Not exactly, but sort-of. First of all, boiling is best if you can find a natural container in which to boil water.

I know I touched on this in the other thread it probably fits better in this thread. Charcoal filtering is one natural method considering that all you really need is wood and fire in order to make charcoal. Another method (though I personally do not recommend it) is evaporation/condesation methods such as a solar still.

In a lot of situations nature has already done the filtering for you if you know where to look. Morning dew is a great example of naturally clean water, provided you aren't pulling the dew off poisonous plants. Rain water is also relatively clean provided that you aren't in an area known to have excessive amounts of air pollution. These are not the only types of natural filtration. Sand, rocks and certain animals also help clean your water under the right circumstances. It is way too complicated to explain in one reply (at least with the time alotted to me while I type this from my desk at the office <img src="/images/graemlins/smile.gif" alt="" /> ) but the information is out there. Many of these techniques aren't simple and you have to know where to look and a high stress survival situation makes it even more difficult. However, if can be done and the more you learn and practice what you learn, the better off you'll be when in need.

Also keep in mind above all else. Three days (give or take) without water and youre dead and long before that you'll be in really bad shape, so drinking even the nastiest water is WAY better than none at all!