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Water Safety and Treatment in the Outdoors

Updated: Sep 23, 2023

When, where, and how to treat water in light of new data

Photo by PeopleImages on IStock


Reasons to filter your drinking water have increased over recent years. No longer are Giardia, farm runoff, or even heavy metals the biggest health concern while tramping. New data show the global water cycle is contaminated with carcinogens, with even the most remote areas of the planet (Antarctica) having rainwater that’s contaminated beyond every safety standard. We urge everyone to filter drinking water both when hiking and at home. In addition, the popular size exclusion methods are no longer sufficient. Luckily, granulated charcoal does appear to remove most of the contaminants.

To treat your water or not.

You will find many opinions on the topic, from where is safe or not, what methods or tools to use, and debates about how well filters even work in the first place.

This article is written as a definitive answer to all these questions using the most up-to-date science on the subject. Few topics in hiking can be written about with such conclusiveness, but the jury is no longer out and it’s mostly bad news.

The truth is, you’re probably doing it wrong; especially ultralighters like ourselves. The good news is that there is a solution, and it’s not that much heavier than the most popular options.

Why you should treat your water and why your “iron stomach” isn’t cutting it.

Giardia seems to get all the attention, and this stomach bug can certainly ruin a trip but it isn’t everywhere yet. As your favorite remote trail gets more attention, you should begin to get more worried about this.

Other common concerns are heavy metals (mostly from road run-off) and contamination from farm run-off. You can also avoid these issues by being smart about where you gather your water.

However, what I suggest you be more worried about is something that can’t be avoided; and, unlike giardia, it doesn’t leave your system and only gets worse with time.

That problem is a class of chemicals called PFAS (per- and polyfluoroalkyl substances) which don’t break down, hence their common name “forever chemicals”, and are increasingly being linked to various cancers and other life-long and multigenerational health risks. You will be familiar with these chemicals from non-stick pans, Gortex, and basically any “water-resistant” material.

But it turns out these chemicals have polluted the water cycle itself above safe levels- meaning the rainwater that’s used in huts contain these chemicals. A recent study has shown dangerous levels of PFAS in rainwater all over the planet, including Antarctica.

“Although PFAS are globally present in all environmental media and locations, there are still some few areas of the planet where the environmental levels of PFAS remain relatively low. However, even in these remote and sparsely populated regions, such as Antarctica and the Tibetan plateau, the most stringent PFAS guidelines are exceeded” - Cousins et al., 2022 (1)

If you would like to read a news report on the findings, which may be more digestible, you can follow the link at the end of this quote discussing reasons PFAS should be avoided:

“A host of possible serious health consequences has been associated with PFAS, including cancer, infertility and pregnancy complications, immune system problems and increased cholesterol, according to researchers at Stockholm University and ETH Zurich.” - USA Today, Link

These PFAS are not destroyed by boiling water, they build up in the body over your lifetime, and can be passed to your children. If you’re looking for a reason cancer is increasingly common, this is a pretty strong candidate.

The American Cancer Society has a nice set of links to other data, and concludes with:

"According to the US Centers for Disease Control and Prevention (CDC), people whose regular source of drinking water is found to have higher than normal levels of PFOA or similar chemicals might consider using bottled water or installing activated carbon water filters." American Cancer Society, Link

We now know that all outdoor water sources should be considered to have "higher than normal levels" of these chemicals, so this advice likely applies to you!

Likewise, there is a growing concern over microplastic accumulation in our bodies (though with notably fewer links to negative outcomes currently). As with PFAS, microplastics have been found in rainwater. This article discusses related findings from New Zealand, demonstrating high levels of microplastics detected in the rainwater around Auckland (2).

Overall, we should consider that our freshwater sources are likely to be contaminated even in the most remote rivers and huts, with increasing cause for concern the closer we are to large cities.

Water treatment methods.

Not all water treatment methods work for the same range of issues, despite commonly being discussed as interchangeable. The three main categories of treatment are heat, size exclusion, and chemical.

  1. Heat: Boiling water is most often recommended, both in DOC huts and after environmental disasters. Boiling will kill most bacteria, and may destroy some toxins, but does not remove PFAS, microplastics, or particulates. This is useful in a pinch, but doesn’t result in the best tasting water (it’s flat and still has sediment) and doesn’t truly purify the water.

