Each day about 5,000 campers are in the Boundary Waters Canoe Area Wilderness in northern Minnesota, with several hundred more at the 2,200 campsites in the Quetico wilderness across the border in Canada. All have in common the question of how to handle their drinking water.

There will be a small percentage who live dangerously and drink straight from the lake, although both U.S. and Canadian officials strongly advise against it. The water looks and tastes clean, but within it lives microorganisms and, less likely, toxins, that can make a person mighty sick.

The illness campers worry about most is giardia lamblia, sometimes called "beaver fever." The pathogen is a protozoa from animal or human feces and it is responsible for tens of thousands of illnesses — diarrhea, abdominal pain, bloating, other fun stuff — each year. Since the incubation period is anywhere from one to four weeks, the poor camper often doesn't get sick until getting home.

A comparison of treatments
Treating the water can take care of the protozoa, but how best to do that? An article by Nancy Pietroski in the summer issue of Wilderness Medicine tackles the question of comparing water treatments. The winner seems to be...

Boiling. That was your grandpa's water treatment, if he bothered, and Pietroski calls it "most reliable at pathogen killing." The inconvenience factor is that boiling uses time and fuel.

The article (PDF) summarizes five other treatments, including iodine, filters, ultraviolet light, chlorine dioxide and chlorine tablets.

All have disadvantages: Iodine tastes bad, filters are not effective against some viruses, ultraviolet systems use batteries and need the particles removed from the water first, chlorine dioxide needs more testing in the field, and chlorine tablets are not effective against giardia.

Each method also has advantages: Iodine kills bacteria (think E. coli), viruses and giardia, filters remove giardia and other protozoa, ultraviolet light is highly effective against protozoa, viruses and bacteria, chlorine tablets kill bacteria and viruses, and chlorine dioxide is effective against all microorganisms.

"Methods should be reliable, convenient, and not add a burden to your load," Pietroski writes.

The article traces concern with backcountry water safety in the U.S. to a 1976 outbreak of giardiasis among campers in Utah.