Water Purification 

This is about water purification in the mountain. I am not a doctor, I'm not a biologist. Use this information at your won risk.

A mountain climber needs to drink 4-5 liters of water a day. For a multi-day climb, it is not viable to bring all the water from home. The solution is to drink water from melted snow or from streams, which can be contaminated. This article discusses the methods to purify water so that it becomes suitable for drinking.

When drinking unreliable water, we have to worry about:

• Microorganisms such as viruses and bacteria. They can cause diseases ranging from simple diarheea to hepatites. They can be eliminated by chemical treatment (clorine, iodine) or by boiling water for a few minutes
  
• Cysts. Protozoa such as giardia and cryptosporidia when exposed to adverse conditions form a hard shell (cyst) and go into a hibernation state until it is liberated in our digestive system. They can cause diseases that are hard to diagnose and can become chronic conditions. Cysts can be eliminated by microfiltering (<1u filters) or boiling. Giardia can also be eliminated with iodine (but not clorine). Cryptosporidia is resistant to chemical treatment.
  
• Dirty, tastes, odors. In addition to being indication of polluted water those characteristics make drinking water unpleasant. Filtering is the best way to get rid of those.

Boiling water for a few minutes (longer at high altitude) is the safest method of purification, but that may take so much time and energy to make it non practical for all the drinking water.

In the US mountains, cysts (giardia and cryptosporidia) are probably the major concern. The risk of bacterial and viral (hepatite and the like) infection in cold waters is very low. So, many people rely solely on a microfilter. I personally like filtering, but tent to be skeptical about its ability to remove all the undesirable things in the water.

If you are to use only a chemical purification method, it would be iodine. It is effective, cheap, lightweight and foolproof. It kills almost everything (including Giardia), but the effectiveness against Cryptosporidia is partial at best. Iodine leaves the water with color and bad taste, problem that can be minimized with the addition of vitamin C tablets (and/or gatorade). If you are allergic to shellfish, you will most likely be allergic to iodine. Pregnant women and people with serious tireoid problems should also avoid iodine.

The solution I adopt is to use a microfilter, followed by purification with iodine or clorine for drinking water. For cooking, I simply boil the water.