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  • Steven Boldt

Water Treatment in the Backcountry

It's almost needless to say, but we're saying it anyway - hydration is critical when you're out on the trail! Carrying a bottle or bladder is the easiest way to make sure you're drinking enough water, and when you're just about dry, it's time to refill. If you're in the backcountry or there isn't a drinking fountain or sink nearby, you'll have to head to a natural source. But then you'll also have to ask yourself, is there something in the water?

To call a spade a spade, anywhere humans or animals are active means the water could be contaminated. And without microscopic testing, it's impossible to know for sure. Treating water to remove any potential disease causing pathogens is incredibly important - ingesting a 'bug' could ruin your backpacking trip with painful stomach aches and diarrhea, or even land you in a hospital.

Purifiers vs. Filters

When looking at water treatment products on the market, you'll notice 'purifier' and 'filter' are commonly used in product names or descriptions - they describe the organisms the product treats for. Purifiers remove all pathogens, including viruses; filters only remove larger pathogens (protozoa and bacteria) and not viruses, which are much, much smaller.

So why use a filter if it doesn't remove viruses?

Fortunately, in the US & Canadian backcountries, a filter is generally considered to be enough protection. As these areas are pristine, the main worry is ingesting protozoa or bacteria from animal sources. Viruses are species specific, so humans get viruses when other human fecal matter gets into the water supply; where there are no other humans, there's a minimal risk of encountering a virus.

When should I use a purifier?

Purifiers can provide peace of mind if you're noticing people at popular outdoor spaces aren't using proper waste disposal techniques, or worse, none at all. As a rule of thumb: more people in an area means more viruses in the water, and the more likely it is that you should use a purifier. They are also commonly used when traveling abroad in places with poor or questionable water treatment and sanitation facilities.

What kind of purifier technology is out there?

For the longest time, purification was just achievable though boiling or adding chemicals, more recently UV light purifiers have been developed to neutralize pathogens. And within the last few years, physical purifiers have hit the market - they utilize revolutionary cartridges to physically remove pathogens, including viruses.

Cartridges & Elements

Every filter and most physical purifiers use porous cartridges or elements that trap pathogens and other debris, but allow water molecules to flow freely through them. Cartridges are made from strands of hollow fiber, elements are made of ceramic or carbon.

A water filter cartridge from Platypus GravityWorks 4L water treatment system showing the direction of flow by arrow.
A cartridge from Platypus, note the Flow arrow!

Without getting too nerdy, filters (can be either elements or cartridges) have openings no larger than 0.2 microns, so they are able to trap larger pathogens, but not viruses. Physical purifiers (only made from hollow fiber cartridges) have openings that are no larger than 0.02 microns, which is why they trap everything, including viruses.

Be gentle with them!

All elements and cartridges need to be handled carefully - dropping them can crack them internally, which would increase the pore size and allow pathogens to get through.

Freezing is another condition that can destroy them! As water freezes, it expands inside the cartridge or element, which like dropping, cracks them, increases the pore size, and renders them ineffective. If the filter has never been used or wetted, it's OK if it freezes. If it has been used and then freezes, it needs to be replaced; unfortunately, there's not any failsafe test that can be done at home to ensure its integrity.

If you have any concern at all that your cartridge or element has been damaged, replace it!


As a cartridge or element gets used, debris builds up inside it, bringing the outflow of water to a trickle, or nothing at all. Backflushing is a method of cleaning the cartridge/element by reversing the treatment process. CLEAN WATER is routed to flow from the dirty side of the cartridge/element, out the clean side. This clears any particles or pathogens that were trapped inside and leaves a renewed cartridge/element.

All systems that require it have a different method of backflushing. Follow the manufacturer's suggested methods to ensure success and avoid cross contamination.


