Have We All Been Filtering Our Water Wrong the Whole Time?

On a recent backpacking trip, I stopped at a stream to filter water along with some other hikers. We were making hiker trash small talk (“Man, I’m starving. What’s your trail name? Have I told you about how gross my feet are yet?” etc. etc.) when I noticed one of my fellow hikers’ strange approach to water filtration.

First, he collected stream water in a smart water bottle. He then screwed a filter onto the bottle to purify and transfer its contents into a clean water bladder. Everything checks out so far. But then he poured that clean water back into the very same dirty water bottle. And then drank it!

backcountry water filtration

Photo by Bit Cloud on Unsplash.

My tender, former-chemistry-lab-tech heart quavered. Putting clean water back in a dirty container is far from best practice for water purification. Granted, the human immune system doesn’t care nearly as much about trace levels of contaminants as, say, a mass spectrometer, but still.

Filtering the water may have taken out any microscopic creepy-crawlies that had been living in it. However, contaminants could remain in the several milliliters’ worth of droplets clinging to the sides of the dirty water bottle. By pouring the clean water back into the same bottle without sterilizing it, my new friend had just reintroduced potential pathogens back into his drinking water.

And the ineffectual water filtration practices I’ve witnessed over the years don’t end there.

Bad water filtration practices are everywhere.

I’ve seen hikers meticulously filter all their drinking water, only to later wash their dishes, hands, and/or teeth (!) with unfiltered stream water. Or “eyeball” the amount of chemical purifier they added to their bottle and start drinking right away without letting it react first (it typically takes at least 15-30 minutes for droplets to purify a liter of water).

What’s more, nearly every hiker—including me—has let a few careless dribbles of unfiltered water drip onto the mouth of their water bottle from time to time.

(The risk of getting sick from just a few unfiltered drops is pretty small unless you’re drinking literal sewage—but if, say, you’re filtering from a stream that’s also used heavily by livestock, those droplets start to look more sinister).

“We can be fully confident in {our filters’} operation,” said Travis Avery of Sawyer Products, a company that manufactures a line of water filtration products, pointing out the extensive testing and quality control each filter undergoes before hitting the market. So when someone gets sick even after filtering their water, Avery says poor sanitation habits, cross-contamination with dirty water, or damage to the filter due to freezing are usually the culprits.

Yet all of the above pale in comparison to the small-but-vocal contingent of hikers who proudly abstain from filtering their water altogether. “Drank liters of this unfiltered today,” boasted one Colorado Trail Guthook user in a recent comment on a water source. “If I haven’t updated this comment in 48hrs go for it!”

This sentiment is the backcountry equivalent of “we never wore seatbelts back in my day, and I never got launched through a windshield at high velocity—why bother buckling up?”

You can’t know for sure what’s lurking just upstream.

backcountry water filtration

Photo via Max Kiel.

When you’re drinking water from remote mountain streams, the risk of contracting a waterborne pathogen is small—especially if you’re only dealing with a few unfiltered milliliters diluted in otherwise clean water. But it exists. After all,  a seemingly pristine creek might have a giardia-laden beaver pond or a decomposing moose carcass submerged in its waters a quarter-mile upstream.

And it only takes one (literal) asshole leaving unburied shit just out of sight along the riverbank to create a significant health hazard. This is a thing that actually happens, guys. With surprising frequency. I’ve discovered fresh turds right on the banks of streams that hikers drink from all too many times.

Once, while scouting out campsites near a beautiful creek in Colorado, I stumbled upon a small crowd’s worth of unburied poo and toilet paper right next to the water, about 30 feet upstream of the trail crossing. I was lucky to discover this gruesome scene before collecting water, but most hikers just passing through the area would never guess that there were turds and TP strewn all over the stream bank just above the point where they were collecting drinking water.

So, yeah. Rogue backcountry poopers are killing my faith in humanity (and, by extension, safe drinking water sources).

All it takes is a little crappy luck and carelessness.

Humans can contract giardiasis, a relatively common waterborne disease caused by the protozoan Giardia duodenalis, by ingesting as few as ten cysts. Another North American waterborne pathogen, cryptosporidium, can infect with even fewer cells.

Both illnesses typically involve extreme stomach cramps, projectile vomiting, explosive diarrhea—the whole nine yards. To make matters worse, infections can sometimes last weeks.

