TO filter or not to filter? The result of a recent study has some wilderness experts questioning whether water purification practices are always necessary in the backcountry.
It depends partly on who or what is up there with you, says Dr. Robert Derlet, a professor of emergency medicine at UC Davis, Sacramento.
Derlet, a backpacker for 50 years, sampled water from the wilderness areas of the Sierra Nevada over several years and reported the results of water analysis from 60 sampling sites in the spring 2006 issue of the journal Wilderness and Environmental Medicine.
He categorized sites by whether they were used most by backpackers or pack animals, cattle and sheep, and whether they were in grazing areas or natural areas that humans and domestic animals don't often visit.
Only one of 15 backpacker sites yielded coliform bacteria, Derlet says. The bacteria indicate a risk for harboring of microbes capable of causing human disease.
All 15 sites sampled downstream of cattle-grazing areas grew coliform, he found, and 12 of 15 sites with heavy pack-animal traffic did. All coliform bacteria he found were Escherichia coli, which can cause diarrhea.
The study produced important clues about when it's necessary to treat water in the wilderness, Derlet says, but its other important finding is that backpackers aren't primarily to blame for water pollution, at least not nearly as much as cattle are.
Backpacker Magazine also conducted a nationwide study of wilderness water several years ago, asking readers and its editors to collect samples all over the country. It published the results in December 2003.
"We were primarily testing for \o7Giardia \f7and \o7Cryptosporidium\f7," says Jonathan Dorn, the magazine's editor in chief. The organisms can cause intestinal distress. "The results were actually fairly positive. Only one location that actually flunked the test had enough pathogens to require filtering the drinking water."
But another expert always filters his water. "I just don't like to take a chance," says Dr. Robert Norris, editor in chief of Wilderness and Environmental Medicine and chief of the division of emergency medicine at Stanford University Medical Center in Palo Alto. "You just don't know what is above you."
For those following Norris' advice, the Centers for Disease Control and Prevention recommends three options for purifying your drinking water:
