Everyone exploring the backcountry needs water, but staying hydrated is not as simple as drinking straight from streams and lakes. To protect against protozoa, bacteria, and even viruses, there is a wide range of water filtration and purification systems built specifically for backpacking (many options on this list are great for day hiking, trail running, and travel too). Our top picks for 2018 below include everything from ultralight straw filters and chemical drops to pumps and large-quantity gravity filters. For more background information, see our water filter/purifier comparison table and buying advice below the picks. 

1. Platypus GravityWorks 4L ($120)

Platypus GravityWorks 4L filterType: Gravity filter
Weight: 11.5 oz.
Filter life: 1,500 liters
What we like: Filters and stores a high quantity of water effortlessly and quickly; great for groups.
What we don’t like: Bulky and you need a decent water source to fill the bag.

Without a doubt, the Platypus GravityWorks is one of the most convenient water filters on the market, and it’s become a backpacking staple. Instead of pumping, this system requires minimal effort, can filter up to four liters of water at once, and boasts a speedy flow rate of 1.75 liters per minute. Gravity does all the work: simply fill up the 4-liter “dirty” reservoir, hang it from a tree branch or boulder, and in just a few minutes you’ll have four liters of clean water to drink. This filter is great for large groups, but we’ve enjoyed it on smaller outings too when we could quickly retrieve our day’s water and escape back to our camp to fill individual bottles (the clean bag also functions as water storage).

Compared to some of the more minimalist options below, the Platypus GravityWorks is not a small apparatus, with two bags, a filter, and a bundle of tubing. More, water retrieval can be a pain if you don’t have a reasonably deep or moving water source (similar to any system that relies on a bag to collect water). And at $120, the GravityWorks is at the more expensive end of the water filtration spectrum. But we love the convenience, especially for groups of backpackers or basecamp-type situations, and feel it’s worth the cost and bulk... Read in-depth review
See the Platypus GravityWorks 4L


2. MSR Guardian Purifier System ($350)

MSR Guardian water purifierType: Pump purifier
Weight: 17.3 oz.
Filter life: 10,000 liters
What we like: The most advanced portable water purifier on the market.
What we don’t like: At $350, the Guardian is the priciest option on this list.

We’ll start by acknowledging the steep $350 price tag of the MSR Guardian, but this pump is the real deal. Most importantly, it’s both a water filter and purifier, adding ever-important virus protection to the mix. Whereas other pumps from Katadyn and MSR only protect against protozoa and bacteria, the Guardian provides the ultimate piece of mind when backpacking in high-use areas (viruses are most commonly carried in human waste). In fact, it’s such a reliable and convenient system that it’s now being used as an emergency water purifier after natural disasters and in less-developed countries around the world.

Aside from cost, the MSR Guardian is not a small or light system. At just over 17 ounces and packing down roughly to the size of a 1-liter water bottle, this is much more pump than its non-purifying siblings. But it’s head and shoulders above the competition in performance and build quality. Not only does it boast advanced self-cleaning technology (the Guardian uses about 10% of the water from every pump to flush contaminants), it’s far less likely to break down than cheaper models. In terms of whether or not you need the purifying capabilities: it’s certainly smart for travel and backpacking in less-developed regions of the world. In Peru, we pumped and drank water from a creek where a full cow skeleton had come to rest and did not get sick. Viruses certainly are less of a risk in the North American and European backcountry, but as the saying goes, it’s better to be safe than sorry. 
See the MSR Guardian Purifier System


3. Sawyer Squeeze Water Filter ($40)

Sawyer Squeeze water filterType: Straw/gravity filter
Weight: 3 oz.
Filter life: 1 million gallons
What we like: Super lightweight, fast flow rate, and long lasting.
What we don’t like: More effort than gravity filter and some pump systems.

The Sawyer Squeeze epitomizes ultralight water treatment and has been a mainstay for years. At just 3 ounces, it provides filtered water as fast as you can, well, squeeze. The system works by filling the included 32-ounce pouches with dirty water, then squeezing them into a clean bottle or reservoir, a pot for cooking, or straight into your mouth. For those moving fast and light, it’s a simple option for day hiking and backpacking, provided you know the location of river crossings or other water sources (or carry bottles along for storage). And with a 1-million-gallon guarantee, Sawyer doesn’t even make replacement cartridges for this filter.

This streamlined water filtration does have downsides. First and foremost, as with the GravityWorks above, collecting water with the included pouches can be a pain if your source is too shallow or not moving quickly. Second, squeezing a liter of water ends up being more effort than letting a gravity filter do the work or even compared with some of the more efficient pump systems (Sawyer does include an adapter for converting the Squeeze into a gravity filter). The Sawyer system does come in a “Mini” version described below, which is just 2 ounces and $25 but isn’t as impressive in terms of flow rate and overall performance.
See the Sawyer Squeeze Water Filter


4. Katadyn Hiker Pro Microfilter ($85)

Katadyn Hiker Pro water filterType: Pump filter
Weight: 11 oz.
Filter life: 750 liters
What we like: A versatile and reliable that can make clean water from puddles.
What we don’t like: Relatively short filter life and pricey to replace.

