Since we are surrounded by large bodies of Salt Water, we should all have a basic concept of how to turn the salt-water into fresh water. The link below will provide a very basic way to accomplish this. In college chem class we would place the salt water into a ceramic container and boil the water off. Steam would be funnelled into a copper tube and the condensation would drain into a cup....VOILA! When all the water was gone, we would have one container of fresh water and the original ceramic container that held the salt water would have only the salt remaining. Keep in mind that the yield is low but the technique is simple and if SHTFLI, and all the booji water is gone and power has not been on in a few weeks, this may be the only way!
Enjoy the read....
http://science.howstuffworks.com/environmental/earth/oceanography/desalination.htm
