Clean Water Information


 OBTAINING WATER - water from a polluted source may be contaminated with organic material. Cloudy water also requires more time and more chemicals to disinfect, especially if it is cold. Chlorine, (Clorox) in particular is neutralized by organic material.


  • Turbid water - let stand undisturbed for several hours. Pour off the upper clear portion and treat.
  • Organic impurities may not settle out with gravity alone. Add a pinch of alum (available over the counter in drug stores) and mix. Clumping of suspended organic impurities will occur, and the clumped particles will settle to the bottom of the container. Pour off the upper clear portion and treat.
  • Pour the water through a course paper filter, commercial filter paper, fine cloth, or a canvas filter bag to remove the sediment more rapidly. Pour off the upper clear portion and treat.
  • Ceramic and glass fiber filters that filter bacteria and parasites also filter out organic material, but clogging will occur. You can either follow any of the above suggestions first, or add a sediment filter on the inlet hose. Ceramic filters can be cleaned many more times than glass fiber filters. 


Boiling - Water that is brought just to a boil and then allowed to cool is safe to consume. Boiling water for 10 to 20 minutes, even at high altitudes, is unnecessary and wastes time and fuel. Some people even question the need to boil water at all-they just "pasteurize" it by heating it for a period of time at a sub-boiling temperature. To kill cholera germs, for example, boiling is not necessary. Heating contaminated water to 144'F (62'C) for 10 minutes is sufficient to eliminate completely all strains of this bacterium.

NOTE: Boiling water at 10,000 feet raises its temperature to an adequate 194 F (900C).

Advantages of boiling-Boiling water completely eliminates bacteria, cysts of parasites (amoebic, giardia, cryptosporidia), worm larvae that cause schistosorniasis, and viruses (the cause of hepatitis, polio, and viral gastroenteritis). Briefly boiling water won't eliminate the spores of certain bacteria; hence, the water can't be considered absolutely sterile. However, bacterial spores, should they be in the water, don't cause intestinal illness and can be consumed without harm.

Boiling water is not easy. Heating the water is time-consuming, often inconvenient, and may require you to carry a source of fuel with you. Boiling is usually most easily done at a base camp, not on the trail.

Iodine or chlorine - Under proper conditions, both iodine and chlorine are excellent water disinfectants for eliminating bacteria and viruses; they are less effective against parasites, especially when contact time is brief and/or the water is cloudy and cold. Take the time to remove organic material.

Iodine has been used to disinfect water since the turn of the century and is still the lightest, cheapest, simplest method of water purification. U.S. Army studies have demonstrated that under field conditions (dirty, cold water; a 10-minute contact time) iodine completely kills bacteria, parasites, viruses, and worm larvae. However, that was before Cryptosporidium came along. The one serious drawback to iodine is that it does not kill crypto. Unlike all other microorganisms (bacteria, viruses, giardia) which iodine effectively eliminates, cryptosporidium is a super-cyst with an extremely durable shell. The only way to eliminate it is by either boiling or filtering the water.

Potable Aqua is the most popular brand of iodine and is available in our stores. Dissolve one tablet in a liter of water and wait 20-30 minutes. If the water is cold and cloudy, use two tablets and wait at least 30 minutes. PA Plus adds the ability to remove any iodine taste after treatment.

Advantages-Tablets usually have a long shelf life and they won't stain your pack or clothing if spilled.

Disadvantage: Many people object to the taste. Travelers with thyroid disease should avoid any prolonged use of iodine. Medical authorities advise pregnant women not to drink excessive amounts of iodine-containing water because of potential adverse effects on fetal thyroid gland development. Careful studies have not been done, and pregnant women should use iodine if it is the only alternative to drinking contaminated water.

Liquid chlorine bleach (4% to 6% Clorox) - Household bleach is easily available and cheap, but doesn't kill crypto and may not kill giardia or cyclospora cysts, especially if the water is cloudy or cold. Add 2 to 3 drops of chlorine bleach to each quart of water if it is clear and from the tap; add 4 to 6 drops if the water is cloudy or not from the tap. Wait at least 30 minutes before drinking.

Note: Take the time to remove organic material before treatment.

Water Filters and Purification Devices - A filter's basic task is to remove organisms and particles larger than a specified size from water. This mission isn't so easy, given the small size and variety of pathogenic microorganisms that can be encountered, and a variety of filters have therefore evolved: ceramic filters, depth filters, and surface filters. These filters all come with a rating of their pore size, which determines what size particles can be physically removed. Pore sizes are measured in microns, and the period at the end of this sentence is about 600 microns across. In commercial terms, the most important number is the "absolute" pore size rating, which means the filter element will pass no particle above a certain size. These absolute ratings are much more meaningful than the vaguely defined "nominal" ratings that filter manufacturers sometimes use.

To strain out common parasites, such as giardia, a pore size no larger than 4.0 microns is necessary. (Protozoa range in size from 5 to 15 microns.) For bacteria, (which range in size from 0.2 microns to 10 microns), an absolute pore size of 0.2 microns is desirable. Unfortunately, a filter this fine is subject to rapid clogging and will require a pre-filter and more frequent cleaning. Because viruses can be as small as 0.0004 microns, no field device that relies entirely on filtration will remove them.

Some filters have been designed to filter out only larger organisms such as parasites and worm larvae. These devices are sold primarily to backpackers who want to avoid giardiasis. Many international travelers, however, now opt for complete protection and choose a unit that will also remove bacteria and viruses. Because a filter alone won't take out viruses, travelers treat water with iodine and proceed to use the filter as their final purification process.

Choosing a filter/purification device - Beside removal of microorganisms, you need to consider the following factors in choosing one of these devices - (1) rated output in per minute, (2) life of filter element before replacement, (3) dimensions and weight of unit with accessories, (4) and cost, of the device and of the replacement filters. You also may want to know if the unit removes organic chemicals, such as pesticides, and improves the taste of the water. An activated charcoal filter is usually required for these functions.

Credit: Backpacker Magazine. March 1994 and Travel health Guide 1998