Pumping water has its downsides, but we’ve found that the Katadyn Hiker Pro is one of the most reliable filter options across a wide range of backpacking scenarios. Simply put, you break out your Hiker Pro, place the hose end in the water, screw the other end onto your Nalgene (or hold it over top if you have a different type of bottle or reservoir), and pump. You get roughly one liter of clean water per minute if you’re pumping at a good clip, and we’ve found that the Hiker Pro works faster and is easier to use than the MSR MiniWorks below. Unlike the MSR Guardian, however, the Hiker Pro is a filter but not a purifier, so you don’t get virus protection.

In terms of construction, the Katadyn Hiker Pro is well built for a pump but these systems are not infallible. The device is made of ABS plastic and has a number of hoses and small parts, and we’ve had pieces snap off of other pumps in the past (not with the Katadyn yet, but it certainly can happen). Another downside is the rather pricey replacement filter: after approximately 750 liters, you’ll need to spend $50 for a new one (the MSR MiniWorks recommends a replacement filter after 2,000 liters and that costs $40). But we still prefer the Katadyn, which despite the shorter filter life, has faster and smoother pumping action.
See the Katadyn Hiker Pro Microfilter


5. Aquamira Water Treatment Drops ($15)

Aquamira Water Treatment DropsType: Chemical purifier (drops)
Weight: 3 oz.
Shelf life: 4 years
What we like: Lightweight, cheap, and protects against viruses.
What we don’t like: Despite being safe, you’re drinking unfiltered water straight from the source.

We used to use tablets as backup in case our pump broke, but Aquamira has changed the equation. At just 3 ounces total for 2 treatment bottles, the process is as follows: you mix 7 drops of each in the included plastic cup, wait 5 minutes until the mixture turns yellow, pour it into 1 liter of water, and wait 15 minutes (or double the dose and wait time if the water is super cloudy or cold). Unlike iodine tablets, these Chlorine dioxide drops kill viruses for full purification. At just $15, that’s a pretty darn attractive backpacking solution.

All things considered, we love the simplicity and cost effectiveness of this system. The majority of options on the list are filtration only, but the Aquamira Drops provide purification for a fraction of the price of a system like the MSR Guardian. The biggest downside of any drop or tablet solution is that despite the purifications, you’re drinking the water unfiltered out of the source (in Utah, for example, that may mean brown water with lots of critters). But if you have ample water sources that aren’t stagnant, Aquamira Drops are a great ultralight option. A final note: Aquamira recommends waiting 4 hours to kill Cryptosporidium, a specific type of Protozoa, which obviously is a very long time.
See the Aquamira Water Treatment Drops


6. Katadyn BeFree Collapsible Bottle 1L ($45)

Katadyn BeFree Collapsible water filter bottleType: Straw filter
Weight: 2.3 oz.
Filter life: 1,000 liters
What we like: Extremely light and great for on-the-go hydration.
What we don’t like: Less versatile than the Sawyer Squeeze.                                                                                                      

The ultralight water filter market is expanding, evidenced by the relatively new Katadyn BeFree and MSR TrailShot. Designed to go head-to-head with the popular Sawyer Squeeze above, the BeFree is another solid option in this category. Instead of squeezing, you drink directly from the ultralight straw filter. Compared to the Sawyer, the Katadyn is lighter at just 2.3 ounces, more packable, easier to use, easier to clean, and has a wider mouth from which to fill. This feature set makes the Katadyn a nice choice for trail runners, mountain bikers, and day hikers.

Why is the Katadyn BeFree ranked here? First, it has a relatively short lifespan compared to the Squeeze (1,000 liters vs. a claimed 1 million gallons). Second, the BeFree filter only is compatible with bottles with a 42mm mouth, so it’s not as easily replaceable as the Sawyer which fits a variety of standard 28mm water bottles. Third, we definitely noticed a faint plastic taste when using the bottle, which has been the case with other Hydrapak products as well (the bottle is BPA free, but nobody wants their water to taste like plastic). Finally, the Katadyn is $5 more plus the potential cost of a new filter ($25) and lacks the versatility of the Sawyer’s gravity adapter. But the BeFree wins out for ease of use, and its lightweight and compressible design earns it a spot on our list.
See the Katadyn BeFree Collapsible Bottle 1L


7. MSR AutoFlow 2L ($110)

MSR AutoFlow Gravity Filter 2LType: Gravity filter
Weight: 10 oz.
Filter life: 1,500 liters
What we like: Like the Platypus GravityWorks above, this system is almost effortless.
What we don’t like: We prefer the two-bag system of the Platypus for storage and ease of maintenance.

