Water treatment is a little bit like snake bite cures. Since not everyone really gets sick, a lot of questionable methods seem to work, and thus acquire a lot of anecdotal support.<br><br>Boiling is the most definitive way of dealing with bacterial contamination, which is probably overall the greatest general problem. The old saw about 5 to 10 minute boiling has been refuted by James Wilkerson, MD, author of Mountaineering Medicine. The longer interval arose from the need to sterilize bandages, which does require the longer interval to deal with special septic bacteria which are a problem in that context.<br><br>It is of academic interest to note that there are extremophile bacteria that thrive, not just live, in boiling water, like the bacteria from Yellowstone NP that have proved so useful in PCR DNA studies. Luckily these bacteria don't give us gut feelings.<br><br>Thirty to forty years ago, I used to drink willy-nilly from all sorts of clear, sparkling mountain streams inthe SW. I never got sick. I am much more cautious now. Filters eem to work fine, meaning I have never gotten sick, with most sources. They are quick and convenient. Boiling has worked for me with such sources as water drawn from open irrigation ditches in SE China, so that is my preferred method - definitive and requires no extra equipment. The NPS put out a brochure on water treatment recently and they stated that boiling was the surest way to purify water. If you can't trust a ranger, who can you trust?<br><br>Some of the contaminants of concern, like heavy metals, probably aren't an issue unless you will use the water for an extended period of time, as opposed to a canteenful while passing through (unless arsenic is present!). I have used some very questionable sources, reasoning that the water might make me sick, but it will get me to town, where I can be cured. Dehydration can kill within hours; everything else is treatable.