Bad Backcountry Water: Giardia, Crypto, Bacteria, Viruses

You can find a lot of nasty things in the water when backpacking--water filtering systems are meant to eliminate most of these backcountry health risks. Just so you know what needs to be filtered out, here are some facts about diseases that come from drinking bad water:


"Giardia Lamblia" is a protozoan cyst that causes an intestinal infection known as giardiasis. Most people associate the sickness of giardia with severe diarrhea and they are correct in that assessment. Symptoms include diarrhea, abdominal cramps, pale and greasy stools, fatigue, bloating and weight loss. The onset of symptoms is usually immediate but it can take from 5-24 days for them to appear.

Historically, giardia was most commonly found in water flowing below beaver dams, and was given the name "beaver fever." Giardia is now found in most bodies of water. The protozoa multiplies in numbers quickly, allowing the cyst to be easily transferred from one person to another.

Giardia is often unreported because its symptoms are similar to those of many other gastro-intestinal complaints. It is resistant to treatment by iodine and chlorine, and must be trapped by a water filter or killed with the newest chemical alternative, chlorine dioxide.


Cryptosporidiosis is a word that most people can%uFFFDt spell, so it is commonly shortened to crypto. Like giardia, it is caused by a parasite--"cryptosporidium partum." It is much smaller than the protozoa that causes giardia, and is carried by livestock, wild animals, birds and humans.

Symptoms include the same gastro-intestinal maladies as giardia, but can also include headache, vomiting, and fever. It is resistant to iodine and chlorine. So, like Giardia, "crypto" must be filtered out or killed by chlorine dioxide.


Bacteria are microscopic one-celled organisms that most people know by the name of germs. Some are actually used by humans for good but others are causes of diseases. You cannot see bacteria just as you can not see parasites. Bacteria range in size from 0.2 to 10 microns.

Most bacterial infections are not life-threatening but do need to be treated with antibiotics. There are exceptions, however, and one, E. coli, has drawn attention and fear world-wide. E. coli is short for "Escherichia coli," the name of a very large group of bacteria. There are many strains of E. coli but most of them are harmless. Some can cause diarrhea, urinary tract infections, respiratory and other diseases. The E. coli reports that most people hear about refer to E. coli 0157, a kind of E. coli that causes infections by producing the Shiga toxin. E. coli that has its origin in untreated water is usually caused by animal or human feces.


In most countries in North America it is practically impossible to contract a virus from drinking water. That is why for most purposes, a water filter can meet the needs of backpackers. To become ill from a virus you would have to drink water contaminated by virus-borne human feces. This is not highly likely in the backcountry unless a human carrying a virus had personally defecated upstream.

Viruses from water are still common in poor, underdeveloped countries where sanitary conditions can be iffy at best. Other causes can be an untreated sewage plant, septic system, or a poorly placed outhouse. Viruses can only be killed by chlorine, iodine, by boiling water for 30 minutes, or by a water purifier. There are iodine and chlorine-based filters, and a newer design which uses ultra-violet light.

Note that for water filters and purifiers, 0.2 microns is the current EPA standard for removal of cysts, disease bacteria and viruses.

All pages on this topic:
Water Filters | Backpacking Water Filters vs. Water Purifiers | Backpacking Filters/Purifiers Reviews (Top 10) | Bad Backcountry Water: Giardia, Crypto, Bacteria, Viruses
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