A Backpacker’s Guide to Water Filtration

When was the last time you knelt in the soft grass of a pristine alpine meadow and sipped cool, clear water directly from a high mountain stream?

It’s a delightful feeling, but one that’s increasingly rare for cautious hikers who don’t enjoy catastrophic digestive upset. Sipping water from the wrong stream – one with cattle grazing upriver, or too many humans camping nearby – can lead to Giardia, or worse.

Fortunately, water filtration methods are plentiful and cheap these days. They keep getting smaller and lighter too. There’s really no reason not to use one whenever you hit the trail.

But how to choose the best water filtration method? Are they all equally effective? Which ones are most efficient? How do I know if I’m filtering out all the important nasty buggers?

In this guide to water filtration for hiking and backpacking, I’ll answer all these questions and more.

Glacial runoff in Argentina

Special Note for Hiking + Travel

First, an important note for those who like to combine their hiking and travel: you might need a purifier, not a filter, and yes there is a difference.

The filters discussed in this post are appropriate for most backcountry hiking in more developed areas of the world where tap water is considered safe to drink. Developing parts of the world often have additional threats in both tap and natural water that filters alone do not protect against (namely, dangerous viruses).

For more information, see this detailed guide to water purification for international travelers.

Patagonia, Chile

Waterborne Pathogens

First, let’s quickly review our high school biology so we understand the types of nasty little buggers we’re trying to protect ourselves from.

Bacteria

E. Coli, Salmonella, Cholera

Size: 0.2 – 5 microns

Removed by most filters

Killed by chemical treatments

Common in natural water sources in developed countries

Parasites

Giardia, Cryptosporidium

Size: 1 – 15 microns

Removed by filters

Not killed by all chemical treatments

Common in natural water sources in developed countries

Viruses

Hepatitis A, Norovirus, Polio

Size: 0.02 – 0.3 microns

Not removed by most filters

Killed by chemical treatments

Uncommon in natural water sources in developed countries, except places with high human waste contamination

By far the most common problem caused by all of these: diarrhea and other digestive upset. Not usually some mild 24 hour bug… Think weeks of uncontrollable digestive problems.

How does water get contaminated?

As far as I can tell, basically all the waterborne pathogens we worry about come from fecal contamination of water sources. Yup that’s right: poop gets in the water we drink and makes us sick. I know, gross.

How? Poop is a great carrier of all the nasty germies already inside the intestines of people and animals. When an infected person or animal poops and the waste makes its way into a water source, the bacteria, parasites, and viruses in the poop end up in the water. The person or animal doesn’t even need to be actively ill; we can be carriers and spreaders of these pathogens without showing symptoms.

If you follow this to its logical conclusion, you’ll understand that the most highly contaminated water comes from areas that are either downstream from a lot of animal grazing or agricultural land, or areas where human waste isn’t contained by a sewage system (which in the backcountry usually means popular camping areas).

Gorgeous river in rural Patagonia, but look closely and you’ll see a herd of guanaco in the distance. Their poop could contaminate the water.

Filters Versus Purifiers

Yes, there’s a difference. Filters work by physically straining out bad stuff – bacteria and parasites – with tiny pores that they can’t fit through. When using most backcountry water sources in developed countries, a filter is sufficient.

Filters don’t protect against viruses though, because viruses are too small. They slip right through the pores. Only “purifiers” – which use an additional method like chemical or ultraviolet treatment – can deal with viruses.

Viruses are typically only a concern in developing countries where sanitation infrastructure is not yet up to snuff, allowing human waste to contaminate water sources.

However, certain popular recreation sites in the US have been involved in virus outbreaks in the past. If drinking water from a lake with a lot of human activity nearby, you should consider a purifier or combine your filtration with a chemical treatment.

What about Cryptosporidium?

This hard-shelled parasite, (un)affectionately called Crypto for short, is in a class of its own. It’s large enough that filters can easily strain it out, but for those using chemical treatments it presents a challenge. Its hard shell is resistant to chlorine and iodine.

