Having spent a good deal of time in some of the 'rougher parts' of Central America, I'm somewhat familiar with water purity problems. Physical filters work well against everything but viruses. For that one needs chemicals, boiling, or UV-C light
. While a little expensive ($75 to as-much-as-you-want-to-pay) UV water purifies are effective if used correctly. There are many models of UV water purifiers that work on 12v, and some that even work on small lithium or standard AA type batteries. One such small battery
model that I've seen used is the SteriPen (around $100 from sources like Amazon or REI). It is a small hand-held device that one can use in a water glass, cup, bottle, etc. (handy for treating water in a restaurant or hotel room setting, just stick it in the glass, turn it on, and stir it around for a minute). The UV light
must hit the cooties to do away with them, so it is much less effective if used with dirty water, water with ice in it, water with things like lemon wedges, or water with anything that can cast a 'shadow of safety' for the cooties. The upside is it is quicker than boiling and doesn't add any taste like chemical treatment. Happy camping!