Check out iRunFar’s picks for the best water purification devices for trail runners and ultrarunners.

I’ll never forget the time I ran out of water on a 20-plus-mile run in the mountains. It was August, and I’d gotten an early start, but I was new to long-distance trail running, and I was exploring a new route I’d mapped out a few days prior. As sometimes happens, the trail under my feet did not correspond to the line on the map, and I ran farther and longer than I planned.

Along the way, I shook the last few drops of water from my reservoir. The day grew hot, and my throat became parched and dusty. Fortunately, I got back to the trailhead and the extra water bottle that was waiting in my car before things got serious, but I learned an important lesson and started carrying a water filter after that.

At first, I carried the same gigantic pump filter that I used for backpacking. It took up most of the zippered pocket on the back of my hydration vest, but it was better than getting dehydrated or some sort of infection from drinking untreated water. Over the years, I discovered better options — lightweight, fast-working, versatile filters I could drink from, ultraviolet lamps I could stir in my water, and chemical tablets that would work in a pinch. And now, it seems that the options just keep getting better.

For trail runners, there are numerous water purification methods that can suit a variety of needs and hydration preferences. Some work better for bladders than handheld bottles or small soft flasks. Some options are best for individual use, while others are ideal for a small group that’s refilling together.

Certain methods work best for clear-flowing mountain streams that we runners constantly seek, while other systems, or combinations of them, can purify the most unappealing water sources.

To help you choose the best system for your needs, we researched the world of water purification and tested the best options for trail running. For more background information about water purification for trail running, see our glossary, buying advice, testing methodology, and frequently asked questions.

Use these links to skip quickly to specific products:

iRunFar’s Meghan Hicks uses the Katadyn BeFree 0.6L to filter water from a stream in Colorado. We awarded this the best overall filter for trail runners. Photo: iRunFar/Eszter Horanyi

There’s a good reason the Katadyn BeFree 0.6L is wildly popular among trail runners. It’s small, lightweight, compact, and reliable. The filter and soft flask together weigh just 59 grams and measure about 4.3 inches in length, including the lid. The soft flask of this filter can easily fit in the palm of your hand — and in the pocket of a hydration vest.

In addition to being small and packable, it is simple and easy to use. To operate, unscrew and remove the lid, which contains the filter, and fill the soft flask with water. Clear running water is generally the best option if available. Then, screw the lid back on and drink through the water bottle mouthpiece! If you want to refill additional water containers, turn it upside down and the water will flow on its own, or you can squeeze the soft flask to help push the water through the filter more quickly.

It only takes a minute to filter two liters, though this flow rate will slow over time as the filter becomes clogged. The filter is easy to clean in the field if it becomes clogged — no backwashing or extra tools needed; just swish or shake the bottle with clean water.

To learn more, check out our in-depth Katadyn BeFree 0.6L review.

Effective at Removing: Bacteria, cysts, and sediment with its filter pore size of 0.1 micrometers (0.0001mm)

With a similar design and operation to our other top choices, the LifeStraw Peak Series Collapsible Squeeze 650 ml Bottle with Filter receives the runner-up award when it comes to water purification for trail runners. At 102 grams, it’s noticeably heavier than the Katadyn BeFree 0.6L reviewed above and Salomon Soft Flask XA Filter discussed below, and it’s slightly bulkier, too. The filter and lid together are 5.1 inches in length, so it will still fit easily into a hydration vest, but it’s not the most compact option available. That said, the filter can be unscrewed and removed from the lid, making the whole system more packable.

The bottle material feels thicker than comparable soft flasks, which indicates that it’s durable — yet it still packs down to about the size of a fist. In addition, the filter is housed in a plastic case, which adds weight but increases the protection of the filter’s delicate fibers.

Because the 650-milliliter soft flask is a dark color, it’s tricky to see how much water is in the bottle unless you hold it up to the light. If you’re drinking straight from the bottle, it may not be obvious when you’re running low on water. However, because of the bottle’s size and shape, trail runners will be more likely to use this filter and bottle to refill other water bottles. In this case, its high flow rate and ease of use make it a great choice.

