All backcountry water sources, including fast-flowing, glacier-fed streams can be contaminated by passing birds, animals, or humans. The cleaner water is to start with, the more effective any treatment method will be. If possible, avoid still water, and use the clearest water you can. If you must use cloudy or muddy water, let it settle in a pot or bucket, and siphon off the clear water to treat it.
Waterborne pathogens (disease-causing micro-organisms) of most concern:
- Protozoa include cryptosporidium and giardia (the cause of giardiasis or “beaver fever”). Protozoa are increasingly widespread in North America. They are larger than one micron (one-millionth of a metre.)
- Bacteria exist in water all over the world. Most are harmless, but some cause sicknesses such as diarrhea and dysentery. Most bacteria are about 1.0 micron in size, although some, such as the disease-causing campylobacter, can be as small as 0.2 microns.
- Viruses cause hepatitis, polio, and other diseases. They can be present in any water contaminated by human waste. Most viruses are in the 0.1 micron size range, but they can be as small as 0.002 microns.
|Treatment methods compared||protozoa||bacteria||viruses||particulate|
|chlorine dioxide/mixed oxidants||yes||yes||yes||no|
|0.5mi filter and pre-filter||yes||most||no||yes|
|0.2mi filter and pre-filter||yes||yes||no||yes|
|0.1mi filter and iodine/chlorine||yes||yes||yes||yes|
|ultravioliet (UV) light||yes||yes||yes||no|
|UV light and pre-filter||yes||yes||yes||yes|
Enough heat will destroy all pathogens, but it’s not a popular method as it consumes time and fuel, and boiled water has a flat taste. So, except for cooking water, most people treat their water with filters, chemicals, or both.
- Recommended times range from 3 to 10 minutes.
- Higher elevations require slightly longer boil times.
These don’t require any pumping to use, but they do require time to act – from a few minutes to several hours, depending on how cold or dirty the water is, and which pathogens you want protection against. Chemicals are effective against bacteria and viruses. But some protozoa, including some cryptosporidium, are resistant.
Chemicals are good for short-term use: a few days or a few weeks. For many, the health risk associated with small amounts of exposure to chemicals is outweighed by the benefit of protection against pathogens. But pregnant women, young children, or anyone iwith a pre-existing health problems, this may not be true. Best to consult your doctor before using chemical treatments.
- Chlorine kills many of the micro-organisms that help you digest food, resulting in digestive trouble. In water, chlorine also forms some by-products that are suspected carcinogens.
- Iodine comes in easy-to-use drops or tablets, though many people don’t like the taste and odour it adds to the water.
- Chlorine dioxide is unstable, so you prepare it in the field by mixing two component chemicals. Since the active ingredients in chlorine dioxide break down quickly, it usually won’t kill beneficial micro-organisms in your digestive system. It doesn’t leave any unpleasant taste or odour in your treated water.
Filters strain out pathogens when water is forced through them. They remove protozoa and some larger bacteria, and at 0.2 micron, also remove smaller bacteria such as campylobacter. Viruses are many times smaller than bacteria, so most filters cannot remove them.
- Filters can fail or be damaged by impact. Many people carry compact water treatment tablets as a back-up.
- Great where viruses are not a concern, or for occasional users, small groups, and short trips.
- For protection against viruses, you can treat water with iodine then filter it. A filter with a carbon stage can remove between 90 to 98% of iodine.
These have one or more filter stages that trap larger pathogens, together with an iodine resin or another element that inactivates viruses.
- High-end purifiers do not introduce chemicals into the water.
- Economical over the long term. Suited to frequent users, extended trips, and larger groups.
UV light purifiers
Portable devices designed to treat 0.5 or 1L of water at a time. By beaming UV light through water, they damage the DNA of microbes, pathogens and viruses. It’s the same tech used in commercial bottling plants and municipal water systems.
- They avoid the taste, health concerns, and waiting times of chemical treatments.
- Don’t require pumping, and don’t need to be dissembled and dried when you return home.
- Cloudy water must be filtered before you use UV.
- Most use batteries, so you’ll need to carry spared or a solar re-charging system.
Filters should be taken apart and left to air-dry to help prevent mildew and bacteria growth. They can be cleaned many times with a brush before needing to be replaced, but clean them only when necessary to prolong their life.
Silty water (associated with glacial regions) clogs filters with debris and makes the pumps more difficult to operate. To make pumping easier, let silt settle for an hour or two before pumping the water.
Usually, the lower the initial cost for a treatment method, the higher the cost of each litre treated.
- If you camp occasionally and in a small group, a moderately priced filter with a semi-disposable cartridge, combined with a small chlorine dioxide kit, may be fine.
- If you camp frequently, or with a large group, it may be more economical in the long run to buy a more expensive filter.
- Inexpensive filters clean a few dozen to a few hundred litres. A high-end filter might clean thousands of litres.
- A UV purifier with rechargeable batteries might treat 3,000-8,000 litres.