I'll expound upon my earlier reply:
>boil it. Kills everything. Water tastes flat, often metallic. But it kills everything. If you have a heat source, a container that won't melt, and a heat source, this is by far the simplest way to purify water
>Chlorine Dioxide drops or tabs. Best tasting chemical treatment I've tried. Better than bleach or iodine. Downside is you have to mix part A and B and, theoretically, let it react for 5 min. before adding to water, then wait 15-30 min. for water to be totally safe. Tabs require no mixing, but still have a wait time and are costly. Longer wait times or greater concentrations recommended for especially turbid or cold water.
>UV. Scrambles the microorganisms' DNA (or is it RNA? I'm many, many years out of BIO) so they can't reproduce.. Takes about 1-2 min for a liter with a SteriPen or equivalent, but they are costly and require batteries. Am emergency field method if you have thin-walled, narrow clear-plastic water bottles is to fill them and leave them set in direct sunlight for 6-hrs or so, maybe less, idk. Hard to get high volume this way, though, in the field, though this is one method they are trying in the third-world to meet the need for simple, inexpensive, non-resource-intensive purified water.
>Filter: various types and models. Not terribly user friendly, and filters vary in quality, effectiveness, ease-of-use, compactness and weight, etc. Most filters don't filter viruses; if you need this feature, make sure you get the right filter, or combine it with chemical treatment. Generally bulky and heavy. Initially expensive, though you'll get hundreds of gallons out of most filters if you use them as directed and perform some basic maintenance.
Aside from pump-filters, there are gravity-fed filters (best for base-camps and larger groups), and several products that incorporate a filter or UV device into a drinking container or straw. I don't have any experience with these, so don't know how well they work.