Effective at Removing: Bacteria, parasites, microplastics, silt, sand, and cloudiness with a filter pore size of 0.2 micrometers (0.0002mm)

Although it has some limitations, the Salomon Soft Flask XA Filter is an excellent water filter for trail runners. At 52 grams, it’s slightly lighter than the Katadyn BeFree 0.6L, though its soft flask holds only 490 milliliters rather than 600 milliliters. Its long cylindrical shape is specifically designed to fit Salomon vests and will fit into the front pocket of most hydration vests. The hollow fiber filter is about 4.5 inches long, and — fun fact — since both this filter and the Katadyn BeFree 0.6L filter are designed to fit a HydraPak soft flask’s threads, either filter will work with most HydraPak soft flasks, excluding those with a narrow mouth opening.

The filter also features a hard plastic loop that makes it easier to hold while filling and reattaching the lid. To operate the filter, simply fill the soft flask with water and either drink from the mouthpiece on the lid or squeeze the mouthpiece with your fingers and filter the water into another container. The filter has a high flow rate, which makes the whole process quick.

The only real downside of this filter is that there is no cover for the nozzle to protect it from the accidental splashing of contaminated water, like most of the other filters in this guide. Additionally, you must place your potentially dirty fingers on the mouthpiece if you want to refill additional water bottles. This adds a risk of contamination unless you disinfect your hands first.

Effective at Removing: Bacteria and protozoa

While we generally didn’t consider pump filters in our “best for trail running” water purification testing and guide, we made an exception for the MSR TrailShot Pocket-Sized Water Filter. This unique filter is compact, versatile, and effective, and it’s small enough for trail runners to carry. It can be used to drink directly from a creek or to refill water vessels on the go. And its design makes it effective for filtering shallow water, which is a huge plus if you’re venturing into the alpine where your water source might be a small, babbling stream. In addition, this aptly named filter can indeed fit easily into a hydration vest pocket. Like our other favorite water filters for trail running, it doesn’t require additional tools for cleaning — a few shakes will clear up a clogged filter and restore flow.

This filter has a few limitations, one being that it doesn’t double as a water bottle. It’s also on the heavier side, at 142 grams, compared to other filters designed for trail running. However, it’s quick to deploy without taking any lids on or off or screwing together any parts — simply pull it out of your pocket, drop the filter end into the cleanest water available, and give the little bottle some squeezes.

Depending on your hand and forearm strength, it can filter a liter of water in about 60 seconds. In testing, we found that it’s an ideal filter for refilling larger containers, like a one- to two-liter water bladder. It’s also a good filter option for group use since it’s quick to deploy and easy to operate.

Effective at Removing: Bacteria, protozoa, and sediment with a filter pore size of 0.2 micrometers (0.0002mm)

Water filters are a common solution for removing bacteria, protozoa, and sediment from water, but a purifier like the SteriPen Ultralight UV Water Purifier will inactivate all three classes of microorganisms: bacteria, protozoa, and viruses. It does so by using ultraviolet light to scramble the DNA of microorganisms in the water so that they cannot embed in your digestive system and reproduce, which is how they make you sick. In addition, this device is exceptionally small and light — weighing only 76 grams and measuring 5.1 inches in length. It’s comparable in size to a granola bar you might carry in your hydration vest. It’s also fast and can treat one liter of water in 90 seconds.

This device is simple and easy to use. Simply dip it into your water vessel so that the two metal sensors are submerged, then stir it slowly until the blinking green light turns solid green. The purifier will blink red and green when the battery is getting low, and since it’s rechargeable, all you need to do is plug it in before your next run so that it’s fully charged. A single charge will treat up to 20 liters of water, and the device will hold its charge for months.

This water purifier does have a few key limitations. For one, it requires clear water to be effective. This probably isn’t an issue if you’re running among fresh snowmelt runoff in the alpine — however, if your water source is cloudy or murky, you’ll need to pre-filter the water.

In addition, since it’s essentially a small lamp, you’ll want to be careful not to drop it — it will break more easily than some other types of purifiers. It also won’t work with small water bottles that don’t have a wide enough opening to allow stirring. Rather, this is ideal for individuals using a one-liter bladder or similar.