Methods & Products

The four main methods to treat water for pathogens:

  • Physically removing pathogens by running water through an element or cartridge

  • Ultraviolet (UV) light treatments that disrupt the DNA of pathogens, killing them

  • Chemicals that are added to the water to break the pathogens apart atomically

  • Boiling the water to kill pathogens with heat

There are an incredible amount of water treatment products and systems.

When looking at water treatment products, it's good to remember that they have been designed an manufactured for different uses and situations. What works for you in one setting, might not work in another. Below we'll describe different product classes on the market, where they excel and where they fall behind, and we'll also link a few of our favorites in each class.

If you're new to water treatment systems, we suggest starting with the product(s) that will initially suit your needs for the highest proportion of your adventures. Then, based on your experiences with your first system, you can continue building out your gear closet with new products suited to your evolving needs and wants.

Pump Filters & Purifiers

Pump filters have been around for quite some time and utilize a mechanical pump to pull water up a dirty water hose and force it through a filter. The now protozoa and bacteria free water flows out of a clean hose into your bottle or cook pot.

Pump purifiers, like the MSR Guardian Purifier, have been developed with an incredibly fine cartridge that also removes viruses. The process is the same, and MSR even claims that the system cleans (backflushes) its own cartridge which saves on chores. The downside? A very high cost and 1lb. weight.

Person by a mountain creek, using an MSR Water Pump to treat water.
Using a mechanical pump filter. Note the flowing water - more movement, less pathogens!

Where Pumps Excel

  • Pull water from very shallow/seeping water sources

  • Process the exact amount of water you need, including large amounts, relatively quickly

  • Some pumps have a built-in prefilter, making them great for cloudy or sedimented water

Where Pumps Fall Behind

  • The actual pumping, along with the field cleaning most models require, are more work than other options

  • They are heavy and bulky

  • For pumps without a prefilter, cartridges can become clogged and stop functioning when water is cloudy or sedimented so another method of prefiltering will be necessary (see our Prefiltering section below for different techniques)

  • Cartridge/element can crack in freezing temperatures or if dropped, rendering treatment ineffective

Our Favorite Pump Products

Flow Rate 1L/min 2.5L/min

Product Weight 11 ounces 18 ounces

Cartridge Life 750L 10,000L+

Initial Cost $70 $350

Replacement Cartridge Cost $50 $180


Gravity Filters & Purifiers

Gravity systems usually come with two bladders (one dirty, one clean), tubing, and an inline cartridge. They use the weight of the water and gravity to force dirty water through the cartridge:

  1. Fill the inclued dirty water bladder from a water source

  2. Hang the dirty bladder a few feet off the ground

  3. Connect the tubing and inline cartridge to the clean water bladder (in the right direction!); then connect to the dirty water bladder

  4. Let gravity do its work


With the tubing still attached, simply hold the clean bladder higher than the dirty bladder. Let a few ounces of clean water flow back through the cartridge, which removes the debris. Disconnect the tubing and empty the dirty bladder of the water/debris.

Where Gravity Systems Excel

  • Super convenient and intuitive

  • Great for large groups and treating a lot of water

  • Easy to backflush and clean

  • Minimal work, just fill the dirty bag and let gravity do its work

Where Gravity Systems are in the Middle

  • Weight - they're not super light, but not super heavy

Where Gravity Systems Fall Behind

  • Can be painstaking to fill the dirty water bag from trickling or shallow water sources

  • Silty or murky water can clog the cartridge, with those conditions, prefiltering will be necessary (see our Prefiltering section below for different techniques)

  • Cartridge/element can crack in freezing temperatures or if dropped, rendering treatment ineffective

  • Bulky

Our Favorite Gravity Products

(comes in 2/4/6L versions) Gravity Purifier

Flow Rate 1.5L/min 0.5L/min

Product Weight 10-12 ounces 20 ounces

Cartridge Life 1,500L 3,000L

Initial Cost $100-120 $250

Replacement Cartridge Cost $55 $190


Other Cartridge Products

These are some other water treatment products that we believe are worth a mention. Aside from one purifier product, they all utilize a filtration cartridge to treat water and they are all best used by one or two people - perfect for going deep in the backcountry on ultralight missions.