All it takes is a little bit of carelessness and crappy luck—no pun intended—and you only have to get sick once to seriously regret every life choice that led you to that point.

Waterborne illnesses aren’t as common as they once were thanks to improvements in safe drinking water standards and environmental protections. But they’re still a thing. “Pre-COVID, about 50% of all global hospitalizations were waterborne disease-related,” points out Avery of Sawyer Products. That’s factoring in all global communities, including some that have extremely limited access to clean drinking water.

But even in the US, a recent CDC study identified over seven million illnesses attributable to waterborne pathogens in 2014 alone, resulting in hundreds of thousands of hospitalizations. Giardiasis and cryptosporidiosis were the third and fourth most common drivers of waterborne disease in the study.

Waterborne diseases are not fun.

A scanning electron micrograph of the surface of the small intestine infected with Giardia sp. protozoa. Image from Public Health Image Library (PHIL).

If you are one of those unlucky folks who contract a severe case of a waterborne disease like giardiasis, the price is steep. You’ll potentially end up spewing out both ends for miserable days or weeks on end. You’ll likely become dehydrated and won’t be able to hold onto calories either.

If that happens to you while you’re in a remote backcountry location, well, that’s terrible news. (It’s always a good idea to carry over-the-counter anti-diarrheal pills to stave off severe dehydration until you can get help, by the way).

And here’s the kicker: you won’t necessarily become symptomatic right away. Symptoms of giardiasis don’t emerge for six to 12 days after the initial infection, and other pathogens have similarly long incubation periods.

While the odds of getting sick may be fairly low, the stakes are high. Giardiasis sucks, or so I’m told.

Is it worth the risk?

Filtering is so easy! Why wouldn’t you just do it?

backcountry water filtration

A simple, gravity-fed water filtration setup using a CNOC collection bag, Sawyer Squeeze, and clean water bladder. Photo by Harvey Howard.

The Sawyer Squeeze, by far the most popular water filtration method among thru-hikers, costs just $36 and weighs in at a measly three ounces. You can buy one at most outfitters and even Walmart. If it’s properly maintained, a regular-size Sawyer can filter a liter of water in well under a minute. Sawyers last a long time and are easy to use and take care of.

“I’m proud that some of our Squeeze filters are approaching 13 years” of continuous daily use, says Avery—though he stresses that proper maintenance and cleaning practices are essential to maximizing the filters’ longevity.

There are many, many options for filtering and/or purifying your water, from fancy UV devices like the Steripen, to hollow fiber filters like the Sawyer or the Katadyn BeFree, to repurposed eyedrop bottles full of bleach.

There’s a water purification solution out there for every budget and every base weight.  With so many readily available options,  I have to wonder: why wouldn’t you filter your water? The additional effort is trivial.

Don’t forget about microplastics.

Backcountry water filters like the Sawyer Squeeze can remove microplastics from drinking water. Photo via Camacho.

We now know that microplastic contamination of the world’s surface waters is widespread—even seemingly pristine headwaters aren’t immune, as microplastics can literally rain down from the sky in remote mountains.

The ecological and health implications of ingesting microscopic plastic particles still aren’t well understood, but one wonders—and scientists are actively investigating—whether doing so might be less than ideal for your health.

Granted, microplastics are everywhere and we ingest them every day regardless of where we’re getting our water from. They’re in the food chain, they’re in urban water supplies, and everything from plastic food and drink containers to synthetic clothing produces more microplastic contamination every day.

But 0.1-micron filters like the Sawyer Squeeze are fine enough to remove microplastics, which means the drinking water you filter in the backcountry should be safer to ingest than the stuff that comes out of your tap back home.

Is backcountry water filtration the silver bullet that will save you from the as-yet-unknown effects of ingesting microplastics? Probably not, but it’s a step in the right direction and a compelling additional reason to filter your water.

Safe drinking water requires more than a good filter.

Once upon a time, a friend of a friend on the AT switched from a Sawyer Squeeze to Aqua Mira drops near the end of his hike but didn’t let the drops react with the water for the appropriate amount of time.

So even after using the drops, he ended up getting some waterborne bug while deep in Maine’s Hundred Mile Wilderness. Long story short, he shit himself, slathered his arms and legs in alcohol-based hand sanitizer to clean up, tried to use the flame of his Bic lighter to inspect the damage (it was late at night and he couldn’t find his headlamp), and subsequently lit himself on fire because of the alcohol fumes. He’s fine now by the way.