Chlorine dioxide will get it eventually, but requires four hours to work for sure. Chemical treatments are a popular choice with lightweight backpackers, but unless they’re using chlorine dioxide and waiting a full four hours to drink the treated water, they’re taking a risk with Crypto.

So, is Crypto common enough to worry about? *Shrug…* It definitely does exist in the United States, especially in areas with heavy contamination from human or animal waste. The risk is yours to take.

It may be reasonable to drink that chlorine dioxide treated water after 30 minutes (not long enough to kill Crypto) if it’s from a high mountain stream with no animal grazing land and very few campsites upstream. But in a lower elevation area with plenty of potential for upstream contamination, I personally wouldn’t risk it.

This lake in Patagonia looks pristine, but there’s a campground and some cattle pasture nearby.

Do you really need to filter your backcountry water?

It’s your hike, your potentially uncontrollable diarrhea, your choice. The general consensus from the outdoor community is definitely yes, you should filter your water.

I filter or chemically treat nearly all my backcountry water and would recommend you do the same. Filters these days are affordable, lightweight, small, fast, and easy! Gone are the days of slaving over a low-volume pump for what feels like hours while your fingers freeze and your camp dinner gets cold.

If you like living dangerously, you may choose to take a calculated risk and not filter your water in some very specific places. Typically, understanding that water gets contaminated by animal and human excrement, these should be places with almost no chance of humans or animals upstream. Very high elevation streams in very remote places may qualify.

Gorgeous alpine lakes on the John Muir Trail. Though high elevation and remote, they could be contaminated by human waste from hikers on this popular trail.

Types of Water Filters for Backpacking

Fortunately for us hikers, outdoor gear companies continue to innovate in the water filtration space. The result is a confusing abundance of options for every budget and style.

Here are a few of the most popular water filtration methods for hiking. This is subjective, but I’ve ranked them roughly in order of how well suited they are for hiking and backpacking, from most to least.

Gravity Filter

Maybe I’m lazy, but I love gravity filters. Simply fill a reservoir, hang it from a tree or place it uphill, and let gravity push the water through the filter and into the clean bag while you eat your snack or set up camp.

They’re easy, and quite convenient for filtering large amounts of water for filling hydration bladders and for using around camp. They are also getting smaller and lighter by the year, making them excellent choices for lightweight backpackers.

Most filter elements need to be periodically backflushed or cleaned, will eventually need to be replaced, and can be damaged by hard impacts or freezing temperatures. Handle carefully and cuddle up with them in your sleeping bag on cold nights.

Squeeze and Inline Filters

These use similar filter elements to gravity filters, but with a different setup.

Squeeze filters like the Sawyer Mini are sort of like gravity filters, but meant to work faster if you squeeze the dirty reservoir to push the water through the filter. In practice, at least with the Sawyer Mini, they also work as gravity filters or inline filters when set up accordingly.

An inline filter is meant to be attached “inline” with your hydration bladder hose, allowing you to fill the bladder with dirty water. As you drink, the water is pulled through the filter and into your mouth. This is probably the fastest option for filling up and hitting the trail quickly. But it’s less convenient when you need a larger quantity of filtered water around camp (say, for cooking food when you don’t plan to fully boil the water).

Inline and squeeze filter elements, being very similar to gravity filter elements, have the same issues: limited (but long) lifespan, periodic backflushing, damage from dropping or freezing.

Pump Filter

My very first backcountry water filter was a pump filter. They are excellent for getting water from shallow sources where a reservoir is hard to fill, and can be efficient with large quantities of water. They also will keep your upper body in shape along with your legs on a long backpacking trip!

While some very good pump filters exist, I personally prefer the hands-off convenience of a gravity filter. Pumps also tend to be bigger and heavier, making them less suitable for lightweight backpacking.

Chemical Treatment

Chlorine dioxide is the only chemical treatment approved for Crypto, and it takes four hours of treatment time, which is challenging for most hikers to arrange. No one wants to carry around a bunch of extra water that they can’t drink for hours.