A straw with an internal filter. Just put the dirty end in the water source and drink directly. It’s lightweight and great for an emergency backup solution or for day trips. It’s not practical for large amounts of water, and requires lying on your stomach next to the water source. That said, the filter will last for 4,000L and for just $20, there's really no reason not to own one.

Lifestraw Specs

Flow Rate - N/A | Weight - 1.6 ounces | Cartridge Life - 4,000L

Cost - $20 | Replacement Cartridge Cost - N/A


Sawyer MINI Water Filter These filters are incredibly versatile! They are often used ‘in-line’ with a hydration bladder - fill the bladder with dirty water, as you suck water out, it passes through the filter and you get clean water! They can also be screwed directly onto standard size disposable water bottles and drank from directly.

Sawyer MINI Specs

Flow Rate - 0.6L/min | Weight - 2 ounces | Cartridge Life - 380,000L (you read it right!)

Cost - $22 | Replacement Cartridge Cost - N/A


MSR Trail Shot The Trailshot is an interesting product - a small hose, with a prefilter attached, goes into the water source. On the other end of the hose is a hand pump, filter, and spout. Use the pump to draw water up through the filter and out the spout. It’s incredibly compact and great for shallow/trickling sources! Though after filtering a lot of water, the hand pump will get tiresome.

MSR Trail Shot Specs

Flow Rate - 60 pumps/L | Weight - 5 ounces | Cartridge Life - 2,000L

Cost - $50 | Replacement Cartridge Cost - $35


The BeFree is what’s known as a squeeze filter. Fill the included dirty water bag, attach the filter, and squeeze the bag. The water is forced through the filter and goes directly into a clean bottle, or your mouth! These systems, while convenient, can lack durability from squeezing the bag repeatedly. Also the filter isn’t able to be backflushed super well so it’s important to use clear water. These systems are very popular right now - also check out the Sawyer Squeeze and the Platypus Quickdraw Microfilter System.

Katadyn BeFree 1L Specs

Flow Rate - 2L/min | Weight - 2.2 ounces | Cartridge Life - 1,000L

Cost - $45 | Replacement Cartridge Cost - $25


GRAYL Water Purifier Bottle GRAYL has developed a personal size bottle that purifies water through a proprietary cartridge. The bottle pulls apart into an outer shell and an inner purifier. Fill the outer shell with dirty water and push the inner purifier down into the bottle, as the water flows through it’s cleaned.

GRAYL Water Purifier Bottle Specs

Flow Rate - 5L/min | Weight - 16 ounces | Cartridge Life - 350L

Cost - $90 | Replacement Cartridge Cost - N/A


Ultraviolet (UV) Light Purification Devices

These are thick, pen-like devices with a UV light on one end and usually a display on the other. As the UV light hits pathogens, including viruses, it disrupts their DNA, effectively killing them.

To use it, put the waterproof UV light into your bottle and agitate the water in the bottle. Continue moving the water around for the specified time (usually 45-90 seconds depending on the amount of water) or until the display tells you you’re done.

Where UV Excels

  • No treatment issues in freezing temperatures (ie. no cracked cartridges.. that said, the batteries could be less effective in the cold, so keep the device in an internal pocket)

  • Device is lightweight

  • Treatment is convenient and fast

  • Neutralizes all pathogens, including viruses

Where UV Falls Behind

  • Dirty/silty/muddy water will impede the UV's effectiveness - prefiltering these types of water will be necessary (see our Prefiltering section below for different techniques)

  • Not efficient for large quantities of water

  • Battery powered, so batteries could fail (carry extra with you!

