Water Treatment Methods
Water can play a major role in the transmission of enteric infections, and virtually all of the agents that cause travellers’ diarrhea may be present in contaminated water. Anywhere that trekkers are able to travel these days, people live or travel higher up; all ground water should be assumed to be contaminated. Travellers wishing to avoid diarrhea should not consume untreated water. Various water treatment methods are reviewed below.
Bottled Water
Bottled water is only as safe as the source. There are recorded instances of contaminated bottled water contributing to cholera epidemics. In an unpublished study performed in Kathmandu, randomly purchased bottles of various brands of water were cultured, and a significant percentage grew enteric pathogens (diarrhea-causing organisms). Carbonated water is acidic enough (due to the dissolved carbon dioxide) to kill contaminating bacteria. Bottled water has the disadvantage of being an additional expense, and is not always available. Trekkers should not from rely on bottled water for the simple reason that all of these plastic bottles are carried into the mountains, and none are ever carried out, producing a tremendous and completely unnecessary waste disposal problem.
Heat kills microorganisms, and virtually all enteropathogens are readily killed at temperatures well below the boiling point. The process of heating water to a boil makes it hot enough long enough to disinfect it, even at elevations as high as Everest Base Camp (references 1,2). There is no need to boil water for 5 minutes, 10 minutes, or 20 minutes, as some guide books recommend! Bringing water to a boil is adequate for disinfection.
Chemical Treatments
Chemical disinfection of water depends on the killing of bacteria, Giardia and amoeba cysts, and viruses by the chemical. Halogens (chlorine and iodine) are most commonly used.
Chlorine
Chlorine has been used for several centuries for water disinfection. The most common objection to it is the flavor, though there have been some suggestions that it is unreliable in killing Giardia cysts in the commonly used concentrations.
Halazone tablets
These are convenient and inexpensive, but have several disadvantages. Due to its chemical formulation, reliable disinfection in all conditions requires 6 tablets per liter for 1 hour contact, resulting in poor flavor (Backer 1995). The tablets rapidly lose effectiveness when exposed to warm, humid air.
Superchlorination-dechlorination
This two-step method is somewhat inconvenient, and the chemicals needed are destructive to clothing and gear if spilled, but it is highly effective and results in nearly flavorless water. High concentrations of chlorine are initially developed, and then in a second step removed by the addition of peroxide.
Iodine
Iodine has been used to disinfect water for nearly a century. It has advantages over chlorine in convenience and probably efficacy; many travellers find the taste less offensive as well. It appears safe for short and intermediate length use (3-6 months), but questions remain about its safety in long-term usage. It should not be used by persons with allergy to iodine, persons with active thyroid disease, or pregnant women.
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