Best Water Filters for Trail Running of 2024

Numerous water purification methods can suit various needs and hydration preferences, but choosing the best water filter for trail running requires a few special considerations. Filters with built-in flasks are convenient for trail running because you can fill your soft flask and go without having to sit around filtering unless you need more than a flask of water. There are other filter options that work better if you’re filtering a large amount of water or filtering into a bladder.

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. Regardless of the type of water you’re filtering, you want to have confidence that it’s going to be safe to drink. We judged water filters on their flow rates, ease of use, and how they fit in a running pack. We also considered the types of contaminants that they could remove from the water.

Our team continues to turn to the original Katadyn BeFree 0.6L for our backcountry water filtration needs, though there are many similar filters new to the market that work very well too. When traveling in areas where we’re concerned about viruses in the water, we trust the SteriPen Ultralight UV Water Purifier to keep us safe and healthy. We also keep some Aquatabs 8.5mg Tablets X30 in all of our running packs for emergencies.

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.

Best Water Filters for Trail Running

• Overall Best Water Filter for Trail Running: Katadyn BeFree 0.6L
• Overall Best Water Filter for Trail Running — Runner-Up: HydraPak 42mm Filter Cap
• Overall Best Water Filter for Trail Running — Runner-Up: LifeStraw Peak Series Collapsible Squeeze 650 ml Bottle with Filter
• Overall Best Water Filter for Trail Running — Runner-Up: Salomon Soft Flask XA Filter 490ml/16oz 42
• Best Water Purifier for Trail Running: SteriPen Ultralight UV Water Purifier
• Best Water Filter For Trail Running for Group Use: Platypus QuickDraw Microfilter System
• Best Backup Water Treatment for Trail Running: Aquatabs 8.5mg Tablets X30
• Best Budget Water Filter for Trail Running: Sawyer Mini Water Filtration System

Overall Best Water Filter for Trail Running: Katadyn BeFree 0.6L ($39)

Pros:

• Compact
• Lightweight
• Easy to use

Cons:

• The flask can spring leaks

There’s a good reason the Katadyn BeFree 0.6L is wildly popular among trail runners. It’s small, lightweight, compact, and reliable. It was also the original filter that fit directly onto a soft flask for ease of use on the trail. The filter and soft flask weigh just 59 grams and measure about 4.3 inches in length, including the lid. The soft flask of this filter is just slightly bigger than other 500- to 550-milliliter ones — and it can be squeezed into the pocket of most hydration vests, though it can feel a bit bulky and floppy. Depending on your filtering needs, this filter is available with both a 0.6- and one-liter flask. The filter can also fit on any HydraPak soft flask, so you can use it with the one that fits your hydration vest the best.

The ease of use of this filter also sets it apart from its competitors. To operate, unscrew and remove the lid containing 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 are needed; just swish or shake the bottle with clean water.

Unfortunately, this filter can and will clog with use, even with regular swishing and cleaning. As the filter clogs, the flow rate will slow. When it gets to an unbearably slow flow, it means it’s time to replace the filter, not because it’s less effective at removing contaminants, but because you don’t want to spend all day sitting next to a creek filtering water when your running companions are fully hydrated and ready to go. That said, with regular cleaning, these filters last long enough and work so well that we justify replacing them occasionally.

We found that the soft flask that comes with the filter will get pinhole leaks if not treated with care. You can also buy just the filter part of this package if you already have soft flasks that it will fit.

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)

Shop the Katadyn BeFree 0.6L

Overall Best Water Filter for Trail Running — Runner-Up: HydraPak 42mm Filter Cap ($35)

Pros:

• Lightweight
• Easy to use
• High flow rate

Cons:

• Clogs eventually
• It doesn’t come with a soft flask

If you already own HydraPak soft flasks and want to avoid buying a filter that comes with one, you can get just the HydraPak 42mm Filter Cap. Before you could buy the Katadyn BeFree filter without the flask, this was a bigger deal, as it would save you money. Still, this great little filter allows you to customize the flask size you want to use with it.

The filter is easy to use; simply fill any 42-millimeter diameter HydraPak soft flask with water, thread the filter on, and drink. You can also use this system to fill other water containers. With an initial filtration rate of over a liter per minute, you can filter a lot of water quickly, or you can sip easily directly from the filter and not experience very much resistance at all. The flow rate is high enough that we were never annoyed with having to drink from it, and sometimes, it seems like the water isn’t going through a filter at all. But it is! And the 0.2-micrometer filter removes 99.99% of E. Coli and parasitic cysts.