Our Favorite UV Product

Flow Rate 1L in 90 seconds

Product Weight 5 ounces

Cartridge Life 50L per battery charge

Initial Cost $120

Replacement Cartridge Cost N/A

More Information How It Works Video


Chemical Purification

Chemical purifiers generally come in either tablet (MicroPur) or liquid form (Aquamira). Simply place the purifier into your dirty water, let the chemicals do their thing for the suggested amount of time, and enjoy your purified water.

Most modern versions on the market utilize chlorine dioxide, a chemical sanitizing agent that disrupts cell membranes and protein production, effectively killing or neutralizing any pathogens in the water. It has been commonly used in municipal water treatment systems for years.

Where Chemicals Excel

  • Low Cost

  • Ultralight and take up essentially no volume

  • Easy to use

  • Great backup if other treatment options fail

Where Chemicals Fall Behind

  • Doesn't necessarily taste great

  • Wait time is long;

    • Usually 30-40 minutes to kill most pathogens; 4 hours are needed to kill Cryptosporidium)

    • Times are even longer if the water’s mucky; or if you prefilter and include that time.

  • Not all chemical versions will kill protozoa like cryptosporidium (make sure you check!)



The age-old technique of boiling! According to the WHO all you need is a few seconds above 158 ℉ to reduce 99.9% of all pathogens in your water, this includes viruses. Therefore, bringing the water to a rolling boil (212℉) for a minute or two will certainly kill everything (this is what the CDC recommends).

As water boils at a lower temperature at higher elevations, the CDC recommends boiling for 3 minutes if you’re above 6,500 ft. - the longer time is precautionary to make sure all of the contaminants are killed off.

Boiling any longer than the CDC recommended times is overkill, and more importantly if you’re in the backcountry and using stove fuel, a waste.

Where Boiling Excels

  • No question if it's effective - it always works to treat water

  • It's an easy process

Where Boiling Falls Behind

  • Requires a stove, pot, and fuel

  • If treating for drinking water, you now have hot water, which isn't always pleasant to drink


Gathering Water

Where To Gather

  • Flowing water, especially streams and rivers. The more the water flows, the less growth is possible and the less likely pathogens can survive.

  • If no flowing water is available, a still source is OK, just avoid spots with growth/floaties.

  • Clear sources - avoid heavily silted/sedimented areas.

  • Reach out into the body of water if possible - pathogens are more likely to be along the shore, in shallow water.

A great gathering spot - reaching out into clear, moving water.

Where To Avoid Gathering

  • Anywhere excrement could enter the water source, especially if the contamination source is upstream from you!

    • Sources near farms, meadows, or pastures where animals live and graze

    • Near popular or well established campgrounds

    • Sources near trails with pack animal or dog traffic

    • If you must gather from a source like this, use a purification method!

  • Sources with heavy silt, sand, or sedimentation that could clog filters

  • Sources with lots of foam, scum, or algae blooms - this is a rich place for pathogens

  • Dirty or discolored snow, especially if caused by human activity

  • Avoid gathering water directly after heavy rain (if possible). The rain will push ground surface materials (sand, soil, etc.) into the body of water, cloud it up, and increase the potential pathogen count.

The Colorado River: well known for it's silty, murky water. Prefiltering is a must!

How To Gather Water

  • When you’ve found a place, seek the clearest water possible, especially if filtering

  • Gather water from the surface - if you scoop down in, you’re more likely to accumulate silt, sediment, and mud

  • If you can’t avoid silt/sediment

    • Gather water in your cooking pot, let it settle for a few minutes, scoop out/carefully pour out the clear water on top to then filter

    • This is a super basic method of prefiltering that will only work for moderately murky water, for heavy silt/sedimentation please see the following section on prefiltering


Especially murky and heavily silted water should be prefiltered before treatment. Prefiltering will help remove the sediment and clarify the water, which is necessary to make certain treatment methods effective.

