This is the most reliable method, although stoves, kettles and heating coils may be inconvenient to use while travelling. Boiling for one minute is sufficient to kill all harmful organisms (although just reaching a rolling boil is usually enough, long boil times just wastes water), even at high altitude when water boils at a lower temperature.
Iodine (now banned in the EU since October 2009) Iodination is a very effective and convenient method for water purification. Iodine destroys bacteria, viruses and cysts, and its action is dependent on its concentration, the water temperature and duration of contact. Thus, a concentration of 8 mgs per litre at 20 degrees centigrade, will destroy all pathogens if left for 10 minutes. Lower concentrations and lower water temperatures require a longer duration of action.
Various preparations of iodine are available, including tincture of iodine, iodine crystals and tablets. Manufacturers instructions should be followed in each case. With tincture of iodine, adequate levels are normally achieved by using 4 drops to 1 litre of water or one drop to a glass. As with all halogens it is less effective against cryptosporidia.
Iodine has been used safely for periods of several months, however it is not known whether there are adverse effects associated with longer term use. Those with a history of thyroid disease or iodine allergy, the pregnant and the very young may be advised against using iodine for water purification.
The taste of iodine can be largely removed by neutralising the iodine, after it has had time to work, with dissolvable vitamin C tablets, lime or lemon juice. It should be noted that this also stops the disinfectant action, so care should be taken to prevent recontamination of water. Iodine has now been successfully replaced by Chlorine Dioxide
Chlorine dioxide tablets take 30 minutes to kill a protozoa called giardia and bacteria but can take up to 4 hours (or longer) if your water is turbid with suspended particles or very cold. In such cases, boiling for a few minutes may be the only way to quickly purify it without a filter. Chlorine dioxide also kills a second common protozoa called cryptosporidium, but requires 4 hours of contact.
Cryptosporidium is widely distributed in the ecosystem and not waiting the 4 hours required to kill it is a risk. One way to mitigate this risk is to filter out cryptosporidium using a filter such as a MSR Sweetwater Microfilter Chlorine and silver When used correctly they destroy most bacteria (e.g. V.cholerae), but are less effective for viruses and cysts (e.g. hepatitis A virus, giardia and amoebic cysts, cryptosporidia).
Chlorine alone is readily inactivated by organic matter and its action varies with pH. However if used in combination with Phosphoric acid in combination (e.g. Aquamira) it is more effective and this combination will destroy both giardia and cryptosporidia.
A wide variety of filters are available. Some versions have cores which can be replaced. Filters remove sand, clay and other matter as well as organisms by means of small pore size, membranes, adsorption, exchange resins and osmosis. They effectively remove bacteria and parasites but not viruses. Good filters are effective against cryptosporidia and giardia. Due to the inability to remove viruses, filtered water must also be chemically treated or boiled.
Some modern filters incorporate a method of chemical disinfection to increase their effectiveness. This is usually achieved by passing water through iodine exchange resins. When negatively charged contaminants contact the iodine resin, iodine is instantly released so killing the microorganisms without large quantities of iodine being in solution. Such filters should be replaced after a specified volume of water has been treated, although this could sometimes be difficult to keep track of.
Q: Why do I need to treat water in wilderness areas?
A: Regardless of how pure water may look, any water source on the planet could be tainted with microscopic waterborne pathogens —invisible-to-the-eye, disease-causing pests that, if ingested, could cause all sorts of tumult in your tummy. Severe diarrhea, cramps, vomiting and fever are the symptoms. Serious infections can last for weeks.
Recent research, though, suggests that wilderness water at higher elevations is much cleaner than previously believed. Some experts argue that treating backcountry water is often a waste of effort and that the blame for intestinal infections is more often traceable to preexisting conditions and lax sanitation, particularly unwashed hands.
Q: What's in wilderness water that can affect me?
A: Three groups of waterborne critters are most commonly linked to water-related illness:
Q: How do they get in the water?
A: Protozoa (parasites) and viruses are present in surface water that has become contaminated by animal or human waste, principally feces. (That's polite talk for poop.) Bacteria, including many beneficial bacteria, naturally occur in water. Because water keeps their membranes moist, bacteria thrive in water. Water contaminated by faecal material often results in a population of harmful bacteria such as E. coli. When soap is introduced to water, it creates a supply of nutrients of that can sustain pathogens or cause algae blooms. Soap residue generated by careless humans is a growing problem in backcountry water.
Q: Are these bugs everywhere?
A: Potentially, yes. Yet some studies suggest that many remote waterways and springs in less-traveled, high-elevation backcountry regions are rarely contaminated.
Q: How can a person know if a water source is tainted?
A: Unless you are a scientist with testing materials, it's guesswork. Over time, though, experienced wilderness travelers can learn to make reasonably educated evaluations. Yet even the savviest outdoor explorer will choose to carry some method of water treatment for the inevitable situations where water is viewed with suspicion. Thus Trailblazer Outdoors recommends always carrying some method of water treatment when exploring the backcountry.