The 57-gram filter is light and on par with similar-style filters and will fit onto any 42-millimeter diameter HydraPak flask. It has a cover for the nozzle to keep water from leaking out and protect the mouthpiece from dust and other contaminants. We appreciated the cover since we often found ourselves putting the filter on the ground while we went down to the water to fill a flask.

Flow rates were nearly identical in initial side-by-side tests with the BeFree filter reviewed above. A pair of our iRunFar testers had these two filters for the summer and used them about the same amount. While they didn’t go on identical trips, their overall use was fairly similar. By the end of summer, this filter was flowing just slightly better, but the difference was small enough that we can’t say if it was due to variations in use or because the filter clogged less easily. Either way, this filter performs up there with the best comparable option and is easy to clean by swishing it around in clean water.

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

Shop the Katadyn BeFree 0.6L

Overall Best Water Filter for Trail Running — Runner-Up: LifeStraw Peak Series Collapsible Squeeze 650 ml Bottle with Filter ($38)

Pros:

• High flow rate
• A removable filter enhances packability
• The filter is compatible with other LifeStraw Peak Series systems

Cons:

• Relatively heavy
• Nearly opaque soft flask hides water amount

With a similar design and operation to our other top soft-flask filter choices, the LifeStraw Peak Series Collapsible Squeeze 650 ml Bottle with Filter receives the runner-up award only because it’s slightly heavier and bulkier at 102 grams. 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 if you’re tight on space.

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, a plastic case houses the filter, which adds weight but protects the filter’s delicate fibers.

Because the 650-milliliter soft flask is dark, it’s tricky to see how much water you have unless you hold it up to the light. If you tuck your bottle into a hydration vest pocket, it may not be apparent when running low on water. However, because of the bottle’s size and shape and the fact that it doesn’t fit into most hydration vest pockets super well, trail runners will be likelier 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.

Read more in our in-depth LifeStraw Peak Series Collapsible Squeeze 650 ml Bottle with Filter review.

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

Shop the LifeStraw Peak Series Collapsible Squeeze 650ml Bottle with Filter

Overall Best Water Filter for Trail Running — Runner-Up: Salomon Soft Flask XA Filter 490ml/16oz 42 ($50)

Pros:

• Lightweight
• Compact
• High flow rate

Cons:

• You have to squeeze the mouthpiece to filter water into another container, risking contamination
• No protective cover for the nozzle
• Limited capacity

Although it has some limitations, the Salomon Soft Flask XA Filter 490ml/16oz 42 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 of liquid. Its long cylindrical shape is designed to fit Salomon vests and will slide into the front pocket of most hydration vests. The hollow fiber filter is about 4.5 inches long and will fit any HydraPak soft flasks, excluding those with a narrow mouth opening.

The hard plastic loop on the filter makes it easier to hold while filling it up and putting the lid back on. To operate the filter, simply fill the soft flask with water and either drink directly from the mouthpiece 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. Of all the filter nozzles, this one most closely mimicked a normal soft-flask mouthpiece.

The only real downside of this filter is that, unlike most other filters in this guide, the nozzle has no cover to protect it from being splashed by contaminated water. 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. That said, it’s the easiest to drink out of since there’s no lid to remove before using.

Effective at removing: Bacteria and protozoa

Shop the Salomon Soft Flask XA Filter

Best Water Purifier for Trail Running: SteriPen Ultralight UV Water Purifier ($125)

Pros:

• Great for travel since it works against both bacteria and viruses
• Rechargeable
• Fast

Cons:

• Requires clear water to be effective
• It is more fragile than other types of filters
• Won’t work for soft flasks with small openings
• Expensive

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 also be effective against viruses, which are generally too small for a normal filter to remove. It does so by using ultraviolet light to scramble the DNA of microorganisms in the water so that they cannot reproduce if they end up in your digestive system, which is how they make you sick. This device is incredibly light and compact at just 76 grams and measures 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. It doesn’t remove sediment or other floaties from the water, so you’ll probably want to pre-filter your water if there is sediment or organic matter in it.

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 in the mountains — 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 other purifiers. It also won’t work with small water bottles that don’t have a wide enough opening to allow stirring. Instead, this is ideal for individuals using a one-liter bladder or a hard-sided water bottle with a wide opening.

