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by Rick Curtis
first edition published by Random House March, 1998
Dipping your head into a cold mountain stream and taking a long refreshing drink is an experience that has basically vanished from the wilderness areas of America. With the increased use of the wilderness there has also been an increase in the amount of bacteriological contamination of backcountry water supplies. The U.S. Environmental Protection Agency reports that 90 percent of the world’s water is contaminated in some way. There are a variety of microscopic organisms that can contaminate water supplies and cause potentially serious, even fatal, illnesses among wilderness travelers. The major danger in the backcountry from these infections is fluid loss due to diarrhea and vomiting, which can lead to hypovolemic shock and possibly death (see Diarrhea or Vomiting, page 315; Fluid Electrolyte Replacement, page 286; Shock, page 238).
In order to drink the water, you should be prepared to treat it. There are numerous methods of water purification, described below in order of effectiveness. Remember, however, that infections can also be spread through poor personal hygiene, something that purifying your water won’t prevent.
Biologically contaminated water is water that contains microorganisms such as Giardia (a common microorganism that, if not killed, leads to intestinal disorders), bacteria, or viruses that can lead to infections (see Gastrointestinal Infections, page 316). Toxic water sources contain chemical contamination from pesticide runoffs, mine tailings, and so on. Boiling, filtering, or chemically treating water can remove or kill microorganisms, but it will not remove chemical toxins. This is also the case when using a solar still (see page 223).
Boiling is the most certain way of killing all microorganisms. According to the Wilderness Medical Society, water temperatures above 160° F (70° C) kill all pathogens within 30 minutes and above 185° F (85° C) within a few minutes. So in the time it takes for the water to reach the boiling point (212° F or 100° C) from 160° F (70° C), all pathogens will be killed, even at high altitude. To be extra safe, let the water boil rapidly for one minute, especially at higher altitudes since water boils at a lower temperature (see page 68.)
There are two types of chemical treatment: those using iodine and those using chlorine. There are a variety of products on the market, so follow the directions on the bottle. Be advised that many of the tablets have an expiration date and become ineffective after that point. Also, once the bottle has been opened, the tablets must be used within a certain period. When in doubt, buy a new bottle. Remember that chemical purification methods may only be partially effective, depending on the water temperature.
Iodine is light sensitive and must always be stored in a dark bottle. It works best if the water is over 68° F (21° C). Iodine has been shown to be more effect than chlorine-based treatments in inactivating Giardia cysts. Be aware that some people are allergic to iodine and cannot use it as a form of water purification. Persons with thyroid problems or on lithum, women over fifty, and pregnant women should consult their physician prior to using iodine for purification. Also, some people who are allergic to shellfish are also allergic to iodine. If someone cannot use iodine, use either a chlorine-based product or a non-iodine-based filter, such as the PUR Hiker Microfilter, MSR WaterWorks, or the Katadyn Water Filter.
Generally, the procedure is as follows:
Chlorine can be used for persons with iodine allergies or restrictions. Remember that water temperature, sediment level, and contact time are all elements in killing microorganisms in the water. Halazone is an example of a chlorine tablet product. To use, follow the manufacturer’s instructions.
Tricks of the Trail
There are a number of devices on the market that filter out microorganisms. A water filter pumps water through a microscopic filter that is rated for a certain-size organism. The standard size rating is the micron (the period at the end of this sentence is about 600 microns). Depending on the micron rating of the filter, smaller organisms (like viruses) can pass through. Be cautious when selecting a filter. You should know what potential organisms you need to treat for. You don’t want to go to an area where a virus like hepatitis A is present in the water (a problem in some developing countries) with a filter that will handle only a larger organism like Giardia.
Organism
Examples
General Size
Filter Type
Particle Size Rating
Protozoa
Giardia, Cryptosporidium
5 microns or larger
Water filter
1.0–4.0 microns
Bacteria
Cholera, E. coli, Salmonella
0.2–0.5 microns
Microfilter
0.2–1.0 microns
Viruses
Hepatitis A, rotavirus, Norwalk virus
0.004 microns
Water purifier
to 0.004 microns
There are two basic types of filters (descriptions of several popular models begin on the facing page).
Note: There is a difference between a water filter and a water purifier. Filters do not filter out viruses, but there are water purifiers, like the PUR Scout, that pass the water through both a filter and an iodine compound that kills any smaller organisms that have passed through the filter. These purifiers kill all microorganisms down to 0.004 microns; however, the filter should not be used by people who are allergic to iodine.