Effective at Removing: Bacteria, protozoa, cysts, and viruses using ultraviolet light

If you’re trail running with friends and want to carry one filter for the group, we recommend using the Platypus QuickDraw Microfilter System. The filtration system comes with a sturdy, yet collapsible, one-liter water bag and a separate hollow fiber filter that’s enclosed in a protective case. When it’s time to refill, start by filling the water bag from your nearest water source. After attaching the filter, turn it all upside down and squeeze the bag to help the water flow through the filter and into your water bottles or hydration reservoir. Be careful not to lose the small protective caps during the refilling process. Although it’s also possible to drink directly from the filter, this would not be practical while trail running since the water bag holds a full liter and would be cumbersome to carry by hand.

The system lives up to its name with an ultra-fast flow rate that filters a liter of water in 20 seconds. At 95 grams, it’s not the lightest system, though its multiple parts break down and the water bag rolls up to make it more packable. While it’s not the most compact and ultralight option available, the main draw of this system is its speedy filter rate. That’s why it’s a great option for a group — you can refill everyone’s bottles and reservoirs easily in a matter of minutes.

Effective at Removing: Bacteria, protozoa, and particulate with its filter pore size of 0.2 micrometers (0.0002mm)

While there are plenty of great water filters and purifiers available, it’s always good to carry a chemical backup option as well, such as Aquatabs Water Purification Tablets. These inexpensive tablets, which use sodium dichloroisocyanurate as the active ingredient, come in a pack of 30, and a single tablet can treat up to two quarts (1.89 liters) of clear water. A single tablet can also treat half as much cloudy water, though heavily sedimented water should be pre-filtered. Unlike other chemical water treatments, such as iodine, these tablets don’t change the taste or color of the water. As a result, it’s worth carrying a sleeve of these tablets in your first-aid kit or in a zipper pocket of your hydration vest, just in case your primary method for water purification fails.

These tablets are effective against bacteria, protozoa, and viruses. The only exception is the protozoa cryptosporidium — you’d need a filter or additional treatment to inactivate them. In addition, this treatment method won’t remove dirt, bits of moss, or other sediment — so, it’s better for use with clear water. Finally, the tablets take about 30 minutes to treat your water, so if you use this method while trail running, you’ll want to set a timer before sipping.

Effective at Removing: Protozoa, bacteria, cysts, and viruses using sodium dichloroisocyanurate

We love the Sawyer Mini Water Filtration System for trail running because it’s inexpensive, easy to use, and ultra-lightweight. At just 40 grams, it’s one of the lightest filtration systems on the market and the lightest in this guide. It’s also the least expensive, and at one point, it was probably one of the most popular water filtration systems among trail runners. Now there are a lot more options to suit a variety of needs and preferences, yet it remains a solid and reliable choice.

This system comes with a lightweight 16-ounce water bag and a small filter that measures 5.3 inches in length. To use, simply fill the bag with water, screw the filter onto the opening, turn the system upside down, and squeeze the bag. The filtered water will flow into your water bottle, reservoir, or mouth. While the system is straightforward, the bag also contains step-by-step instructions in case you forget. If the filter slows down or gets clogged, you can clean it by using the included syringe to backwash the filter, essentially pushing water backward through the filter to push gunk away from the fiber pores.

Effective at Removing: Bacteria, protozoa, and microplastics with its filter pore size of 0.1 micrometers (0.0001mm)

Water Filter: A water filter acts as a sieve and is effective at removing bacteria, protozoa, microplastics, sediment, and other particulate matter from water.

Water Purifier: A water purifier effectively inactivates all three classes of microbes: protozoa, bacteria, and viruses. Water purification uses ultraviolet light or chemicals to render microorganisms harmless.

Testing the LifeStraw Peak Series Collapsible Squeeze 650 ml Bottle with Filter in some spring runoff in Colorado. Photo: iRunFar/Eszter Horanyi

Sodium Dichloroisocyanurate: Sodium dichloroisocyanurate is a colorless water-soluble chemical made up of sodium, chlorine, carbon, nitrogen, oxygen, and hydrogen. It is used as a disinfectant for the purification of water and is the active ingredient in Aquatabs Water Purification Tablets. It is effective against the giardia parasite, but not cryptosporidium.

