1. Heat - Boiling water is effective for disinfection at any altitude (below 18,000 feet) likely to be attained by a wilderness enthusiast. The time required to heat the water to boiling contributes to the disinfection process. To provide a wide margin of safety, one can boil the water for 3 minutes.
2. Filtration - Filter the water through a category three (as set for purification by the Environmental Protection Agency) water treatment device. Filters with pore sizes of 0.1 to 0.4 micron are readily available. These have pores small enough to filter out Giardia cysts and some bacteria, but not viruses (which are 0.03 micron in diameter).
   • If your filter doesn't have a "prefilter" (nylon mesh or screen) to remove large particles, first pour the water through filter paper, fine cheesecloth or a bandana. This helps to keep your expensive water filter from clogging up and allows it to work more efficiently, improving the appearance and taste of the water.
3. Chemical disinfection - Halogens, such as iodine and chlorine, are effective chemical disinfectants. The rate at which they kill microorganisms depends upon concentration and time.
   • Double the contact time if 1/2 the concentration of halogen is present.
   • Decreased (cold) water temperature or cloudy (more organic material) water requires a longer contact time or higher halogen concentration.
   • Halogens can create an unpleasant taste and may lose effectiveness after prolonged exposure to moisture, heat, or air. To improve taste, use a lower concentration of halogen (for a longer contact time) or add powdered drink mix/flavoring after the water has been disinfected.

A pregnant woman or a person with thyroid disease or iodine allergy should consult a physician before using any iodine compound for water disinfection.

It is absolutely essential to keep the iodine crystals out of the hands of children.