Clear water isn't necessarily safe water. Microorganisms like Giardia, Cryptosporidium, and E. coli can lurk in the purest-looking mountain streams. Here is an analysis of the three primary methods for making wild water safe to drink.
1. Boiling
Pros: Failsafe. Requires no special gear other than a container and fire.
Cons: Time-consuming, uses fuel, and water needs to cool.
The CDC recommends bringing water to a rolling boil for 1 minute (or 3 minutes at elevations above 6,500 feet) to kill all pathogens, including viruses, bacteria, and protozoa.
2. Chemical Treatment
Pros: Lightweight, cheap, and effective against viruses and bacteria.
Cons: Takes time (30 min to 4 hours), bad taste, and some chemicals (like Iodine) don't kill Cryptosporidium efficiently.
Chlorine Dioxide tablets or drops are the gold standard for chemical treatment, as they are safer and more effective than traditional iodine.
3. Mechanical Filtration
Pros: Instant clean water, no chemical taste.
Cons: Can clog, freeze, and expensive to buy.
Filters with a pore size of 0.1 or 0.2 microns are standard. They remove bacteria and protozoa but NOT viruses (which are too small). In North America, this is usually sufficient, but in developing nations, a purifier (often combining filtration and chemical/UV) is needed.
Recommendation
For a robust survival kit, carry a cleanable mechanical filter (like a Sawyer Squeeze) for convenience, and back it up with a metal canteen for boiling. Redundancy keeps you alive.