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

Shop the SteriPen Ultralight UV Water Purifier

Best Water Filter for Trail Running for Group Use: Platypus QuickDraw Microfilter System ($55)

 Pros:

• Ultra-fast flow rate
• Durable
• Ideal for group use

Cons:

• Relatively heavy
• Multiple parts
• A water storage bag is not a practical drinking vessel while running

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 has a sturdy one-liter water bag that rolls up fairly small when not used and a separate hollow fiber filter enclosed in a protective case. When it’s time to refill water, fill the bag from your nearest water source. After attaching the filter, turn it 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 high flow rate of 20 seconds per liter makes this an excellent choice when you have to filter a lot of water at once. At 95 grams, it’s not the lightest system, though it’s not heavy by any stretch, and its multiple parts break down so you can share the weight among a group. You’ll also have to carry a second bottle that is easier to drink from while running when using this system.

While it’s not the most compact and ultralight option available, the main draw of this system is its speedy filter rate — you can refill everyone’s bottles and reservoirs easily in minutes.

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

Shop the Platypus QuickDraw Microfilter System

Best Backup Water Treatment for Trail Running: Aquatabs 8.5mg Tablets X30 ($15 for 30 pack)

Pros:

• Lightweight and packable
• It doesn’t alter the taste of water

Cons:

• Requires a 30-minute wait before drinking
• It doesn’t filter out sediment
• Not effective against Cryptosporidium

While plenty of great water filters and purifiers are available, carrying a chemical backup option, such as Aquatabs 8.5mg Tablets X30 is always a good idea. 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, even if only with a shirt or bandana in a pinch. Unlike other chemical water treatments, such as iodine, these tablets don’t change the taste or color of the water. Even if you’re not planning on picking up extra water on your run, it’s not a bad idea to carry a few of these tablets whenever you head out, just in case something goes wrong and you need extra drinking water.

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 it. 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 purify 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

Shop the Aquatabs Water Purification Tablets

Best Budget Water Filter for Trail Running: Sawyer Mini Water Filtration System ($25)

Pros:

• Easy to use
• Compact
• Ultra-lightweight

Cons:

• Multiple parts
• A water storage bag is not a practical drinking vessel while running

We love the Sawyer Mini Water Filtration System for trail running because it’s inexpensive 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. Even with many other options, this filtration system remains a favorite for trail runners and thru-hikers because it can be cleaned by backflushing the filter with the included syringe. This makes it last longer than many of the filters that attach directly to soft flasks and don’t have a backwashing option.

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 bag has quite a small opening and can be difficult to fill with water, especially if you’re trying to fill it from a lake or other body of standing water. Patience is key, and some people will carry a second small container to scoop water into the bag. Once the filter is attached to 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.

You can also use this filter in-line with a bladder. If you prefer to carry a bladder instead of soft flasks when you run, this is a great filtration option as you can simply fill up your bladder with the filter attached to the hose and keep running.

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

Shop the Sawyer Mini Water Filtration System

Comparing the Best Water Filters for Trail Running

WATER FILTER	PRICE	CAPACITY	WEIGHT
Katadyn BeFree 0.6L	$39	20 ounces (600 milliliters)	2 ounces (57 grams)
HydraPak 42mm Filter Cap	$35	N/A	2 ounces (57 grams)
LifeStraw Peak Series Collapsible Squeeze 650 ml Bottle with Filter	$38	22 ounces (650 milliliters)	3.2 ounces (91 grams)
Salomon Soft Flask XA Filter 490ml/16oz 42	$50	16 ounces (490 milliliters)	Not listed
SteriPen Ultralight UV Water Purifier	$125	N/A	2.7 ounces (77 grams)
Platypus QuickDraw Microfilter System	$55	34 ounces (1 liter)	3.3 ounces (94 grams)
Aquatabs 8.5mg Tablets X30	$15	N/A	Not listed
Sawyer Mini Water Filtration System	$25	16 ounces (490 milliliters)	2 ounces (57 grams)

Water Purification Glossary

Water Filter: A sieve for particles in the water that effectively removes bacteria, protozoa, microplastics, sediment, and other particulate matter.

Water Purifier: A system using ultraviolet light or chemicals to inactivate all three classes of microbes: protozoa, bacteria, and viruses.

Sodium Dichloroisocyanurate: A colorless, water-soluble chemical comprising sodium, chlorine, carbon, nitrogen, oxygen, and hydrogen. It is a disinfectant and the active ingredient in Aquatabs 8.5mg Tablets X30. It is effective against the giardia parasite but not Cryptosporidium.

Bacteria: 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 harmful bacteria in water.