Bacteria: Bacteria are microscopic single-celled organisms found almost everywhere. While bacteria are vital to the planet’s ecosystems, certain types are harmful or deadly to humans. Escherichia coli (E. coli), Campylobacter jejuni, and Salmonella are a few examples of harmful bacteria that can be found in water.

Protozoa: Protozoa are single-celled organisms that can be free-living or parasitic, and they exist in most habitats worldwide. Giardia lamblia and Cryptosporidium are two parasitic protozoa found in water that can be very harmful to humans.

Virus: Waterborne viruses that infect humans come from human and animal feces in the water. The two most common waterborne viruses in North America are the rotavirus and the norovirus, which cause fever, vomiting, and diarrhea. In other parts of the world, other types of viruses may be more common in backcountry waters.

Cryptosporidium: Cryptosporidium is a microscopic parasite that causes the diarrheal disease cryptosporidiosis. Water, both drinking and recreational, is the most common way the parasite spreads. Due to its outer shell, “crypto” can survive for long periods of time outside of a host body and tolerate chlorine disinfection.

Water Purification: Filter Versus Treatment

A water filter is essentially a strainer with microscopic pores that removes sediment, microplastics, and microbes such as bacteria and protozoa from water. The smaller a water filter’s pore size, the more matter it will remove from the water.

However, because viruses are so tiny, they are generally not captured in a filter and need to be deactivated or killed by another purification method. Eventually, a water filter’s pores will become clogged, and the filter will need to be cleaned or replaced. We found that the best water filter for trail runners is the Katadyn BeFree 0.6L.

The Katadyn BeFree 0.6L is our favorite filter for trail runners because it combines the ability to filter water with an easy-to-use soft flask. Photo: iRunFar/Meghan Hicks

Water purifiers are required to meet federal standards for the inactivation of all three classes of microbes: protozoa, bacteria, and viruses. The SteriPen Ultralight UV Water Purifier is an example of using ultraviolet light to purify water. Other common purification methods include chemicals such as iodine, chlorine, or chlorine dioxide.

For trail runners, a water filter is going to be sufficient for most scenarios. However, if you’re running in an area where waterborne viruses are a risk, or you want added confidence in the safety of your drinking water, you could filter water and then treat it with one of the purification methods listed above.

Water filters are made with microscopic pores that only allow the tiniest particles through. Larger particles, such as bacteria and protozoa, will get caught in the fibers of the filter. The smaller the pore size, the more the filter will catch and eliminate from your drinking water. That said, smaller pores will also clog more quickly, requiring more frequent cleaning and filter replacement. Filtering from the cleanest possible water sources will help prolong the life of your filter.

All the filters on our list have a pore size of either 0.1 or 0.2 micrometers. A micrometer, often abbreviated as a micron, is one-millionth of a meter. There are 1,000 micrometers in a millimeter and 10,000 micrometers in a centimeter. For reference, the smallest objects that are visible to the naked eye are 40 to 50 micrometers.

So, yeah, these water filter pores are small! Small enough, in fact, to catch 99.9999% of bacteria and 99.99% of protozoa. Amazingly, viruses are even smaller than these organisms and can still make it through a water filter’s pores, which is why we rely on additional purification methods to inactivate viruses in our water.

Backwashing and Cleaning a Water Filter

Some water filters require periodic backwashing or other types of cleaning to help maintain a high flow rate. Backwashing is essentially pushing water backward through a filter to clear out the gunk that’s clogging the pores.

Some filters, such as the LifeStraw Peak Series Collapsible Squeeze 650 ml Bottle with Filter and the Sawyer Mini Water Filtration System, come with a syringe for backwashing the filter.

For other filters, like the Platypus QuickDraw Microfilter System, there are two methods for cleaning the filter, shaking or backwashing, that don’t require a syringe. Still others, including the MSR TrailShot Pocket-Sized Water Filter and the Katadyn BeFree 0.6L, can be easily cleaned at home or in the field with a shake or swish method.

It’s important to note that filters and the cartridges they’re housed in are delicate, and cleaning them improperly can cause permanent damage. For best results, we recommend following the instructions in the user manual that comes with your water filter.