Similar to the Platypus GravityWorks above, the MSR AutoFlow is a gravity filter system that does the work for you. You simply scoop water from your source, hang it from a branch or large rock, and wait while the filter completes the rest. Like the Platypus, the AutoFlow boasts an easy shut-off system, lightweight design, and fast flow rate of 1.75 liters per minute. Because you can have multiple liters of clean water within just a few minutes without pumping or drinking silt, gravity filters are our favorite overall design for backpacking.

What differentiates the MSR AutoFlow from the Platypus GravityWorks? First and foremost, the MSR is a one-bag design, meaning that it comes with a bag for dirty water but you filter directly into your water bottle or reservoir (we prefer the Platypus in this regard for its easy dispensing and storage). And because it’s a one-bag system, backflushing can be more complicated, and particularly if you’re not storing water in an MSR-compatible bladder. Finally, if you do decide to go with a bladder for clean water, or a dromedary as MSR calls them, it will come at an extra cost: $40 for the 4-liter version, for example. We are fans of the AutoFlow design, but it happens to fall short of the more complete GravityWorks system.
See the MSR AutoFlow 2L


8. SteriPen Adventurer Opti ($90)

SteriPen Adventurer Opti UV purifierType: UV purifier
Weight: 3.8 oz.
Lamp life: 8,000 liters
What we like: Lightweight and inexpensive purification.
What we don’t like: Relies on batteries/USB charge.

For more than 15 years and counting, SteriPen has held a unique place in the water purification market. Instead of the various gravity filters, pumps, and drops on this list, the Adventurer Opti uses UV rays to destroy bacteria, protozoa, and viruses—a full purification process at less than 4 ounces total for the unit. It takes about 90 seconds to purify 1 liter of water: you simply place the SteriPen in your water and swirl until the light turns green. Keep in mind that the SteriPen goes directly into your bottle—the water will remain unfiltered and therefore you’ll want a good water source.

We love the concept of the SteriPen, but have mixed feelings after extended use. The lack of filtration certainly is a downside, and means that unless you don’t mind silt and other particles, you’re limited to moving water sources of a decent depth. Second, the SteriPen runs on two CR123 batteries, and if those run out and you don’t have backup, you’re stuck in the wilderness with no purification. Finally, when using the SteriPen, we just can’t help but feel like we are doing something wrong. Did we submerge the device too little or too much? Is the process actually working? These are just our insecurities and we’ve never been sick after using a SteriPen, but it is something that comes to mind. For those who prefer USB charging, the SteriPen Ultra weighs 5 ounces total including a rechargeable battery and costs $100.
See the SteriPen Adventurer Opti


9. MSR TrailShot Water Filter ($50)

MSR Trailshot water filterType: Pump filter
Weight: 5 oz.
Filter life: 2,000 liters
What we like: The smallest and lightest pump filter available.
What we don’t like: Other options serve the same fast-and-light purpose.

At a weight that’s half of MSR’s AutoFlow above and size small enough to fit in your pocket, the new TrailShot is a great on-the-go filtration system for trail running and day hiking. This minimalist, one-handed pump allows you to filter water without laying on the ground (such as with the LifeStraw) or getting cold hands by filling up and squeezing bottles (such as with the Sawyer Squeeze or Katadyn BeFree). Additionally, it works well in shallow pools or streams, which is a weak point of many squeeze and gravity systems. And with the ability to filter about 1 liter per minute, the TrailShot keeps up with the competition in terms of speed.

Despite weighing only 5 ounces, the MSR TrailShot is among the heaviest of the ultralight filters on this list. Additionally, it’s somewhat slow to use compared to more serious pumps, particularly in dirty water, meaning that it should not be your primary option on full-on backpacking trips (and especially in a group). Overall, we think that other products above like the Sawyer Squeeze serve the fast-and-light functions better, but if you’re a fan of pump filters and looking for a lightweight option, the TrailShot is a nice choice.
See the MSR TrailShot Water Filter


10. LifeStraw Water Filter ($20)

LifeStraw Water FilterType: Straw filter
Weight: 2 oz.
Filter life: 4,000 liters
What we like: Great as an emergency backup or if you’re truly counting every ounce.
What we don’t like: Cannot fill bottles and requires getting down at water level to drink.

The LifeStraw fills yet another niche: direct water-to-mouth filtration. Using this straw is as easy as it gets: insert one end into a body of water (or a bottle that you’ve filled with unfiltered water), and drink away from the other. The LifeStraw weighs just 2 and maintenance is simple—just blow back through the straw to clear it. And at $20, it’s as cheap as filters get (a more durable steel version is available for $55, but that seems like overkill and more weight to us). In terms of uses, the LifeStraw makes a great backup in case your filter breaks and is an ultralight option for day hiking and trail running.

