As we are largely comprising of water, in any situation, having potable water is very important, so a little survival tip from me, to help with this is, ..... if you need to filter water to be able to drink, it should be run through a good amount of spagnum Moss ( I have no idea if that how you spell it! ) Its the moss that you often find tied around Christmas wreaths or used in hanging baskets, to give you an idea what it looks like. :-)