Although the typical traveler going to the developing world can access safe purchased or prepared water, the availability of pure water cannot always be guaranteed. In this situation, travelers should be prepared to treat water by 1 or more of the following methods.
High temperatures kill most germs quickly. Boiling is always a reliable method for killing common intestinal pathogens found in water. Urban travelers may choose an immersion coil for boiling water (a plug adapter and current converter might be necessary). Any water brought to a boil should be adequately disinfected, but boiling for 1 minute (from the time the water begins to bubble) allows for a margin of safety. Although the boiling point decreases at higher altitudes, at common travel elevations, the water temperature remains adequate to kill intestinal pathogens.
If boiling water is not possible, chemical disinfection is an alternative. Most (but not all) diarrhea pathogens are susceptible to iodine, which can be used to disinfect water, leafy vegetables, and fruits. Add 5 drops of 2% iodine to 1 L (33.8 oz) of water and let stand for 30 minutes. Tetraglycine hydroperiodide tablets (e.g., Globaline, Potable-Aqua, Coghlan's) are available from pharmacies and sporting goods stores. Follow the manufacturer's instructions. In many countries, potassium permanganate (iodine containing) solutions (always purple in color) are readily available and can be used according to instructions to disinfect fruits and vegetables.
Travelers who have thyroid problems or iodine allergies or who are pregnant should not use iodine for water purification. Limit the use of iodine to a few weeks to avoid its effect on the thyroid from long-term use.
For those travelers who wish to avoid the taste and smell of iodine in their disinfected water, vitamin C (ascorbic acid) can be added to the water after the iodine has been in contact with the water for 30 minutes or more. Add about 25 mg of vitamin C to 1 L (33.8 oz) of water and shake briefly to eliminate the iodine taste and odor.
Chlorine (e.g., sodium hypochlorite) can also be used for water purification. Given adequate concentrations and contact time, chlorine and iodine have similar effectiveness against bacteria and viruses. However, chlorine's germicidal activity varies greatly with temperature and other factors and therefore is less reliable than iodine.
Portable filters are not guaranteed to make drinking water safe; most authorities make no recommendation regarding their use due to lack of independent verification of efficacy. However, filters may be helpful (when used with chemical disinfection) in situations where boiling all drinking water is not practical. A good quality filter with a pore size of 0.1 to 0.4 microns and impregnated with iodine will effectively remove cysts, bacteria, and killed viruses. Nonimpregnated filters may not adequately remove viruses, which is a major concern with high levels of fecal contamination; the water should then be chemically treated as well.
Filters rapidly clog if the source water is cloudy or contains large amounts of sediment. Filtration effectiveness can be improved by first removing suspended particles through the process of coagulation-flocculation (clumping of smaller particles into larger particles) with alum. This process clumps the suspended particulates and allows them to settle, allowing for easy removal of the sediment by pouring the water through a fine cloth or coffee filter.
Ultraviolet (UV) light can kill bacteria, viruses, and protozoan oocysts in water. Battery-operated, portable units that deliver UV doses have become available and may be useful for disinfecting small quantities of clear water. This technique is less effective for cloudy or turbid water.