The big downside of the LifeStraw is that it cannot be used to fill bottles and therefore is not a plausible filtration system for backpacking or group settings. And unless you’re trying to go as streamlined as possible, there aren’t many situations where you’d choose the LifeStraw over the convenience of the Sawyer Squeeze, Katadyn BeFree, or droplets. In addition, using the LifeStraw means getting down on the ground just a few inches from your pool of water to drink, the novelty of which wears off rather quickly. But you can’t knock the weight, price, or simplicity, which is why the LifeStraw is a viable filtration option.
See the LifeStraw Water Filter


11. MSR MiniWorks EX ($90)

MSR MiniWorks EX water filterType: Pump filter
Weight: 16 oz.
Filter life: 2,000 liters
What we like: One of the few pump designs with a ceramic filter.
What we don’t like: Heavier and slower than the Katadyn Hiker Pro.

Despite all of the recent innovations and newer releases like the TrailShot, the MSR MiniWorks remains one of the most popular pumps on the market. Compared to the Katadyn Hiker Pro above, both are similar in price (the Katadyn is $5 cheaper), both have the same filter pore size (.2 microns), and both protect against the same things including giardia and cryptosporidia. The Katadyn is lighter at 11 ounces, but the MSR has a significantly longer filter life at 2,000 liters (the MSR is carbon/ceramic while the Katadyn is carbon). And both allow you to filter water without the inconveniences of straws or droplets.

We have the MSR MiniWorks ranked here because of our personal experience with it. We found the pump to be slow from the outset (it has a listed flow rate of 1 liter per minute, but we didn’t experience that). More, our version became almost unworkable mid-way through a Utah backpacking trip. The water was rather murky, but that’s not excuse for pump failure just a few days out of the box. User reviews generally are positive and we are looking forward to getting another MiniWorks out this summer for more testing, but regardless, we’ll take the lower weight and initial cost of the Katadyn.
See the MSR MiniWorks EX


12. Sawyer Select S1 ($60)

Sawyer Select S1 water filterType: Straw filter
Weight: 10 oz.
Filter life: 946 liters
What we like: Fast flow rate.
What we don’t: Relatively heavy and better for travel than backpacking.

Sawyer keeps innovating in water filtration and purification, and the new Select series is case in point. This straw-style design includes a filter up top with a flexy silicon bottle below used to collect dirty water, all at a total of 10 ounces. This makes it heavier than ultralight options on this list like the Sawyer Squeeze and Katadyn BFree, the latter of which weighs only 2.3 ounces including a drinkable bottle. All have .01 micron filter pores, but the Select S1 does seem to have the fastest flow rate of the bunch. Sawyer also offers S2 and S3 versions of this system, with the latter being a full-on purifier that costs $30 more.

For backpacking, we have mixed feelings about Sawyer’s Select line. It’s a very nice concept, and particularly for travelers who aren’t necessarily counting ounces. For someone on the road and staying in hotels where they don’t want to drink the water straight out of the tap, it very well could be a top choice. However, the Select weighs 10 ounces, many times more than the all-in-one Katadyn BeFree, and it’s made to pour into a separate container. The Select S3 is more impressive as it purifies, but again, we think of this system as being more for travel than the backcountry.
See the Sawyer Select S1


13. Potable Aqua Tablets ($10 for a package of 50)

Potable Aqua TabletsType: Chemical purifier (tablets)
Weight: 6 oz.
Shelf life: 4 years
What we like: Lightweight and cheap.
What we don’t like: Tastes funky and takes 30 minutes to activate.

Potable Aqua tabs are a classic and something that we’ve used as a filter backup for years. The system couldn’t be simpler: put two iodine tablets in a liter of water, wait 30 minutes, and drink. Most importantly, they kill bacteria, protozoa, and viruses, thereby purifying water for drinking. Similar to the Aquamira Drops and SteriPen above, keep in mind that you will be drinking unfiltered water, so Portable Aqua is best used in relatively clean mountain water. 

The big downside of Potable Aqua is taste. Neutralizer tablets are included and do a decent job at masking things, and many people add a drink mix to make a concoction that tastes less chemical-like. In comparing chemical purifiers, we prefer the Aquamira droplets above, which are lighter (3 ounces vs. 6 ounces for the Potable Aqua with neutralizing tablets), and work in 20 total minutes instead of 30. If you’re wondering about the differences between iodine (Potable Aqua) and chlorine dioxide (Aquamira), the former is not effective in killing cryptosporidium, while the latter is categorized by the CDC as having low to moderate effectiveness.
See the Potable Aqua Tablets


14. Sawyer Mini Filter ($25)

Sawyer Mini FilterType: Straw filter (gravity adapter is available)
Weight: 2 oz.
Filter life: 100,000 gallons
What we like: Feathery light.
What we don’t like: We’ll stick with the better performing and longer lasting Sawyer Squeeze.

One ounce lighter and $15 cheaper than the Sawyer Squeeze above, the Sawyer Mini is one of the lightest and most compact water filters on the market. Like the Squeeze, the Mini attaches to its included bag or other compatible water bottle to squeeze filtered water into your mouth or drinking vessel. Unlike the Squeeze, however, the Mini doubles as a straw, giving it the versatility of a bottle, straw, or gravity filter (the gravity option requires purchasing extra components).

