Filtering and Treating Water in the Wilderness
One of the most important tasks that an outdoor enthusiast may face is properly treating water for drinking. It's difficult, if not impossible, to carry an adequate supply of water with you on anything more than a day hike and most backpackers, paddlers and others rely on backcountry water sources for their hydration. The trouble is that almost all surface waters have microorganisms that, in high enough concentrations, will cause illness. The clear, cool water coming down from a waterfall may seem safe and refreshing but it may also contain nasty pathogens that can cause anything from mild discomfort to serious illness. Since there's no practical way to test the water for microbes, it's best to assume the water is contaminated and treat it.
Contaminants can take the form of microbes, chemicals or heavy metals. Generally speaking, microbes cause the most concern when treating wilderness water. Microbes, measured in microns (millionths of a meter), are usually divided into three categories based on their size - protozoa, bacteria and viruses.
Protozoa are the largest microbes and are thus the easiest to filter out. They range in size from just over one micron up to 15 microns. Giardia and Cryptosporidum are probably the best known microbes in this category. Cryptosporidium is a particularly hardy cyst that's resistant to some chemical treatments and can survive for several seasons in a pond or stream. Cryptosporidium can be treated with chlorine dioxide, mixed oxidants, UV light, and boiling.
Bacteria such as E. coli or Salmonella are in the next group and range in size from .2 microns to 10 microns. Although not as tough or long living as protozoa, bacteria reproduce more efficiently, are often found in greater concentration at a source of water and can be spread by both animals and humans. Bacteria can be filtered or treated with chemicals, boiling or UV light.
Viruses such as Hepatitis or Norwalk are quite enduring and can survive months in the water. Viruses are usually of more concern in under-developed countries with poor sanitation but can be found anywhere where there's been a human presence. Viruses are too small to be filtered and must be deactivated with chemicals, boiling or UV light.
The two terms most often associated with treating water is filtering and purifying. You'll find a large assortment of filters and purifiers available, each with individual advantages and disadvantages. You'll need to decide what works best for your particular activity and location. Day hikers may want to keep some chlorine dioxide tablets on hand for emergencies, while backpackers will want a pump filter for daily use.
Water filters mechanically filter contaminants from the water and vary in capability. Some (especially the emergency type) only filter the larger protozoa and bacteria while others (many of the pump type models) eliminate practically all protozoa and bacteria over .2 microns. Also, many have a carbon stage that can reduce or eliminate harmful chemicals and improve the taste and smell of water.
Filters provide a quick way to keep your bottles and reservoirs full without long wait times and will filter many liters before they need to be replaced. However, if you are in an area that is likely to have waterborne viruses and want complete protection, you'll need to employ either a chemical or UV light treatment after filtering since viruses are too small to be filtered.
There are several features to consider with filters:
Size and weight
Field cleaning and serviceability
Ease of use
Direct connection to container
Purifiers are a mixed bag and range from small tablets to all-in-one bottle systems. Purifiers inactivate viruses and microbes by chemical, UV light and other methods, and can be used in conjunction with filters.
Iodine - Iodine based treatments have been used for years and are effective on bacteria, viruses and some protozoa like Giardia but not Cryptosporidium. Potable Aqua and Polar Pure are the best-known iodine treatments. The negative taste from iodine treatments can be reduced with the addition of neutralizing tablets. Iodine based treatments should not be used long-term or if you are sensitive to iodine. Opened bottles should be used or discarded within one year.
Chlorine Dioxide - Chlorine dioxide treatments are available as tablets or drops and are effective against viruses, bacteria and cysts like Cryptosporidium. Additionally, chlorine dioxide does not add a bad taste and may, in fact, improve the taste of the water. However, because the Crypto cysts are so tough, you'll have to give the chlorine dioxide gas four hours to breach their defenses. Chlorine tablets are packaged in a tough foil so it's a good idea to have a knife or scissors handy. Once you've opened the foil around a tablet it should be used immediately.
Mixed Oxidants - The MSR MIOX purifier deactivates viruses, bacteria, and protozoa like Crypto in water by using a powerful dose of mixed oxidants. A brine solution is created from untreated water and salt through which the MIOX unit delivers an electrical charge, creating a mixed oxidant solution. The solution is then mixed with your untreated water and, after the appropriate dwell time (15 minutes to 4 hours depending on your target pathogen), the water is then safe to drink. The treatment does affect the taste of the water. The MIOX is rated for up to 200 liters per set of batteries and one ounce of salt.
Ultraviolet light - Purify water with UV light, a quick and easy way to disable all microbes in water. Fill your bottle with water and push the button. Some units will disinfect one half-liter of water in about 48 seconds. UV light destroys the DNA of microbes rendering them harmless. UV light does not alter the taste of water. UV purifiers have found a niche with international travelers who are uncertain about the local water, bottled or not.
Boiling - Boiling is perhaps the most low-tech method and also one of the most effective. If you have a stove or fire and a metal container, you can purify water by simply bringing it to a boil. The CDC recommends a vigorous boil for one minute, three minutes at altitudes over 6562 feet. Boiling will kill any microbes lurking around, including viruses.
Read the fine print
It is imperative that you read, understand and follow the directions for whatever treatment choice you make. Water turbidity and temperature often affect the efficiency and duration of treatment. Chemical treatments have shelf lives and, in the case of iodine, an opened bottle life. Filters should be cleaned and stored according to instructions to prevent bacterial growth in the filter. Filter hoses and prefilters should be packed to avoid cross contamination with "clean" filter components. Make sure that you know how your filter or purifier works and its effectiveness.
A separate but related topic is hand washing. It's been suggested that some post-excursion illnesses attributed to contaminated water should be blamed on improper hygiene instead. In any case, it's only smart and courteous to your fellow hikers to use hand sanitizer before preparing food or water as well as each time nature calls.