Protozoa: Single-celled organisms that can be free-living or parasitic and exist in most habitats worldwide. Giardia lamblia and Cryptosporidium are two parasitic protozoa found in water that can harm 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 and are relatively rare in backcountry waters. In other parts of the world, other types of viruses may be more common in the water

Cryptosporidium: A microscopic parasite found in water that causes the diarrheal disease cryptosporidiosis. Due to its outer shell, “crypto” can survive for long periods outside a host body and tolerate chlorine disinfection.

How to Choose a Water Filter for Trail Running

Water Purification: Filtering Versus Purification

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. When choosing the best water filter for trail running, you’ll want to select one with a pore size of either 0.1 or 0.2 micrometers.

Because viruses are so tiny, they can move through a filter and must be deactivated by either chemicals or UV light. Eventually, a water filter’s pores will become clogged, and the filter will need to be cleaned or replaced. The best water filter for trail runners is the Katadyn BeFree 0.6L because of its light weight and ease of use. We also loved the HydraPak 42mm Filter Cap.

Water purification systems must meet federal standards for the inactivation of all three classes of microbes: protozoa, bacteria, and viruses. The SteriPen Ultralight UV Water Purifier uses ultraviolet light to purify water. Chemical purification methods, such as iodine, chlorine, or chlorine dioxide, are also common.

For trail runners, a water filter will 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, either chemical or UV.

Water Filter Pore Size

Water filters have microscopic pores that stop nearly all particles. Viruses are small enough to fit through even the smallest pores found in common filters. Larger particles like bacteria and protozoa will get caught in the filter’s fibers. 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. Regular cleaning, whether using the swishing method for the Katadyn BeFree 0.6L or the Salomon Soft Flask XA Filter 490ml/16oz 42 or backflushing the Sawyer Mini Water Filtration System will also extend the lifespan of your water filter.

All the filters on our list have pore sizes of 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 visible to the naked eye are 40 to 50 micrometers.

So, yeah, these water filter pores are tiny! Small enough, in fact, to catch 99.9999% of bacteria and 99.99% of protozoa. Water filters will have their efficacy rates printed on their packaging. If you’re concerned about viruses in your water, you’ll want to use an additional purification method like Aquatabs 8.5mg Tablets X30 to inactivate viruses as well.

Backwashing and Cleaning a Water Filter

Water filters require periodic backwashing or other types of cleaning to maintain a high flow rate. Backwashing is pushing water backward through a filter to clear out the gunk 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. Cleaning a filter regularly will help maintain its flow rate and extend its lifespan.

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. 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 housing them are delicate, and cleaning them improperly can cause permanent damage. For best results, we recommend following the cleaning instructions included in the user manual.

Water Filter Storage and Care

For the best water filter storage and care, follow the manufacturer’s instructions for your specific filter. Before storing your filter long-term, clean it 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 salt with water. The solution helps maintain the filter membrane’s hydrophilic properties while preventing mold and algae growth.

Why You Should Trust Us

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

We started this buyer’s guide with a deep dive into the water purification and treatment marketplace and the team’s experience and preferences with water purification methodology, narrowing our choices to a list of the best water filters for trail running.

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. Alli tested the rest along her home trails in central Oregon. This guide is a roundup of the top performers. We have since updated this guide with updated products and additional testing insights, including tests in the Rocky Mountains and the American Southwest.

Frequently Asked Questions About Water Purification for Trail Running

Why do you need purified water while trail running?

Some nasty types of bacteria, protozoa, and other organisms in lakes, rivers, streams, cow tanks, and puddles 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 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 illness. Plus, water filters will catch dirt, tiny bits of organic matter, and other particulates, so your water tastes as pure as that mountain stream looks. And when the best water filters for trail running options are as light, fast, and as easy to use as the Katadyn BeFree 0.6L or the HydraPak 42mm Filter Cap, there’s no reason not to carry one.

What type of water purifier is best for trail running?

The best water cleaning system for trail runners is lightweight, compact, effective, easy to use, and quick. It can either be a filtration system or a chemical or UV light purification system. During long days on the trail, stopping to filter water can gobble up precious time. Therefore, a water filter or purifier that’s easy to access, deploy, and fast to use is ideal.

Filters that attach directly to a soft flask, like the Katadyn BeFree 0.6L or the Salomon Soft Flask XA Filter 490ml/16oz 42, are quick and effective because all you have to do is fill up your flask from a water source, screw on the filter cap, and keep going, drinking directly from the filter mouthpiece as you run.

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 works with a hydration bladder hose.