It shouldn’t come as a surprise that this smaller and less expensive version is slower to filter and more prone to clogging. Additionally, the Mini is lighter on accessories: the 16-ounce pouch isn’t as useful for filling up standard water bottles, and you have to pay extra for attaching it to a hydration reservoir or converting the Mini into a gravity system. Taken together, we think the Squeeze is worth the extra 1 ounce and 15 bucks. But if you’re looking for the absolute lightest filter out there, the Sawyer Mini ties the Lifestraw for that distinction and functions well as an emergency backup.
See the Sawyer Mini Filter


15. Katadyn Base Camp Pro 10L ($100)

Katadyn Base Camp Pro 10LType: Gravity filter
Weight: 13 oz.
Filter life: 1,500 liters
What we like: Huge capacity makes it great for big groups and basecamping.
What we don’t like: Filter clogs easily with no way to backflush.

The Katadyn Base Camp Pro stands out on this list as the largest capacity gravity filter, and it’s great for large groups, basecamping, and families. Impressively, it can hold 10 liters at a time and even doubles as a backcountry shower with an adapter (sold separately). The Base Camp works similarly to MSR’s AutoFlow above: it’s a one-bag design with an on/off valve and hose that fills anything from water bottles to reservoirs and cook pots.

We don’t recommend using the Katadyn Base Camp Pro for anything other than clear water, however—the system is made without the ability to backflush to remove buildup on the filter. Although Katadyn recommends swishing a liter of clean water in the reservoir, there is essentially no great method for removing debris once the filter is clogged. The flow rate will slow down significantly at this point, rendering the system tough to use. When attempting to filter unclear water, Katadyn recommends filling other containers with water, letting the sediment settle, and then adding the water to the Base Camp Pro. We think this is a rather arduous and archaic process, and prefer to stick with the Platypus GravityWorks or MSR AutoFlow instead.
See the Katadyn Base Camp Pro 10L


16. Grayl Ultralight Water Purifier Bottle ($60)

Grayl Ultralight Water Purifier BottleType: Bottle purifier
Weight: 10.9 oz.
Filter life: 150 liters
What we like: An innovative and simple purification system.
What we don’t like: Not a versatile design (one bottle per person).

The Grayl Ultralight Water Purifier is a relatively new product designed with travel and light adventuring in mind. We like the concept: in their original Kickstarter video, the company parades an assortment of water filtration and purification systems, telling viewers they’ll no longer need these awkward devices that require squeezing, pumping, batteries, hoses, and even chemicals to work. Grayl then displays their product, a sleek 16-ounce bottle with a combo filter/purifier with a French press-style plunger.

Though catchy and certainly useful for a wide range of scenarios (think traveling in lesser-developed countries or hydrating in camp), the Grayl has limitations. Purifying just .5 liters at a time, this would be a rather inefficient system for anything but on-the-go drinking when water sources are consistently available. Additionally, the purifier cartridge has a lifespan of only 150 liters, lower than any other filter or purifier on this list. That said, we really like the Grayl for traveling abroad, and it’s a great replacement for buying water in disposable plastic bottles. For backpacking, the practicality is limited.
See the Grayl Ultralight Water Purifier Bottle


Water Filter and Purifier Comparison Table

Filter/Purifier Price Type Weight Life Flow Rate Capacities
Platypus GravityWorks 4L $120 Gravity filter 11.5 oz. 1,500 liters 1.75 liters/min 2L, 4L
MSR Guardian $350 Pump purifier 17.3 oz. 10,000 liters 2.5 liters/min Unlimited
Sawyer Squeeze $40 Straw/gravity filter 3 oz. 1 million gallons 1.7 liters/min 32 oz.
Katadyn Hiker Pro $85 Pump filter 11 oz. 750 liters 1 liter/min Unlimited
Aquamira Drops $15 Chemical purifier 3 oz. 4 years 1 liter/15 min 30 gal.
Katadyn BeFree Bottle 1L $45 Straw filter 2.3 oz. 1,000 liters 2 liters/min 20 oz, 1L, 3L
MSR AutoFlow 2L $110 Gravity filter 10 oz. 1,500 liters 1.75 liters/min 2L, 4L
SteriPen Adventurer Opti $90 UV purifier 3.8 oz. 8,000 liters 1 liter/90 sec N/A
MSR TrailShot $50 Pump filter 5 oz. 2,000 liters 1 liter/min Unlimited
LifeStraw Water Filter $20 Straw filter 2 oz. 4,000 liters Unavailable Unlimited
MSR MiniWorks EX $90 Pump filter 16 oz. 2,000 liters 1 liter/min Unlimited
Sawyer Select S1 $60 Straw filter 10 oz. 946 liters 20 oz./10 sec 20 oz.
Potable Aqua Tablets $10 Chemical purifier 6 oz. 4 years 1 liter/30 min 25 qt.
Sawyer Mini Filter $25 Straw filter 2 oz. 100,000 gallons Unavailable 16 oz.
Katadyn Base Camp Pro $100 Gravity filter 13 oz. 1,500 liters 2 liters/min 10L
Grayl Ultralight Bottle $60 Bottle purifier 10.9 oz. 150 liters .5 liter/15 sec 16 oz.


