All water found in nature should be treated if possible (even well water if you plan on drinking it, though I drank untreated well water all my life and I am ok, I think), if you don't have the stuff to treat it then drinking fresh rain water from rocks, dew gathered from leaves, ect carries less of a chance of making you sick then drinking, say, river water. Which is important because you don't want to get sick while you are trying to survive. There is always the risk of getting sick, you are just trying to lower your risk.