Moral of the story: beyond the filter/purifier itself, a little care goes a long way toward keeping your drinking water clean. Don’t let operator error be the reason you get sick.

Follow these guidelines for safe water filtration.

  • Use a dedicated container for collecting “dirty” water from streams. Never store clean water in the dirty water container or drink directly from it. No mixing!
  • After filtering, pour some clean water over the mouth of your bottle or wipe it off with a bit of cloth to remove any stubborn contaminated droplets.
  • Dry your hands after handling stream water and before eating or drinking.
  • If you’re using a hollow fiber filter like the Sawyer, don’t let it freeze. Any water in the filter will expand as it freezes, potentially damaging the pore structure so that contaminants can pass through. There’s no easy way to tell if your filter has been damaged, so proactively keeping your filter in a warm place (ie the inside of your sleeping bag) in cold weather is key.
  • Backflush thoroughly and often! Your filter won’t clog up that way and will be easier and faster to use. Try tapping the filter against the edge of the sink to help dislodge stubborn sediment as you backflush.
  • If using chemical purification methods, read the instructions first. Make sure you use the right amount and that you let it sit for the appropriate interval before drinking. Most methods take hours to kill cryptosporidium.
  • Take steps to protect other hikers and aquatic life too: make sure you’re 200 feet away from any water source before digging a cathole or washing your hands or dishes (never wash directly in the water!).

Proactively choose low-risk water sources.

backcountry water filtration

Marginal water sources like this disgusting cow tank are very common on arid trails like the PCT and Arizona Trail. Yikes. Photo via Katie Gerber.

All this is great. But the most proactive thing you can do to limit your risk is to choose your water sources carefully. Follow these guidelines:

  • Flowing water is better than stagnant—moving water affords less chance for things to start growing. For instance, instead of collecting water directly from a lake or pond, try gathering from the inflow.
  • Springs are better than streams—spring water comes straight from underground and has spent less time bumming around on the surface than stream water. The closer to the source of the spring you can collect, the better.
  • Avoid beaver ponds and their outflows like the plague (“beaver fever” is another name for giardiasis).
  • Very important: stay away from water sources in known agricultural watersheds and near highways and towns/cities. Heavy metals, pesticides, car exhaust, and other forms of pollution are not your friends. And most water filters won’t do a thing to mitigate them.
  • The smaller the stream, the less likely it will be contaminated because it’s likely draining a smaller area.
  • If the water source is flowing across the trail, collect from the upstream side. The further upstream you can reasonably collect from, the better.
  • Sometimes you can’t avoid marginal water sources. For instance, on arid trails, hikers often must share water sources with free-range livestock. If the water seems questionable, use a secondary purification method, such as Aqua Mira droplets, in addition to your filter. That way, any crawlies the filter misses will get a hit of chemical purification too.

Also, remember to wash your hands.

When customers report getting sick from their drinking water even after using a filter, “up to 30% of illnesses in that area are attributed to washing and sanitation,” says Avery.

In other words, if you’re not washing your hands frequently when you’re hiking, you yourself could be getting germs in your lovingly filtered water or ingesting them directly when you eat with your hands.

A few years ago a controversial article on Slate claimed that filtering backcountry water is medically unnecessary, citing research in which the majority of hikers sampled had been sickened by their own dirty hands, not by contaminated water.

Whether the scope of this research is sufficient, on its own, to make a blanket claim that filtering your water is wholly unnecessary is questionable at best. But the fact remains that washing your hands after going to the bathroom is really easy and will certainly reduce your risk of contracting and spreading illnesses.

Personal hygiene and contaminated water are both risk factors in the backcountry (and they’re not unrelated either), but you don’t have to pick and choose how you approach these risks. There’s no reason you can’t wash your hands and filter your water.

So, to sum up…

Are you overwhelmingly likely to get sick if you accidentally ingest a small amount of unfiltered water? No, but stuff happens. Events outside your control can stack the odds against you. What you can control is whether and how well you filter or purify your water. And fortunately, it’s pretty easy to do.

Also, consider this: our trails are more crowded than ever since the pandemic struck. While we’re happy to see more people getting outdoors, many once-pristine areas have taken a noticeable downturn in sanitation.

“I don’t expect any first-time backpacker to be fully aware of the seven principles or the Leave No Trace mentality,” admits Avery. But most people out there, including first-timers, “have a general appreciation for the outdoors, so they’re almost always open to learning more.”

