer num…