Water Filter and Purifier Buying Advice

Water Filtration vs. Purification

These two terms are often used interchangeably, but water filters and purifiers are not, in fact, the same thing. Simply put, the difference between a water filter and a water purifier is in the level of protection against microorganisms that they provide. In general, filters protect against protozoa and bacteria, while purifiers add viruses to that mix.
Katadyn Hiker Pro water filter (filling up)

Water Filters
Water filters take the form of cartridges with tiny microscopic pores that physically strain out harmful elements. Microorganisms that are large enough to be stopped by filters include protozoa (such as the notorious Giardia) and bacteria (such as E. Coli and Salmonella). Water filters do not, however, protect against viruses (Hepatitis A and the Norovirus, for example). The current consensus is that filtering your water should be sufficient for use in the North American backcountry including the United States and Canada. Viruses, which are transported primarily by human waste and occasionally animal waste, are rarely found in glacier melt or moving streams. But as we will say a number of times in this article, virus protection certainly isn’t a bad thing, even in North America. It’s better to be safe than sorry.

Water Purifiers
Like water filters, purifiers remove protozoa and bacteria from water, but they also combat viruses too small for most filters. This takes place either through the use of chemicals, ultraviolet light, or tiny fibers such as those used in the MSR Guardian. Purifiers are essential to obtaining drinking water in less-developed regions of the world where water sanitation and infrastructure aren’t as robust and viruses may find their way into the water. Most water purifiers do not filter sediment or other particles from the water, so in some cases the combination of a water filter and a water purifier might be necessary. The pricey MSR Guardian is the exception here—it functions as a pump filter, yet water runs through fibers so microscopic that viruses are kept from passing as well.
MSR Guardian (water close-up)

Types of Water Filters and Purifiers

Gravity Filters
Gravity filters are the fastest and easiest way to get clean water in the backcountry, provided you have a decent source from which to collect. You simply connect the parts, fill up your dirty water bag, hang it from a tree branch or rock, and let gravity do the work. Instead of pumping, water flows downward through the filter and into a separate reservoir for drinking. Gravity filters are awesome (our top overall pick in this article is the Platypus GravityWorks) as they treat large amounts of water without the arduous task of pumping, then dispense it easily. Because of the volume of water they can treat, gravity filters are a great choice for backpacking in groups and basecamping.

There are a couple of downsides of gravity filters. First, the parts can be somewhat bulky as the system includes as least one bag (dirty water) and often two (the clean water bag technically is optional as you can filter directly into bottles), the hoses, and the filtration unit. If you’re looking for the smallest and lightest setup for backpacking, a number of minimalist straw filters, hand pumps, and chemical treatments can achieve those goals (see the Sawyer Squeeze, to start). And using a gravity filter does require scooping water into the dirty bag, which is best done from at least a moderately sized stream or pond. You’ll also need a place to hang the clean water bag to let the filter do its work, unless you want to hold it at head level as the water filters downward. 
Platypus GravityWorks filter (in use)

Pump Filters/Purifiers
When you hear the term “water filter,” a pump probably comes to mind. Pump filters have long dominated the world of backcountry water filtration, only recently being overshadowed by new technology like gravity and bottle filters. A pump filter uses the action of—you guessed it—pumping to siphon water from the source, through a hose, into a microscopic filter, and out another hose into a clean receptacle. Pump filters, unlike gravity filters, are great for using on the trail to filter a liter or two while hiking, and adept at pulling water from shallow sources (we depend on them in Utah where it’s often difficult to scoop large quantities). However, filtering water with a pump can be arduous, field maintenance often is required to clean the cartridges, and pump filters are among the heaviest water filtration systems. Two of the leading pump filters in 2018 are the Katadyn Hiker Pro and MSR MiniWorks, and the MSR Guardian is in a class of its own as a pump purifier.
Katadyn Hiker Pro (close-up)

Straw Filters
Used commonly by day hikers, trail runners, and mountain bikers who prefer not to carry water as they move, straw filters allow you to drink directly from the source. They often use the pressure of sucking to transport water from a stream, lake, or bottle, through the filter and into your mouth. On average, straw filters are lighter and cost less than pump or gravity filters, but they are functional in limited environments, such as when water is readily available and no storage of water (for cooking or drinking later, for example) is needed. One of the most well known straw filters is the basic LifeStraw.

