Safe Water in the Wilderness
The ARS Sojourner
It's been said many times, but it needs saying again: there's no way to tell from appearance if water is safe. Sparkling, clear water, tumbling over boulders as it cascades down a mountainside, may be safe. Or it may contain such disease agents as hepatitis viruses, Giardia cysts, or any number of others. All of these can make you very, very ill. Why take a chance of ruining your trip, or even worse?
There are several proven methods of water purification that are practical for field use. Boiling is the least complicated and requires no special equipment, assuming that you usually bring cooking gear with you on a multi-day trip. Simply bringing water to a rolling boil kills all disease organisms. Though the boiling point drops at higher altitude, the temperature is still high enough to do in the bad guys at any altitude you're likely to reach under your own power. However, boiling has disadvantages that discourage routine use. You'll use a lot of time and fuel, and are left with hot, flat-tasting water. Time cures the heat problem, and the taste can be improved by pouring the water back and forth between two containers. This restores the air that is normally dissolved in water.
Filtering is the most popular method of water purification. It works by manually pumping untreated water through a special micropore filter, which has pores so small that most organic material is removed from the water. Not only does micropore filtering remove dangerous organisms such as bacterial and cysts from the water, it also improves the taste by removing otherwise harmless organic material. Many filters incorporate activated charcoal elements, which act to remove odors and tastes from the water. Unfortunately, no filter can be made small enough to trap viruses, which are molecule-sized and pass through filters right along with water molecules.
Water purifiers add an active iodine element to the filter path, which kills viruses. The term "water purifier" is reserved for such filters, to distinguish them from systems that don't kill viruses. A filter is acceptable in areas that aren't likely to have dangerous viruses in the water, but to be safe, stick with water purifiers.
A drawback to any filter is that it eventually clogs up. The dirtier the water, the more rapidly it happens. All good filters and purifiers are field-maintainable, allowing you to replace or clean the filter element. Some also have prefilters, designed to catch silt and sediment before it reaches the microfilter. Filters are also slow. They seem to make the most sense for small groups, which can share the weight of the filter and delegate someone to pump water while others set up camp, cook meals, set up antennas, etc.
A third solution is chemical treatment. Both chlorine and iodine are very effective purifying agents, but iodine is the more practical because it's available in a stable, tablet form. One iodine water purification tablet treats one quart of water in 10 to 30 minutes, killing all bugs including viruses and cysts. A bottle of 50 tablets purifies 12.5 gallons of water and weighs about an ounce. The tablets do their work unattended, freeing you to do other things.
Many people object to the iodine taste, which is stronger than that left by an active-iodine pump purifier. Some brands of iodine tablets come with an iodine neutralizer tablet, which you use after the iodine has had time to work. This treatment removes the iodine taste completely. Ascorbic acid (vitamin C) is the active ingredient, which means that you can use powdered fruit drink mixes. This old desert hiker's trick not only eliminates the iodine taste, but also masks the alkaline taste common to desert water. Another method is to use dehydrated lemon slices, which are very light and take almost no space. A tiny piece removes the iodine taste from a couple of gallons of water.
The other problem with iodine tablets is that they don't filter yucky stuff like bits of moss, decayed leaves, and little swimming creatures (also known as "creebles") from the water. While the iodine zaps anything dangerous, chunky water is unappealing as a beverage, though it may be fine for cooking. My current solution is to filter the water through a coffee filter, if needed, before adding iodine tablets. Several of us have found that coffee filters work more quickly when supported in a genuine coffee filter holder, so I carry a cheap plastic holder with all extraneous plastic removed. Dirty water clogs coffee filters too, but the filters are very light and cheap, so I carry plenty and replace them as needed. Of course, paper coffee filters are not as effective as micropore filters, so the water may still have some color or taste from organic material. However, the iodine takes care of anything dangerous, and ascorbic acid improves the taste. The complete system- filter holder, 20 filters, iodine, and dehydrated lemon weigh 5.0 ounces.
Another iodine treatment method uses pure iodine crystals. The crystals are kept in a small bottle, which is filled with water. Elemental iodine is very slightly soluble in water, and after about an hour the solution in the bottle reaches saturation, containing just enough iodine to treat a quart of water. Iodine's solubility depends on water temperature, so the solution contains different amounts of iodine at different temperatures. With cold water, you must use more solution. A liquid crystal thermometer on the side of the bottle tells you how much to use. The method is by far the cheapest, but is very slow because of the wait for the solution to saturate after each use. Another disadvantage is the danger of ingesting iodine crystals, which are extremely poisonous. Commercial versions use a trap in the bottle to eliminate this hazard.
I've included a chart to help you compare different options and select the purification system that best suits your needs.
Bruce Grubbs, N7CEE, has been active in QRP for the last fifteen years, and enjoys
homebrewing, kit building, and field contesting. His favorite wilderness activity is exploring the Grand Canyon on trips of a week or more, and he also enjoys long backpack trips in the mountains of the west.