Water Filter Storage and Care

For the best water filter storage and care, it’s important to follow the manufacturer’s instructions pertaining to your specific water filter. Before putting your filter into long-term storage, you’ll want to clean it first and allow it to dry completely. Store your filter away from direct sunlight and in a location where it won’t freeze.

LifeStraw recommends storing the LifeStraw Peak Series Collapsible Squeeze 650 ml Bottle with Filter in a saline solution made by mixing a teaspoon of salt with water. The solution helps to maintain the hydrophilic properties of the filter membrane while preventing mold and algae growth. Caring for your filter through proper cleaning and storage will help maintain its performance and extend its life.

Early season fastpacking in Colorado means you’ll want to carry a good way to purify your water. Photo: iRunFar/Eszter Horanyi

The iRunFar team is composed of road runners, trail runners, and ultrarunners with a collective 150-plus years of running experience. Several members of the team have been traveling in the backcountry and using water purification methods for over two decades.

We started this buyer’s guide with a deep dive into the water purification and treatment marketplace as well as the team’s previous experience and preferences with water purification methodology, narrowing our choices down to a list of the top filters and treatment options for trail runners.

From there, author Alli Hartz took our top choices into the field where she tested carrying and using them while running. Because this testing period overlapped with her trip to Ecuador, Alli tested a few of the filters in the waters near Quito and Cotopaxi National Park. The rest were tested along her home trails in central Oregon. This guide is a roundup of the top performers.

Why do you need purified water while trail running?

If it’s not clear from our glossary section above, there are some nasty types of bacteria, protozoa, and other organisms in lakes, rivers, streams, cow tanks, and puddles that can be harmful and even deadly to humans. The most common risk from drinking untreated water is some sort of bacterial or viral infection that will make you very sick — causing things like diarrhea, vomiting, headaches, and fever — which is certainly not a fun post-running experience and can lead to even less fun things like going to the hospital, experiencing long-term health effects, or dying.

While those cascading mountain streams and turquoise alpine lakes may appear innocuous, the fact is that any water source that has animal life nearby can contain microscopic organisms that can make humans very sick. Purifying water before drinking eliminates nearly all harmful substances and significantly reduces the risk of getting sick. Plus, water filters will catch dirt, tiny bits of moss, and other particulates so that your water tastes as pure as that mountain stream looks.

What type of water purifier is best for trail running?

The best purifier for trail runners is one that’s lightweight, compact, effective, easy to use, and quick. During long days on the trail, stopping to filter water can gobble up precious daylight — especially if it requires getting off the trail to access a good water source. Therefore, a water filter or purifier that’s easy to access and deploy is ideal.

This could be a filter that doubles as a water bottle, like the Katadyn BeFree 0.6L or the Salomon Soft Flask XA Filter.

For runners who prefer to run with a hydration bladder, the Sawyer Mini Water Filtration System may be a good option, since it’s super lightweight and can be used in line with a hydration bladder hose.

Or, if you know you’ll be near clear water, you may opt for SteriPen Ultralight UV Water Purifier, as it’s so lightweight, small, and quick.

Melissa Beaury (left) and iRunFar’s Meghan Hicks fastpacking in Utah’s canyon country. Meghan is carrying a Katadyn BeFree 0.6L in this image. Photo: iRunFar/Eszter Horanyi

When choosing the best water purification system for you, consider how you prefer to drink water on the trail — from small, soft flasks or from a bladder with a hose. Next, think about how you’ll carry the filter or purifier and what seems the most comfortable and convenient. Finally, consider which tool seems easy and intuitive to you.

While all the filters or purifiers on this list are relatively easy to use, some have more parts or require more steps to use. If you’re notorious for misplacing small components, opt for one that doesn’t have detachable parts. There are lots of good options out there, so once you’ve narrowed it down, go with your gut!

How safe are water filters for trail running?

Since water filters eliminate 99.9999% of bacteria and 99.99% of protozoa, they make water very safe to drink. The only microorganisms they don’t effectively remove are viruses. If you’re filtering water in an area where there could be harmful viruses in the water, then it’s a good idea to use a backup option like the SteriPen Ultralight UV Water Purifier.

