Outdoor Life Online Editor

About 10 years ago I was fishing on the west slope of the Rockies with a buddy of mine. The water was so clean you could smell the freshness.

In the heat of the day my friend took a long drink right from the stream. I warned him not to, but he ignored me. Later, in deference to our friendship, I said nothing as he spent a day and a night in the sweaty twists and turns of “beaver fever,” caused by the cysts of the protozoan Giardia, which can be found just about anywhere.

Water gets polluted by lots of things: chemicals, heavy metals, bacteria and viruses. Even crystalline brook water that looks as pure as the day the earth was formed might harbor the worst kinds of impurities. You can’t tell by looking, smelling or tasting. So you must purify every drop you drink.

There are three methods to cleanse water-thermal, chemical and by filtration. Sometimes it takes a combination of the three to really do the job right. But you should at least be equipped at all times for two of these methods.

Thermal Purification
Boiling is probably the easiest, and oldest, way to create sanitary drinking water in a wilderness situation. It’s not perfect, but in most cases it is sufficient.

Bring a pot of water to a rolling boil and keep it there for one minute at sea level and one additional minute for every 1,000 feet of elevation above sea level. If you don’t know your elevation, boil for 10 minutes just to be sure. This method will kill parasites, bacteria and viruses and is considered the most reliable method of purifying drinking water by the Centers for Disease Control (CDC). It won’t, however, eliminate chemical or heavy metal toxicity.

This method can render water “flat” tasting, but that’s of little concern. When you’re dehydrated, any clean water is good water.

Chemical Purification
Chemical purification of water is accomplished by the use of iodine or chlorine, both of which are toxic substances. And that’s the whole point-to poison the undesirable creatures that live in the water while using a dosage that is small enough to be safe for human consumption. Virtually every municipality in the country uses chlorine water treatment.

Iodine and chlorine water purification products are available from most outdoors stores in small, easily packable bottles. The cost is pretty low-around $12 for a bottle that can treat 100 liters of water. Follow the manufacturer’s directions on dosage, but keep in mind that both iodine and chlorine lose their effectiveness as they age.

Ingesting either iodine or chlorine poses a slight hazard to people who are highly sensitive or even allergic to these substances, especially iodine. The trouble is, there is no way to know beforehand unless your doctor has performed an allergy test or you’ve had direct contact with either iodine or chlorine and have had a reaction. People with active thyroid disease and pregnant women also should not ingest iodine.

There are some outstanding backpackable filtration devices available that can screen out bacteria, parasites and harmful chemicals, but there are also “junk” filters on the market that don’t do anything more than remove foul odor and taste. Backpackable filters look like a kind of canister, in which the filter element resides. They weigh about a pound and fit in a carrying bag. I keep one in my survival pack (“Save Your Butt,” April 2002). It’s a little bulky, but well worth the space.

Among the better filters are two types worthy of consideration: a membrane filter and a depth-type filter.

A membrane filter utilizes a porous membrane that permits water to pass through but stops particulates larger than the size of the pores. These filters clog quickly but are easy to clean.

A depth-type filter utilizes an element such as a ceramic block that is porous enough to force water through yet dense enough to capture the bad stuff. The element can be cleaned by scrubbing or back-flushing when it becomes clogged. You must be careful not to break it.

If a carbon element is included with the filter, the system will be able to remove some chemicals and heavy metals, as well as improve the flavor and aroma of the water. Filters are available with a wide range of pore sizes, resulting in varying effectiveness against microbes. Filters with pore sizes in the 0.1 to 0.3 micron range can remove bacteria and protozoan cysts but will let viruses slide right through.

Beyond Filtering
Even though your high-dollar sub- micron filter is rated to eliminate such things as bacteria, Giardia and Cryptosporidium (a protozoan responsible for cryptosporidiosis, an illness similar to beaver fever), viruses are so small they will squeeze through the pores of the tiniest filter element. The only way to eliminate viruses is through thermal (boiling) or chemical means.

To be able to eliminate viruses without boiling, I carry the SweetWater Guardian Purifier System. It’s a compact depth-type filter, but the actual purifying is done by a chlorine-based liquid called ViralStop. I filter the water, add five drops of ViralStop for every liter of water and wait five minutes before drinking. The manufacturer claims almost 100 percent elimination of viruses, bacteria and parasites. Another such unit is the Pur Water Filter, which I also own.

The SweetWater and the Pur cost around $80 each, and replacement filter cartridges run about $30 each.

If cost is a consideration, go back to the basics of boiling water. The essential ability to make fire anywhere, anytime, doesn’t just apply to keeping warm and drying off. Dehydration can kill you. Avoiding it depends greatly on your ability to make fire. It’s the simplest and most effective way to create drinkable water.