Preventing Illness while Camping, Hiking, and Traveling

Although water from lakes, streams, and rivers may look clear and refreshing while out hiking or camping, it can still be contaminated with viruses, parasites, and bacteria that can make people sick. Campers or hikers who drink untreated or inappropriately treated water from lakes, streams, or rivers are at an increased risk of becoming ill with waterborne diseases.

Several methods can be used to treat drinking water. Boiling is the most effective way to remove harmful microorganisms from untreated or poorly treated water. Filtration followed by disinfection is also very effective. Always bring at least one backup water treatment method in case one fails.

On this page:
Boiling
Filtration & disinfection
Other Methods
More information

Boiling

Boiling water is the most effective way to remove harmful microorganisms from untreated water sources.

• Bring water to a rolling boil. Continue to boil for 1 minute or, to conserve fuel, remove from heat but keep the pot covered for several minutes.
• Muddy water should stand for a while to allow silt and debris to settle. Pour off the clear water on top for boiling.

Filtration & disinfection

Used together, filtration followed by disinfection has a very high effectiveness in removing all microorganisms from water.

Filtration

Filters can be effective at removing microorganisms from the water depending on the filter’s pore size and the microorganism’s size and charge. Always follow manufacturer instructions.

• Filters with an absolute pore size ≤1 micron (NSF Standard 53 or 58) have a high effectiveness in removing Giardia and Cryptosporidium.
• Filters with an absolute pore size ≤0.3 microns have a moderate effectiveness in removing bacteria.
• Only filters that contain a chemical disinfectant matrix will be effective against some viruses.
• Poor filter maintenance or failure to replace the filter cartridge as recommended by the manufacturer can cause a filter to fail.

Disinfection

Contact time, disinfectant concentration, and water temperature, turbidity, and pH along with other factors impact the effectiveness of chemical disinfection. Always follow manufacturer instructions. 

• Chlorine dioxide, chlorine, and iodine have a high effectiveness in killing bacteria and viruses.
• Chlorine and iodine have a low effectiveness in killing Giardia and are not effective in killing Cryptosporidium.
• Chlorine dioxide has a high effectiveness in killing Giardia and a low to moderate effectiveness in killing Cryptosporidium.
• Water that has been disinfected with iodine is not recommended for pregnant women, people with thyroid problems, those with known sensitivity to iodine, or continuous use for more than a few weeks at a time.

Other methods

Ultraviolet (UV) light might be an effective pathogen reduction method in the backcountry, but there is a lack of independent testing data on individual systems. UV light requires pre-filtering because it needs low water turbidity (cloudiness) to work effectively. Correct power delivery, water agitation, and contact times are also required for maximum pathogen reduction.

Harmful Algal Blooms

Harmful Algal Blooms (HABs) look like pea soup or spilled green paint and can produce cyanotoxins that can make people and animals ill. Water treatment devices designed for the backcountry are not able to destroy or remove the toxins. Boiling will not remove toxins and can increase toxin levels. Do not drink water from a water body with a suspected or posted harmful algal bloom. 

More about preventing illness during camping, hiking, and travel

• Water Treatment in the Backcountry (PDF)
  Information about the effectiveness of different water treatment methods to guide individuals who plan to use backcountry water for drinking.
   
• Make Your Water Safe (PDF)
  Poster to encourage and educate users of backcountry water on proper safety measures. 
   
• CDC: A Guide to Water Treatment While Hiking, Camping, and Traveling (PDF)
  Guidance about what to look for to ensure a water filter was designed to remove Cryptosporidium. Filters that can remove Cryptosporidium cysts can also remove Giardia cysts. 
   
• CDC: Guide to Drinking Water Treatment and Sanitation for Backcountry & Travel Use
  Guide for individuals intending to use untreated or poorly treated water for drinking.