What is the most effective water filter for trail running?

While there are no federal regulations for backcountry water filters, there are protocols and guidelines that filters should, and typically do, meet. You might come across phrases like “meets NSF Protocol P231” and/or “the U.S. Environmental Protection Agency’s Guide Standard and Protocol for Testing Microbiological Purifiers” on the water filter’s informational materials.

In addition, you’ll likely see specific claims, such as “removes 99.9999% of bacteria and 99.99% of protozoa.” This type of language indicates that the water filter is appropriate for the backcountry. Other numbers worth paying attention to are the filter’s pore size, which should be 0.1 or 0.2 micrometers — small enough to filter out bacteria and protozoa. All the filters on our list meet these standards and are effective and appropriate for trail running.

Aside from these minimum standards, the most effective water filter for trail running will be one that’s compact and comfortable to carry, easy to use, and durable. These factors will ensure that you carry and use your filter and don’t risk drinking straight from backcountry waterways.

What water filter removes the most contaminants?

As a rule of thumb, the water filter with the smallest pore size will remove the most contaminants from the water. That said, every filter on our list can remove 99.9999% of bacteria and 99.99% of protozoa. To ensure your water is as pure as possible, you could follow filtration with a water treatment method to take care of potential viral contamination.

How much water should I carry on a trail run?

This is a question that will depend on many factors as well as individual preferences. When planning for a long day on the trail and determining how much water to carry, two of the biggest variables to consider are the weather and how much water you’ll have access to on your route. You’ll need more water on a hot, dry day than on a chilly or rainy day.

At the same time, carrying a liter or more of water can feel heavy while running, so if you know you’ll have access to plenty of water, it may be worth carrying less and planning to stop and filter. That said, filtering takes time and breaks up the flow of the run.

After weighing all these factors, it’s a good idea to err on the conservative side and carry a bit more water than you think you’ll need as well as a filter in case you run out. The consequences of getting dehydrated or drinking unfiltered water are much worse than the burden of carrying a few extra ounces on your run.

This fastpacking campsite is looking glorious at sunset. Fastpacking trail runners should consider their best means of water purification in the backcountry. Photo: iRunFar/Eszter Horanyi

How do you know when it’s time to replace a water filter?

There are a few clues that will help you determine when it’s time to replace your filter. The biggest one will be when the flow rate slows down to an unbearable rate. The longevity of your filter will depend on the type of water you’re filtering.

However, don’t toss your filter just because it’s starting to slow down — trying cleaning it or backwashing it first. Your filter’s user manual will be a good reference for the best way to do this. If you’ve made some solid attempts at cleaning it and it’s still slow — and maybe you know you’ve been filtering some mucky water — then it may be time to consider replacing your filter. Depending on the model of your water filter, you may be able to replace the filter cartridge rather than the entire system.

Does altitude affect water filter flow rates?

Yes! Water filter flow rates tend to be slower at higher altitudes. If you’re heading up high, be sure your filter is clean and in good working condition before you go.

Can my water filter be frozen?

Freezing will damage most water filters, making them less effective. Give your filter’s user manual a careful read to see how freezing could affect its performance. For trail running, a frozen water filter is rarely going to be an issue. If you’re concerned about your filter freezing, consider carrying it close to your core and bringing a backup purification method, such as tablets.

Can my water filter withstand being dropped?

Generally, water filters are fragile and can be damaged by a hard drop. If you suspect you may have damaged your filter, look at the user manual — most have instructions for testing the integrity of your filter. That way, you’ll know for sure that it’s working properly before heading back into the field with it.

We want to hear about your favorite water purifier for trail running! Leave a comment to share which filter or treatment system you love and be sure to tell us in what conditions it performs best for you.

Alli Hartz is a member of the gear review team at iRunFar. She’s been writing about outdoor gear, outdoor adventure, and adventure travel for 10 years. Aside from iRunFar, Alli contributes gear reviews and adventure stories to Switchback Travel, Travel Oregon, and other outlets. She also works as a ski guide during the winter season and has dabbled in run-skiing on the Cascade volcanoes. Alli is based in Bend, Oregon, where she loves to run from her front door up into the Three Sisters Wilderness.