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So you're hiking in the mountains of some far off land and you stumble across a babbling brook of crystal clear water. You’re thirsty so you cup your hands together and dip them beneath the cool, rippling surface then raising the water to your lips you finally taste the refreshing life giver that is mountain water.

There are three main groups of waterborne nastiness that are most commonly linked to water-related illnesses:

Protozoan Cysts

Protozoan cysts: Cryptosporidium parvum, Giardia lamblia. These things are tiny, like 1 to 300 microns; 1 micron = one-millionth of a meter.

When symptoms first appear: From 2 days to a few weeks. Even ONE protozoa is capable of causing infection.

Critter characteristics: Cryptosporidium and Giardia can both survive weeks, even months, in cold water. Cryptosporidium, not so affectionately nicknamed “Crypto” is an oocyst.  It has a thick-walled shell that serves as a protective barrier for the individual protozoa and makes it more resistant to disinfectants such as iodine and chlorine.

Impact on humans: Terrible, frequent, watery diarrhea. Intense vomiting, gas and intestinal discomfort. Most infections last 1 to 6 weeks with rare chronic cases lasting up to a year. People with weakened immune systems: children, elderly, pregnant women and those with immune system deficiencies need to be extra cautious against contracting crypto.


Bacteria: Salmonella, Escherichia coli (or E. coli),  Campylobacter jejuni, Yersinia entercolitica, Leptospira interrogans and many others. These are even smaller than Protozoa, only 0.1 to 10 microns.

When symptoms first appear: From a few days to a few weeks. The number needed to cause infection can vary widely based on the type of bacteria.

Common impact: Potentially prolonged intestinal discomfort, certainly diarrhea. Though cholera (another potentially serious bacteria) is rarely found in the United States, it is fairly common in some countries and can result in death if not quickly treated.


Viruses*: Rotavirus, enterovirus, norovirus, Hepatitis A, Norwalk virus. Exceptionally tiny, not even a micron thick: 0.005 to 0.1 micron.

*Viruses are rarely found in North American wilderness waters and only purifiers - not filters - eliminate viruses. Be sure to investigate the pathogen risks of your next international destination to ensure you pack the best treatment solution.

When symptoms first appear: From 1 day to several weeks.

Common impact: Diarrhea, intestinal discomfort. An assortment of other potential ailments.


May 9, 2022

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We are More Than an Outdoor Company. Water Filtration, Insect Repellent, Sunscreen & First Aid, from the Backcountry to the Backyard.


My only complaint is that eventually, backflushing won’t be enough. These can clog up after some time and no amount of back flushing will fix its low flow. I went through 2 on the AT. However, it will attach to Smart Water Bottles and most bladders!

Anna Hamrick


Built for backcountry reliability and portability, the Sawyer Squeeze filter is our pick for the best portable water purifier.

Pete Ortiz


The Sawyer Squeeze was (by far) the most common Pacific Crest Trail water filter this year – for the fifth year in a row. It’s a $39, 3 oz / 85 g hollow fiber filter that rids your drinking water of protozoa and bacteria (and floaties). It can be used with Sawyer bags (included with the filter) or with compatible water bottles (Smartwater is the bottle of choice for many hikers).

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