These days, there are plenty of beginner outdoorspeople out there who just plain haven’t learned how to protect our water sources. Help them along if you have the opportunity and they’re open to it. And in the meantime,  be proactive in protecting your own health and safety.

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Comments 13

  • pearwood : Sep 7th

    Well said. Thank you.

  • Jerry Floro : Sep 8th

    Great article, Ibex — LOL for the poor person who set themself alight. But with regard to microplastics — so, we filter to remove them, and then keep our water in a plastic bottle, right?

    OK, I get it — microplastics are probably accumulating and concentrating in the natural water supply over time, vs. being in a bottle for a few hours.

    • Kelly Floro : Sep 8th

      Dad, yep I would assume drinking from a plastic water bottle is also a problem, especially the old, beat-up SmartWater bottles most hikers use… some hikers just keep their filters attached to the top of their water bottles at all times and filter right into their mouths. That’s probably the best solution for hikers for whom microplastic contamination is a major concern.

  • Turtle Man : Sep 9th

    Great article!

    Given the increasing number of, uh, under-educated (i’m being charitable) trail users, this information needs to be re-iterated as often as possible. I’ve watched YouTube vloggers soaping up at the side of a pond on the Long Trail. I’ve seen, firsthand, people throwing food debris into the woods at shelters. Encountered toilet paper blowing around along the side of the trail. Had to step over thru hikers camped, literally, on the trail coming off of Franconia Ridge. The increasing level of disrespect or ignorance seems to result from some sense of entitlement and disregard for other backcountry users and the environment.

    Couple of things not mentioned re. water filtering: Pre-filtering water that contains a lot of silt or other suspended stuff through a piece of cloth or a coffee filter will keep your filter going longer before it starts to clog up. And when back flushing, it takes a significant amount of pressure to force out the particles that get lodged in the filter matrix. That’s why Sawyer supplies a syringe—which many people leave behind to “save weight.” Simply running water through at gravity pressure is unlikely to adequately clean the filter.

    In related news from the Department of Irresponsibility, here’s another story for you: An Eastern Continental Trail hiker, recently in Maine, reports that his support person learned that a hostel had some of their staff contract Covid, but, apparently, they haven’t notified hikers, or the ATC. I can find no information about that—nor any Covid protocol’s at all— on the hostel’s website, and no report of the outbreak on the ATC website. You can check out the YouTube video of First Church of The Masochist Hikes, episode 91 where he discusses this situation.

  • Darrell Lee Chapman : Sep 10th

    What do you think about the Life Straw?? Any thoughts on how well this works with filtering water while out hiking or camping?

  • Steven Allen Boothe : Sep 10th

    I mostly day hike 10+ miles and definitely filter water and learned mostly from YouTube videos etc…… Anyways, I watched someone do exactly that. I was like what are you doing? Dirty bottle = dirty water ALWAYS. His answer, I haven’t gotten sick yet. His thinking his way is good will catch up to him one day.

  • david putnam : Sep 11th

    Painfully hilarious watching and listening to the ill prepared,underskilled,lost in the great abis outside their bedrooms milenials wandering through endless misteries of what the hell to do in the outdoors. So hey kids, we “old schoolers” did the whole dang kit n kabootle whithout a phone….just a usgs map and sometimes a compass. And,here in the sierra,before giardia arrived no thanks to the xattle ranches free ranging in these mountains. And….we carried out all our garbagiola.

  • Elder Woodsman : Sep 12th

    The USFS and BLM provide grazing permits on millions of acres in Colorado. That includes the headwaters for the majority of Colorado’s streams. Forty years ago I packed in and set up what I thought was the perfect archery elk camp. The next day I headed up to the beautiful timberline basin I expected to hunt only to discover it was now occupied with sheep. I had drank plenty of the contaminated water and over the next couple of weeks I paid dearly for the experience. The treatment for severe giardiasisis is nearly as bad as the infection. I will all ways carefully select and treat my water.

  • larry contrary : Sep 14th

    Just a note: “Marginal water sources like this disgusting cow tank are very common on arid trails like the PCT” This statement is not true. I have thru hiked the PCT five times and have never seen, nor have had to collect from, any marginal water sources.

  • Matt H. : Sep 17th

    Great article. Also wanted to add that alcohol based hand sanitizers do NOT kill cryptosporidium or noro virus.


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