Water Precautions

In developed countries, clean drinking water is available out of the tap, and breakdowns in the system are rare. Developing countries, however, don't always have the resources needed to ensure a pure water supply; consequently, tap water is not safe to drink. Even if the local population can drink the water, travelers should not assume that they can. Local residents have built up some immunity to organisms in the water, but visitors have not. As a result, tap water can make travelers ill.

When traveling through areas with less than adequate sanitation or with water sources of unknown purity, travelers can reduce the chance of illness by observing the following precautions.

Use sealed bottled water or chemically treated, filtered, or boiled water for drinking and for brushing teeth. Drink beverages made only with boiled water whenever possible (such as hot tea and coffee). Any water brought to a boil at sea level is safe to drink.

Drink canned, boxed, or commercially bottled carbonated water and drinks. International brands are safest. Beware of unsealed containers that may have been refilled. Beer and wine are safe to drink; however, alcohol added to other beverages does not render the beverages safe. Carry safe water if going out for the day in an area where availability of safe water is not assured. Don't assume that chlorinated water is safe; chlorination does not destroy all the organisms that can cause illness.

Continue to breastfeed nursing infants because nursing is the safest food source for these infants. If formula is used, prepare with boiled water and sterilized containers.

Avoid tap water or anything mixed with tap water and don't rinse toothbrushes in tap water. Don't drink fruit juice unless it comes directly from a sealed container; otherwise, it may have been diluted with tap water. Don't drink from wet cans or bottles; the water on them may be contaminated. Dry wet cans/bottles before opening and clean all surfaces that will have contact with the mouth. Don't use ice unless it is made from boiled, bottled, or purified water. Freezing does not kill the organisms that cause diarrhea.

Purify water if one of these options is not available. Decide which method to use for water purification and bring along the appropriate equipment.

Treating Water

Drinking Water Treatment Methods' Effectiveness for Different Pathogens
Germ Heat/Boiling Chemical Disinfection Filtration UV Light in Clear Water Combined Filtration and Disinfection
Chlorine or Iodine Chlorine Dioxide
Bacteria ++++ +++ +++ ++ +++ ++++
Viruses ++++ +++ +++ - +++ +++
Parasites (e.g., Giardia) ++++ + to ++ +++ +++ +++ ++++
Parasites (e.g., Cryptosporidium) ++++ - + to ++ +++ +++ ++++
- not effective; + low effectiveness; ++ moderate effectiveness; +++ high effectiveness; ++++ very high effectiveness


High temperatures kill most pathogens quickly. Boiling is always a reliable method for killing all of the common intestinal pathogens 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 is considered adequately disinfected but continued 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 germs. Boiling does not prevent recontamination during storage.

Chemical Disinfection

If boiling water is not possible, chemical disinfection with chlorine compounds, chlorine dioxide, or iodine is an alternative and these products are commonly available at pharmacies and sporting goods stores. Most (but not all) diarrhea pathogens are susceptible to being killed by these compounds given adequate concentrations and contact time. Because not all parasites are inactivated with chemical disinfection, preceding it with filtration will provide optimal protection for all situations. Iodine can also be used to disinfect leafy vegetables and fruits.

Travelers who have thyroid problems or iodine allergies or who are pregnant should not use iodine for water purification. The use of iodine should be limited to a few weeks to avoid its effect on the thyroid from long-term use.

Both chlorine and iodine impart a taste and odor to the water, but both can be easily removed; once the treated water has sat for at least 30 minutes, filter the water through activated charcoal or add a 25 mg tablet of vitamin C or 5 to 10 drops of 3% hydrogen peroxide per liter of treated water and shake briefly.

Chemical Disinfection Doses
Disinfection Method Amount to Add to 1 L (1 qt) of Water Time to Disinfection
2% Iodine solution 0.2 mL (5 drops) 30 min
10% Povidone-iodine solution 0.35 mL (8 drops) 30 min
Iodine tablets (e.g., tetragycline hydroperiodide) 1/2 tablet 30 min
Sodium hypochlorite (household bleach 5%) 1 drop 30 min
Chlorine dioxide 1 tablet 4 hrs (away from sunlight)

Portable Filters

Portable filters are not guaranteed to make drinking water safe but may improve the taste and appearance of the water; most authorities make no recommendation regarding their use because of insufficient independent verification of efficacy.

However, in areas where boiling all drinking water is not practical, a good quality filter with a pore size of 0.1 to 0.4 microns will effectively remove cysts and bacteria but may not adequately remove viruses, which is a major concern with high levels of fecal contamination. The filtered water should then be treated chemically as well.

Ultraviolet (UV) Light

UV light can kill all waterborne bacteria, viruses, and parasites, but the water must be clear and free of particles to allow the UV light to reach all the organisms. Battery-operated, portable units that deliver UV doses have become available and may be useful for disinfecting small quantities of clear (not cloudy or turbid) water. UV treatment does not improve taste, smell, or appearance of the water.

Solar Disinfection

Solar disinfection (SODIS) may be used in austere emergency situations to disinfect relatively clear water. Place clean, clear plastic PET or glass bottles (up to 3 L [3 qt] volume) filled with water on a dark surface in the sun for at least 6 hours (2 days if cloudy) and agitate periodically. If unable to read large text through the bottle of water (looking at the bottom of the bottle through the neck at the top), filtration should be performed before SODIS is used. Treated water should be kept in and either drunk directly from the bottle or poured into a cup immediately before drinking to prevent recontamination.