On a course I did the instructor mentioned a long term session in a liferaft where the couple, one being a medic, used saltwater introduced through the botty ! whereby the salt was filtered out and fresh water absorbed by their bodies, not all bad because they could supplement this by drinking the moisture from fishes eyes that they caught, I think the other person was a biologist or similar, they knew not to eat salty flesh but just the good bits, sounds like fun, eh ???