Therefore, while chlorine dioxide is appealingly lightweight, it’s a risk to use it in areas with higher human or animal activity upstream. A few tablets can make a good emergency backup to a filter system though.

Chlorine or iodine don’t work at all against Crypto and tend to have a more objectionable taste, making them even less appealing.

UV Purifier

UV purifiers like the SteriPen are technically not filters (they protect against viruses too), but I’m including it for completeness. It’s a small, battery-powered device that purifies a bottle’s worth of water by inserting it, pressing a button, and waiting for a bit.

They are fast and easy, but awkward for cleaning large amounts of water in multi-liter hydration packs. They also have the potential to fail or run out of battery. Most importantly for backcountry applications, they’re not effective in cloudy water; they neither remove the gross particulate matter nor kill pathogens effectively.

Bottle Filter

Despite the large number available on Amazon, I don’t see many serious backpackers using filter bottles. Though convenient for a single bottle’s worth of water, they’re unsuitable for filling a larger hydration bladder for long miles or hot weather. The only case I can see them working well for is a day hike in an area with frequent water sources.

Straw Filter

Like bottle filters, I’m not quite sure what the best use case is for straw filters in the backcountry. They only allow you to drink when actually at a water source, instead of filling a reservoir to take with you; I know basically no one who manages water this way while hiking.

They also seem redundant. A cartridge from a gravity or squeeze filter could be used as a straw filter if needed, while being far more versatile. They might make a reasonable backup, but chlorine dioxide tabs are far cheaper and smaller. If I’m missing something, let me know in the comments below!

Which water filtration method is best?

Excellent question! This will depend on personal preference, where and how you like to hike, and the size of your group. That said, I can make a few recommendations based on my personal experience:

  • Fast and light solo hikers: squeeze filter like Sawyer Mini with option to set up inline; or in low-risk areas, just chlorine dioxide
  • Couples or groups sharing gear, or whenever size and weight are not major concerns: large-capacity gravity filter system like the Platypus 4 liter GravityWorks
  • Emergency backup in all cases: a few chlorine dioxide tablets
One of a zillion gorgeous alpine lakes on the John Muir Trail

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About the Author

Hi there, I’m Alissa. I’ve had the pleasure of hiking the Arizona Trail, Colorado Trail, John Muir Trail, Tahoe Rim Trail, and countless shorter amazing trails throughout the US and abroad. I love solitude, big views, and a good lightweight gear setup. Learn more or say hi.

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Pictures of water filters and water treatment methods, with text: Hiker's Guide to Water Purification in the Backcountry
Picture of stream with text: Guide to safe drinking water in the backcountry
Pictures of water filters and water treatment methods, with text: What's the best water filter for backpacking?

6 thoughts on “A Backpacker’s Guide to Water Filtration”

    • Hi, nice site you have! It always makes me happy to see more ladies getting out there on bikes.

      For bikepacking I mix and match. For longer or more leisurely trips I use my Sawyer mini with a CNOC brand bag (available on Amazon and way easier to use than the Sawyer ones). For shorter or lightweight trips, or trips where I can often refill from safe sources, I bring chlorine dioxide drops. On trips where I might drink often from very contaminated sources (rivers in heavily populated areas, international trips in developing countries) I would use both, because the Sawyer filter isn’t effective against viruses and the chlorine dioxide takes 4 hours to be effective against certain parasites.

      Reply
  1. Great post! Do you recommend using the tablets in addition to the filtering? We use a Sawyer gravity system, but I’m wondering if we should use tablets as well. That Crypto is nasty stuff.

    Reply
    • It depends on where you are and what kind of water you’re drinking. In most of the US and Europe a Sawyer should be fine (including for Crypto). I personally only add chlorine dioxide drops in addition to a filter when I’m traveling abroad in countries without strong sanitation infrastructure. The drops deactivate waterborne viruses, and the Sawyer filters bacteria and parasites, so the combo is a pretty sure bet against most nasty stuff.

      Reply

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