Well as far a clarity goes, if you are stuck in the woods always boil it, but if ya can't, lets say you find an old stagnant pool of water. You can dig down next to it and let the water seep up through the ground, this will normally make it somewhat safer to drink as the ground acts as a natural filter, but it ain't the safest way. This is a desperation way of doing it .. Now I have done it myself, and still do at times but boil it that is the only safe way. Ya can do the old injun trick and that is heat up some rocks and pop them into the water, that brings it to a boil or close enough to kills all the bad critters in it.