Most authorities recommend that you boil, filter,
or chemically treat all water taken from a questionable source. That’s sound advice, providing
you have the necessary chemicals and/or equipment
plus the self-discipline to use them.
Although I occasionally boil (160 degrees will kill
almost everything) my drinking water on backcountry
trips, I confess to laziness in this
respect. As often as not, I drink untreated water,
but I am very careful where I get it. Here are the
guidelines I religiously follow:
Filters and Purifiers
Filters strain out microorganisms, but they don’t
kill them. The critters are just trapped and held
inside the filter. Eventually, the filter loads up
(water flow decreases), and you have to clean or
replace it. Filter pore size is the nemesis of all filtration
units. Pores small enough to trap the tiniest
microbes impede water flow and pumping efficiency; large pores let more water through—
and possibly some dangerous germs too!
Purifiers kill microbes with chemicals, but
they don’t filter them out.
Enter the purifier/filter. It has moderately
sized pores that allow a fast flow rate, plus a
chemical that kills microbes that pass through
the filter. The downside is an often chemical
aftertaste that can be reduced (but not entirely
eliminated) with a final carbon filter.