Purification Techniques Long gone are the days when you could drop your exhausted body to the ground beside a sparkling flow of wilderness water and plunge your face into the cold rush for a drink. Pathogens – including chemical pollutants, protozoa and larger parasites, bacteria and viruses – inhabit most of the world’s water to some degree, and unless you’re willing to risk gut-ripping misery, it is of critical importance to carry some means of water disinfection on wilderness trips.

There are three basic tried and tested ways to make sure your wilderness water is safely disinfected: Boiling, Halogenation, and Filtration. You should pick the one that best suits your needs and is appropriate to your activity.

Boiling
The rule is very simple: Once the water is hot enough to produce one rolling bubble, it is free of organisms that will cause illness, worldwide and up to at least 19,000 feet above sea level. The reason: All of the time it takes to bring water to a boil works toward the death of organisms in the water. By the time water reaches the boiling point it’s safe. Giardia lamblia cysts, for instance, die at approximately 122 degrees F (50 degrees C). If you want to "feel" safer, let the water roll around at a boil for a couple of minutes. Boiling is cheap – the only cost is fuel – and effective, but it consumes time, and it’s inconvenient if you run out of water on the trail. Boiling will NOT neutralize chemical pollutants.

Halogenation
As for chemicals that kill water-borne pathogens, both chlorine and the iodine in Potable Aqua have been proven relatively effective, given enough of the chemical and enough time. Halogenation is affected by water temperature (the warmer the better), the pH of the water, and the turbidity of the water. For best results strain out particles by pouring water through a clean T-shirt or bandana before adding Potable Aqua. Halogens are generally more convenient and faster than boiling the water (when you consider lighting the stove or building the fire), but they cost a bit more and can’t be guaranteed to work as well as other means of water disinfection.
Chlorine and iodine, for instance, have not been proven fatal to Cryptosporidium. Halogens also tend to leave the water tasting crummy, a phenomenon reversible by adding flavoring (such as energy drink powders), or, if using iodine, an iodine-taste-removing product, such as Potable Aqua Plus, after the disinfection process has been completed. If you add anything to the water prior to complete disinfection, the added substances may disrupt the disinfection process. A simple rule is: Follow the directions on the label.

Filtration
Water filters physically strain out some of the organisms and contaminants in water that could cause disease. Structurally, there are two basic kinds of filters:

1. Surface or membrane filters are thin perforated sheets that block impurities;
2. Depth filters are made of thick and porous materials that trap impurities as the water is forced through.
   

The effectiveness of filters varies greatly from one that removes only relatively large particles, such as Giardia lamblia, to one that removes virtually everything removable. Viruses are too small to be filtered out, but some filters kill viruses with iodine from resins on the filter as the water passes through. Mechanically there are also two basic types:

1. Pump-feed filters that require manual force to push the water through the filter.
2. Gravity-feed filters that just hang there while water drips via gravity through the system.
   

Filtered water looks "clean," but the purity of the water depends on the specific filter. Read the claims of a filter carefully before your purchase. They are available in a wide variety of costs, shapes and sizes. Filtration, in general, costs more but offers the quickest route to safe water.