It’s worth noting that a couple of prominent straw filters do require some squeezing action. The Sawyer Squeeze, for example, isn’t a traditional straw filter because you have to hold the dirty water bag up and squeeze to create the flow—much like you would with a tube of toothpaste. And the Katadyn BeFree essentially is a lightweight straw filter with a silicone water bottle included for direct drinking.

Chemical Purifiers
We hesitate to call them old school, but chemical purifiers have been around forever yet still get the job done. The most well known chemical system is Potable Aqua iodine tablets, which you simply add to water and wait 30 minutes before drinking. The upsides are clear: tablets are lightweight and cheap, not to mention you get decent virus protection too. But keep in mind that tablets and similar chemical options like Aquamira chorine dioxide drops go straight into unfiltered water. This means that whatever amount of silt, twigs, and critters are in that water will be in your bottle too. For this reason, tablets and drops work best when you have easy access to good water sources like glacial streams. A final note on chemical purifiers: taste often can be an issue, especially with iodine. Potable Aqua does come with neutralizer tablets, but it’s hard to avoid that chemical taste.
Ultralight water filtration

UV Purifiers
One purification system on this list, the SteriPen Adventurer Opti, uses unique UV purification methods. In terms of process, you place the SteriPen in your water and swirl for about 90 seconds until the light turns green (it may take more time if the water is very cloudy or cold). Similar to the chemical purifiers listed above, the SteriPen goes directly into unfiltered water and therefore you’ll want a good source. Another downside of UV purification is that it requires batteries and electronics to work, which can go dead or otherwise fail in the backcountry. For this reason, we recommend bringing backup batteries and/or filtration options such as drops or tablets (in fact, this always is a good idea no matter your system).

Bottle Purifiers
In addition to new bottle filtration options like the Katadyn BeFree, there is a bottle purification system on the market: the Grayl Ultralight. This all-in-one system works well for day hikers and other on-the-go adventure seekers, making it possible to grab water from the source and drink it immediately. Bottle purifiers usually are lighter than pump and gravity filters, although they still can’t compete with true ultralight options (the Grayl Ultralight weighs 10.9 ounces total, for example). However, the water quantity you can purify still is fairly limited—0.5 liters for the current Grayl model—and the cartridge lifespan is short at only 150 liters. We like the technology, and particularly for day hikers and travelers who aren’t counting ounces, but weight and volume considerations make it less attractive for serious backpacking.

Weight and Bulk

As with all backpacking gear, the goal is to go as light and small as possible. The good news is that with water filtration and purification, now more than ever there are a number of super lightweight and packable options. It all starts with chemical droplets and tablets, which are around 3 ounces total (or 6 ounces for iodine if you bring the taste neutralizing tablets) and take up almost no space in your backpacking pack. There also are ultralight straw filters like the LifeStraw and Katadyn BeFree, which weigh in the 2 to 3-ounce range but are slightly larger in size than chemical treatments. Pumps and gravity systems take up the most space and are the heaviest, ranging from around 11 ounces for the Katadyn Hiker Pro to 17 ounces for the MSR Guardian. These systems also have multiple components including storage bags and hoses, but work great for groups and basecamping.
LifeStraw water filter in use

Filter Life

A key product specification that we reference in this article is filter life, or how quickly your filter will need to be replaced. The primary consideration here is cost: you have the initial purchase price of the device, but after a certain number of liters of water have been filtered, you’ll need to buy a replacement cartridge. For example, two of our favorite pump filters are the Katadyn Hiker Pro and MSR MiniWorks. The purchase price of the Katadyn is $5 less than the MSR, but it has a shorter filter life of 750 liters vs. 2,000 liters. Given that the Katadyn replacement filter costs $50 vs. $40 for the MSR, this brings the cost of the system up over a period of years. On the extreme ends of the spectrum, the Grayl Ultralight purifying bottle has a cartridge life of only 150 liters, while the Sawyer Squeeze has a 1-million-gallon guarantee and they don’t even make replacement cartridges for it.

As with any manufacturer-provided spec, the listed filter life is optimistic and probably should be thought of as a maximum. More, many of these filters and purifiers are made with lots of plastic and it’s fairly likely that you’ll break another component of the device before the filter expires. Finally, the 750 liters referenced above for the Katadyn is a lot for most casual backpackers that get out a few times a year. If your filter lasts that long and you’re ready for a new cartridge, then you’ve gotten a lot of use and clean water out of it, making it a solid investment.

