Potability of backcountry water
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The potability of backcountry water is uncertain, although scientists generally believe that the threat of water-borne disease from drinking untreated water in the backcountry has been grossly overstated.
Yet it is widely believed among backcountry users, that much of this water is actually unsafe to drink. While this may be correct, there is little public health or scientific literature to confirm this belief, and much literature that contradicts this view.
A recent large-scale review attempted to include all relevant epistomological literature by T. Welch of the Tulane School of Public Health. Welch concluded that water filters and other treatment is generally not necessary in the U.S. backcountry [1].
Elsewhere, in a paper for the Wilderness Medical Society [2] , Welch writes:
It must be impressed upon backpackers (just as it is impressed upon health care, food industry, and daycare workers) that stopping hand-to-mouth spread is the key to preventing gastrointestinal infection. Diluting this message with unfounded concerns about wilderness water quality or the relative merits of various water-treatment methods serves no useful purpose
Welch claims:
The most comprehensive recent look at the problem was not in the medical literature, but rather in the lay magazine Backpacker.11 The editors of this widely read publication sampled several backcountry waters for 2 pathogens (Giardia and Cryptosporidium) commonly worried about in the backcountry. Although a few areas yielded positive isolates, in each case the concentration of pathogens was below that which would be expected to result in disease with casual (as opposed to ongoing) use. The highest concentration of G lamblia found, for example, was 1.5 cysts per liter. Even if one happened upon this spot, it would take nearly 7 L of water consumption to achieve the minimum infective dose of this organism.
Large rivers may be tainted with pesticide runoff and industrial pollutants from sources far upstream, but water in the backcountry, where people usually go for hiking or backpacking, originates nearby and is free from these hazards. The most common danger is microbial, and this may come from natural or human sources.
In most parts of the world, water may contain bacterial or protist contamination originating from human and animal waste, or sometimes from dead animals in or near the water. Giardia lamblia and Cryptosporidium spp., both of which cause diarrhea (see giardiasis and cryptosporidiosis), are common pathogens. Viruses may also be found in water, but are not common in developed countries.[citation needed]
Although backcountry water is not routinely tested as a public water supply is, tests that have been done in the Sierra Nevada of California found low levels of coliform bacteria such as Escherichia coli. Many samples showed no coliform bacteria at all; others showed more, especially in areas with cattle gazing or heavy human activity.[1]
Robert Rockwell, an engineer by training, has made a similar, ongoing review of scientifc literature. Rockwell quotes James Wilkerson's Medicine for Mountaineering and Other Wilderness Activities. (The Mountaineers, 4th edition, 1992):
- "In recent years, frantic alarms about the perils of giardiasis have aroused exaggerated concern about this infestation. Government agencies, particularly the U.S. Park Service and the National Forest Service, have filtered hundreds of gallons of water from wilderness streams, found one or two organisms (far less than enough to be infective), and erected garish signs proclaiming the water hazardous."
Rockwell's survey of literature pertains in particular to the Sierra Nevada, where he concludes that untreated surface water is generally safe to drink. He believes the survey has similar implications for other backcountry regions in the U.S. and Canada.
Rockwell notes that "Giardia and other intestinal bugs are for the most part spread by direct fecal-oral or food-borne transmission, not by contaminated drinking water. Since personal hygiene often takes a backseat when camping, the possibility of contracting giardiasis from someone in your own party someone who is asymptomatic, probably is real. Recalling that up to 7 percent of Americans, or up to 1 in 14, are infected, it is not surprising that wilderness visitors can indeed come home with a case of giardiasis, contracted not from the water...but from one of their friends."[2]
[edit] See also
[edit] References
- ^ Robert W. Derlet, MD; James R. Carlson, PhD; Mikla N. Noponen, MD (2004). "Coliform and Pathologic Bacteria in Sierra Nevada National Forest Wilderness Area Lakes and Streams" (abstract). Wilderness and Environmental Medicine 15 (4): 245–249.
- ^ Giardia Lamblia and Giardiasis by Robert L. Rockwell, June 4, 2003, Loma Prieta Chapter of the Sierra Club website. Accessed Nov 6, 2006.
