Should You Treat Water in the Backcountry? What Science Says.

The internet is a vast source of information, good and bad. It’s easy to find information “proving” just about anything.

I have been studying this topic for several years. This CDC statement sums things up well: “Although the advice to universally filter and disinfect backcountry drinking water to prevent disease has been debated, the health consequences of ignoring that standard water treatment advice have been documented…

“How common are backcountry pathogens?”

The EPA’s Giardia: Drinking Water Health Advisory says, ” Cysts have been found all months of the year in surface waters from the Arctic to the tropics in even the most pristine of surface waters… In three pristine watersheds in Washington, Ongerth Giardia cysts in 43% of 222 samples… Hancock in 14% of the springs…Roach… found Giardia cysts in 32% of samples collected from pristine streams…Hibler (1988) found Giardia cysts in 19% of springs…”

“How about Appalachian water?”

Backpacker Magazine did a survey and said: “…In our study, the two sites along the Appalachian corridor collectively tested positive for giardia cysts 50 percent of the time…”

The paper Bacterial water quality: springs and streams in the Great Smoky Mountains National Park said: “Levels of fecal coliform and total coliform in most water samples were unsuitable for drinking without treatment. As a result of these findings, park managers increased efforts to inform visitors of the need to treat drinking water and removed improvements at backcountry springs which tended to give the springs the image of safe, maintained water sources.”

“I read that there aren’t enough giardia cysts in backcountry water to make you sick.”

Not true. The definitive paper Risk assessment and control of waterborne giardiasis has shown that there is a ~2% risk of infection with a single cyst.

“I know people who have gone for years drinking untreated water without getting sick!”

I think hand washing is one of the best analogies. Germs are ubiquitous on hands, yet rarely can we verify that dirty hands have made us sick. Still, we know routine hand washing helps keep us healthy, regardless of our past experience.

“But people aren’t actually getting lab-tested. And giardia is rare in any case.”

An outbreak of giardiasis in a group of campers found 25 other campers had stools examined before and after a subsequent hiking trip in another area of Utah; none had Giardia cysts before, but 6 (24%) had them after return.

Cyst acquisition rate for Giardia lamblia in backcountry travelers to Desolation Wilderness This study’s lab tests found 5-8% of tested hikers picked up giardia on a single trip.

Drs. Thomas and Timothy Welch are among the greatest sources of misinformation on giardiasis and water treatment. They called backpacker giardiasis “extraordinarily rare.” Obviously untrue. I debunk their research here.

“But I heard there is more giardia in tap water than backcountry water!”

That erroneous idea comes from an article by Robert Rockwell. Yes, there were cysts found in tap water, but 99.99% were dead, killed by a modern treatment plant. City water is much, much safer than untreated backcountry water. I have debunked Rockwell’s writing here. Most claims that sickness from backcountry water is a “myth” trace back to Drs. Welch and Rockwell.

“Still, we know the main issue for backpackers is hygiene.”

There is no DATA to support that theory. I have only found one paper that compared water treatment and hygiene, Medical risks of wilderness hiking. This was a prospective surveillance study of 334 persons who hiked the Appalachian Trail. They found water treatment was more important…

The risk of diarrhea was greater among those who frequently drank untreated water from streams or ponds (odds ratio = 7.7; 95% confidence interval : 2.7 to 23; P <0.0001), whereas practicing “good hygiene” (defined as routine cleaning of cooking utensils and cleaning hands after bowel movements) was associated with a decreased risk (OR = 0.46; 95% CI: 0.22 to 0.97; P =0.04).”

“But hiker hands are filthy!”

High fecal hand contamination among wilderness hikers found, “The prevalence of fecal hand contamination in entering and exiting hikers was similar (33% and 27%, respectively)”. Hiker’s hands were CLEANER at the end of the trip than when they started. The largest study of non-hikers hands that I could find, Isolation of bacteria of faecal origin on commuter’s hands: a preliminary study, involving British commuters, found (28%) had fecal bacteria present, HIGHER than hikers leaving the field.

“But do we KNOW hikers are getting giardiasis from backcountry WATER?”

Yes. Giardiasis in Colorado: an epidemiologic study, looked at 256 lab-verified cases:

“…an increased incidence of giardiasis camped out overnight (38% vs. 18%), and drank untreated mountain water (50% vs. 17%), p less than .001. Also identified was a correlation between the seasonal distribution of cases and degree of fecal contamination of mountain streams….drinking untreated mountain water is an important cause of endemic infection.”

Additionally there have been CDC verified waterborne giardiasis outbreaks among campers and backpackers. And, according to the CDC, over 99% of giardiasis cases are endemic (regularly occurring) and not part of outbreaks.

“What about other pathogens?”

The paper Cryptosporidiosis and surface water found: There was a strong association between drinking surface water and illness.

A paper called Campylobacter enteritis from untreated water in the Rocky Mountains concluded: “These studies show that backcountry surface water can be an important source of C. jejuni and that infection with Campylobacter, as well as Giardia lamblia, should be considered as a cause of diarrhea in those who have recently returned from wilderness areas.”

Usually we can get by with drinking untreated backcountry water, but there is no doubt that consistently treating or filtering of drinking water, along with hand and dish washing, will significantly reduce the odds of an extremely unpleasant or hike-ending illness.

Buck “Colter” Nelson is a three time veteran of giardiasis. He as completed the Triple Crown and was the first to thru-hike the Desert Trail. He documented a solo traverse of Alaska in his film Alone Across Alaska and survived 70 days living exclusively on wilderness foods, a story told in his new book Alone in the Fortress of the Bears. Both are available at

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Comments 13

  • Christian : Jan 4th

    Good read! Thank you for the information, Colter!

    • Colter : Jan 10th

      Thank you Christian!

  • TBR : Jan 5th

    Excellent post — hikers everywhere are grateful, especially those who might have been in doubt.

    How about a followup on your recommended means of treating water?

    • Colter : Jan 10th

      Thank you TBR.

      Not a full followup but I’ve used several different types of water treatment. My favorite for long trips is Aquamira drops. I think the Sawyer Squeeze is also a good choice. I like simple.

  • Hoot Al : Dec 17th

    Ever since I observed a doe going to the bathroom in the middle of a stream, I always filter my water.

  • Carl : Dec 19th

    Wow, crazy irresponsible conclusion. You wrote all that and then just encouraged readers to “get by”.

    Truth is, if you filter you won’t get sick; period. No chance, not gonna happen. Only sensible recommendation. ALWAYS filter.

    Every person I know who became sick from not filtering, they ALL filter NOW. Well, except for the author…who sounds as if he’s working toward illness award number 4.

    • Colter : Dec 20th

      I think you’re the first person to draw the conclusion that I’m encouraging people not to treat/filter Carl!

  • Tortuga : Jan 15th

    Excellent article using great credible references. I bought Sawyer squeeze for my 2017 NOBO A.T., and will also pick up some Aquatica drops. Thank you.

    • Colter : Nov 17th

      Thanks Tortuga! I hope you had a great hike.


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