Flow Rate

In practice, you’re most likely to drink adequate amounts of water in the backcountry if it’s quick and easy to obtain. Thus, flow rate, or the speed of your filter, matters. Gravity filters generally have the fastest flow rates­—both the Platypus GravityWorks and MSR AutoFlow are 1.75 liters per minute, which means it only takes a few minutes to fill a 4-liter bladder with clean water. The leading pump filters on the market are listed at about 1 liter per minute, although that seems fairly optimistic to us. The exception is the pricey MSR Guardian, which is listed at a speedy 2.5 liters per minute. Although not technically flow rate, chemical purifiers take between 20 and 30 minutes depending on the product of your choosing. Again, the flow rates listed by the manufacturers are going to be realized in optimal circumstances and are likely to be slower in the field. Most filters come with recommendations for backflushing or light maintenance to keep things moving properly (more on that below).
Pumping water (MSR MiniWorks)

Pore Size

If you’re getting deep into water filter/purifier research, you may come across the term “pore size,” which is measured in micron. This refers to the size of the tiny openings in the filter, and the smaller they are, the more particles the filter can block. According to the CDC guide on water treatment, microfiltration units range in pore size from approximately 0.05 micron to 5 micron. Many backpacking filters on this list have a pore size of .1 or .2 micron, which is effective against protozoa (Cryptosporidium, Giardia) and bacteria (Salmonella, E. coli, etc.), but not viruses (Hepatitis A, Norovirus, etc.). The MSR Guardian is unique in terms of being a pump purifier due to the medical-grade fibers used in the filter.

Compatibility with Water Bottles and Hydration Reservoirs

Almost all water treatment systems have some way of connecting to either a water bottle or hydration reservoir, if not both. This often takes the form of a simple hose or cap that fits onto commonly-sized water bottle openings. The MSR AutoFlow, for example, has a tube that can connect with MSR reservoirs for a streamlined gravity system, and pump filters like the Katadyn Hiker Pro and the MSR MiniWorks have adapters that fit the mouth of a standard Nalgene bottle. Sawyer has played into the fast-and-light community of hikers who use disposable plastic water bottles on the trail, making their Squeeze and Mini versions able to screw into the mouth of a standard plastic water bottle (great for weight savings, less great for the environment). All in all, be mindful of the compatibility for a water filter or purifier to make sure it works with your drinking vessels.
Katadyn Hiker to water bottle

Water Taste

If you’re picky about the taste of your water, you’ll want to listen up here. Many water filters and purifiers are able to remove bacteria, protozoa, and sometimes even viruses, but they won’t necessarily change the taste of the water. This isn’t a huge issue when you’re drinking straight from cold mountain streams, but it definitely can be as the quality of your water source deteriorates. If you’re using chemicals to purify your water or drinking from questionable sources—perhaps water with floating leaves or plants growing underneath the surface—taste can come into play in a big way. If the bad taste really bothers you, we recommend adding an electrolyte-enhanced drink mix, or in the case of Potable Aqua, using the accompanying neutralizing tablets.

In addition, carbon filters are known for helping with taste. Used in the popular Brita kitchen filters, carbon removes chlorine, organic compounds, and other bad odor and taste-inducing materials. Not all portable backcountry filters use carbon, but many on our list do including the Katadyn Hiker Pro, MSR MiniWorks, and Grayl Ultralight Purifier. Additionally, some models offer carbon filters as add-ons: the Platypus GravityWorks, for example, sells a carbon element separately that can be added to the existing filter, and the LifeStraw Steel edition uses carbon instead of a hollow-fiber membrane. It’s important to note that carbon becomes ineffective before the filter (after approximately six months or 200 liters), so if this is a feature you want to maintain, choose a filter that allows you to purchase the carbon element separately from the complete cartridge.
Drinking water (Katadyn BeFree)

Filter Maintenance/Replacement

Given that their task is to remove contaminants from water, it should come as no surprise that many water filters need to be cleaned of this buildup. Most gravity and straw filters are maintained by backflushing clean water or air through the filter. With the Lifestraw, this is as easy as blowing out after each drink. With the MSR AutoFlow or Katadyn Basecamp Pro, however, it can be as complicated as finding a bladder with a compatible hose attachment to force water back through the filter. In general, it’s important to read about and practice maintaining your filter at home before taking it out into the field.

Cleaning pump filters is a slightly more intensive process, as it involves unscrewing the apparatus and either removing the filter or extending a brush down the interior. Instructional videos are available online for almost every product on our list, and you should expect basic maintenance to be part of owning and using a water filter. If you’re not keen on keeping up your equipment, you can always opt for more carefree models like the SteriPen or chemical treatments like Aquamira or Potable Aqua.
Scooping Water (Platypus GravityWorks)

Emergency Backups

Last but not least, we should mention that just about every water filter and purifier can malfunction, which may leave you without clean water in the backcountry. In this scenario, you can boil your drinking water provided you have a backpacking stove and extra fuel, but this a time and labor-intensive method. For this reason, we think it’s a good idea to carry a lightweight chemical treatment or LifeStraw as an emergency backup. The LifeStraw weighs just 2 ounces and costs $20, and Potable Aqua tablets are just $8 for 50 tablets. If you don’t bring the taste-neutralizing bottle as this is for emergency use, that’s just 3 extra ounces in your backpack. Getting sick in the backcountry can be a serious medical concern, so we think having a backup is a smart way to go.
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