Or, if you know you’ll be near clear water, you may opt for the SteriPen Ultralight UV Water Purifier, as it’s so lightweight, small, and quick. They are also a great option if you’re traveling in an area where waterborne viruses are more common and you want the best protection possible.

When choosing the best water filtration or purification system, consider how you prefer to drink water on the trail — from smaller soft flasks or a bladder with a hose. Next, consider how you’ll carry the filter or purifier and what seems the most comfortable and convenient. From there, you can choose the tool that 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. If you’re notorious for misplacing small components, opt for one that doesn’t have detachable parts. There are many good options for the best water filter for trail running, so once you’ve narrowed it down, go with your gut!

Do I have to filter all backcountry water?

Not all backcountry water has harmful bacteria; generally speaking, the more remote a water source, the less chance that it will have giardia or other microbes that will make you sick. We’ve watched friends drink directly from manky desert potholes and suffer no ill effects, and we’ve also (accidentally) filtered water contaminated by mine waste and spent the night and the next day huddled next to the toilet. All this to say, drinking unfiltered wild water can be perfectly fine, and filtering water won’t always prevent a date with the porcelain throne.

Our team, which has consumed thousands of liters of wild water throughout the world, most of it filtered and some of it not, still errs on the side of using filters all the time. When you have lightweight options like the Katadyn BeFree 0.6L or the Salomon Soft Flask XA Filter 490ml/16oz 42, it really feels like a no-brainer for us to gain that extra bit of peace of mind when drinking wild water.

We recommend filtering everything you drink if there are cows or other domesticated livestock around.

How safe are water filters for trail running?

Since water filters remove 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 with harmful viruses, then using a water purification device like the SteriPen Ultralight UV Water Purifier is a good idea.

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 find 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 backcountry use. 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 adequate and appropriate for trail running.

Aside from these minimum standards, the best water filter for trail running will be compact, comfortable to carry, easy to use, and durable. These factors ensure you carry and use your filter and don’t risk drinking straight from backcountry waterways because your filter is too inconvenient to carry. Pairing a water filter like the Salomon Soft Flask XA Filter 490ml/16oz 42 with a water purification method like the SteriPen Ultralight UV Water Purifier will all but ensure that your water is safe to drink wherever you’re picking it up from.

How much water should I carry on a trail run?

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

Carrying a liter or more of water can feel heavy while running, so if you know you’ll have access to plenty of water while out on the trail, 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. Having a sleeve of Aquatabs 8.5mg Tablets X30 in your pack at all times can provide a safety backup in case something goes wrong, and you run out of water unexpectedly.

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

A few clues will help you determine when it’s time to replace your filter. In most cases, it will be when the flow rate slows to an unbearable rate. The longevity of your filter will depend on the type of water you’re filtering. Most water filters will advertise the number of liters of water they will filter over the course of their lifespan, but in our testing, none of them actually get near that number before they start to clog and slow down.

However, don’t toss your filter just because the flow rate is decreasing — try cleaning or backwashing it first. Cleaning the filter of the Katadyn BeFree 0.6L regularly by swishing it around in clean water can keep it flowing efficiently for a long time. You’ll be surprised by the number of particles that come out of it if you do it in a glass of water! Your filter’s user manual will be a good reference for the best way to clean it. If you’ve made some solid attempts at cleaning it and it’s still slow — and maybe 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.

What happens if my water filter freezes?

Freezing will damage most water filters, especially if they’re wet, and can make them less effective. If you think your water filter is frozen, let it thaw before trying to use it to minimize the damage. Give your filter’s user manual a careful read to see how freezing could affect its performance. For most trail running situations, a frozen water filter is rarely going to be an issue, but if you’re fastpacking, you might want to sleep with your water filter in your sleeping bag if the night is going to get below freezing. If you’re concerned about your filter freezing, consider carrying it close to your core and bringing a backup purification method, such as Aquatabs 8.5mg Tablets X30.

How durable are the water filter flasks?

Most flasks that come with water filters are comparable to those made by regular running brands, and Hydraflask makes many of them. They can withstand the regular wear and tear of being in a running vest or fastpacking pack pocket, but they will spring leaks on occasion. Many of the filters included in this guide, including the Katadyn BeFree 0.6L, will screw onto any HydraPak soft flask if the original one gets damaged.

Call for Comments

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 tell us in what conditions it performs best for you.

• Do you have a favorite water filtration or purification system that you use?
• Do you regularly filter water while you’re out on your runs?

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