Using clear water is especially important when using UV treatments (the sediment blocks the light and the light is no longer guaranteed to hit all of the water, potentially leaving pathogens behind) and cartridge/element options (they can get clogged or dirty, rendering them useless).

Methods of Prefiltering

There isn’t one tried-and-true method of prefiltering - you’re going to have to do some trial and error to figure out what works best with the water you’re trying to clarify and your treatment system.

  • For a super low-tech, cost-effective solution, use a bandana, coffee filter, or pantyhose rubber banded tightly across the opening to your dirty water container. Pour from another ‘dirty’ bottle in your container or carefully dip your container into the source. It takes a bit more planning but Disposable nylon ‘try-on socks’ are perfect for this method.

  • Use one of these rubber washers with a fine filter (another version) on your dirty bottle.

  • This Steripen Prefilter Bottle Cap works wonders when using a Steripen or other UV treatment, but can also prefilter water before using another treatment method.

  • Micron Filter Bags, Millbank bags (another version) or Brown Filter Bags - not the most lightweight options, but work super well for large volumes!

  • Alum Powder (aka Aluminum Sulfate) is used to clarify and remove phosphorus in commercial systems, but works for backpacking too! The powder reacts with the particles in the water, creating a gelatinous ‘floc’ that can be easily removed or avoided, and leaves clear water. This method is particularly handy with really fine particles like silt. Alum powder is easily found in grocery store spice aisles or online. A general ratio is to add one teaspoon per liter of water, stir thoroughly, and let everything settle for 30-40 minutes before removing the floc and treating.

Leave No Trace Practices Near Water Sources

What happened to the days of old where you could stick your head into a mountain stream and take a big, refreshing gulp?? WE DID! It’s not the most enjoyable to talk about, but the reason we need to be more conscious of water treatment is because human and animal feces is making its way into our water supply.

Don't contaminate water sources - dispose your waste properly!

We strongly advise hikers to Dispose of (Human) Waste Properly. This could be as simple as using a backcountry composting toilet installed by the Forest Service or properly digging a cathole at least 200 ft. from water sources and 6-8” down (please see this Leave No Trace video on catholes).

Though the least likely to contaminate water sources, and the most sustainable method, is to use Blue/W.A.G. Bags and carry your solid waste out with you (check out this Leave No Trace video on using W.A.G. bags).

Other Leave No Trace Tips

  • Camp at least 200 ft. from water sources.

  • Dispose of any soapy water on soil - not in waterways or rocks where it could reach waterways.

    • Organisms in the soil will actually eat and metabolize any phosphates or microorganisms.

    • Soap usually contains phosphates, which can proliferate algae blooms and make waterways more favorable for pathogens.

  • Brush your teeth at least 200 ft. from water sources and make sure to spit/rinse on soil and not into waterways!

Closing General Tips

  • WASH YOUR HANDS, and your pots and pans!!

    • A lot of hiker’s who get sick, don’t actually get sick from bad water, it’s because of bad hygiene - hand-to-mouth contamination or contaminated pots and pans. (See this study from the Wilderness & Environmental Medicine Journal.)

  • If you don’t like the taste of your water:

    • Get an activated carbon filter! Some treatment methods include these or offer them as add ons. While they don’t make the water safer, they do make it taste better.

    • For a low tech, low cost solution - pour treated water between two containers a bunch of times. The added air should improve the taste.

  • If you’re not sure about the source and don’t have a purifier - use both a filter and chlorine tabs, when it comes to water, it’s always better safe than sorry!

  • Bring a backup treatment method! Sticking some chemical purification tabs in your first aid kit is simple and essentially adds no weight to your pack.




Steven, the author, lives in Portland, OR and is the Head of Wilderness Data and Community for RightOnTrek. When he’s not hiking, biking, or snowboarding in the Cascades, you can catch him eating a sushi burrito and drinking a beer at one of Portland’s food truck pods.


Have any water treatment tips or products you think we should cover? Let us know in the comments or email



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