  2. Size Exclusion: this is the most common method used by the ultralight community. The most popular methods are the Katydin BeFree and the Sawyer Squeeze (both having 0.1 micron filters), and the Platypus Quick Draw (0.2 micron filter). These all use the same hollow fibre technology to remove nearly all bacteria, protozoa, microplastics (though not nanoplastics), and even many viruses (but far from all). Notably, they don’t remove heavy metals, small molecules such as chemical contaminants and PFAS, or fine sediments such as sand.

  3. Chemical: This includes sterilization methods such as bleach and Aquatabs, but we can also add UV pens because they have a similar effect. These methods destroy bacteria and protozoa as well as viruses. However, as with boiling, these methods often leave water with poor taste and will fail to remove heavy metals, PFAS, microplastics, and particulates.

There’s also a special case that stands out, both because it’s by far the best option and because it combines two of the above methods. Granulated charcoal acts as both a chemical filter (binding and removing various chemicals, PFAS, heavy metals, etc.) and size exclusion method which helps remove microplastics and other water impurities (3). It does not, on its own, remove bacteria or viruses unless very tightly packed.

Charcoal is at its best when combined with a method to kill or remove the common microorganisms that will make you sick. However, most filters combining these methods are too heavy to be within the scope of ultralight hiking.

So what are we to do?

How we are treating our water going forward.

We want our water as safe as possible. We also like enjoying our water without grit or bad flavors - you probably drink more if the water isn’t gross!

So with that in mind, and weight always of secondary importance to safety, we have created the lightest system that combines a charcoal filter with a proper size exclusion hollow fiber filter. To do this, we combined the 6L Katadyn BeFree gravity filter with a Platypus granulated charcoal filter fitted in line with silicone connection tubes. Together, this weighs approximately 270g - certainly heavier than we wanted, but gives us more confidence than other lighter options while being about half the weight of pumps like the Katadyn Vario.

The BeFree will filter the microorganisms and much of the particulate before the charcoal filter removes the PFAS, heavy metals, and other chemical contaminates. Filtering in this order should also extend the lifespan of the charcoal filter which, unlike the hollow fiber filter, cannot be cleaned and reused.

You can find several other combinations to make this work; but if you want to remove every potential hazard from your water possible while on trail, this is the sort of approach we recommend. I imagine this setup could be adapted from the gravity system to a squeeze system or even hydration bladder if you were being creative!

Final thoughts.

Kiwi Ultralight doesn’t have any profit motive in telling you this, we are just passionate about clean water and healthy environments. This area is only getting worse, and rapidly. What may have worked even a decade or two ago isn’t going to cut it anymore, and the ultralight community is probably one of the hardest to convince simply because doing it right means carrying more weight.

The method we settled on is a bit of a Frankenstein approach to reach the lowest weight with the best filtering effect. We are long-time ultralight hikers, but we are also parents who want the best for our family and for yours. This is one of those things where you just do the best you can. No one is going to remove 100% of the risk from their food and water. Hopefully, this article helps improve your health and safety in the outdoors.

Watch this space, more and more will be talking about it and the companies who make water purification products will have to keep up.


  1. Outside the Safe Operating Space of a New Planetary Boundary for Per- and Polyfluoroalkyl Substances (PFAS). Ian T. Cousins, Jana H. Johansson, Matthew E. Salter, Bo Sha, and Martin Scheringer. Environmental Science & Technology 2022 56 (16), 11172-11179 DOI: 10.1021/acs.est.2c02765

  2. Evidence and Mass Quantification of Atmospheric Microplastics in a Coastal New Zealand City. Wenxia Fan, Jennifer A. Salmond, Kim N. Dirks, Patricia Cabedo Sanz, Gordon M. Miskelly, and Joel D. Rindelaub. Environmental Science & Technology 2022 56 (24), 17556-17568 DOI: 10.1021/acs.est.2c05850

  3. Modeling PFAS Removal Using Granular Activated Carbon for Full-Scale System Design. Burkhardt JB, Burns N, Mobley D, Pressman JG, Magnuson ML, Speth TF. J Environ Eng (New York). 2022;148(3):1-11. doi: 10.1061/(asce)ee.1943-7870.0001964. PMID: 35221463; PMCID: PMC8864563.

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