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    How to Choose a Backpacking Water Filter or Purifier

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    When backpacking, never set out without a hydration plan. While you should always bring water with you, sometimes it’s not possible to carry enough for the entire trip, especially if you’re exploring the wilderness for more than a day. That’s why you need a water filter or purifier. Even clear, idyllic streams can be contaminated with invisible pathogens that could make you sick. Don’t take a chance — always filter or purify water that you collect along your trek. The last thing you want to be doing is puking (or worse) in the middle of the backcountry. This guide will help you choose the best water treatment system so you stay hydrated and healthy in the outdoors.

    How water treatment systems work

    To understand which water treatment system you should invest in, first you need to understand how they work. There are three main types of pathogens that plague water:

    • Protozoa: Commonly cause cryptosporidiosis (a diarrheal disease) or giardia (a gastrointestinal illness).
    • Bacteria: Commonly cause Salmonella or E. coli infections, typhoid fever, and cholera.
    • Viruses: Commonly cause hepatitis or stomach flu.

    Water filters, also known as microfilters, physically remove protozoa, bacteria, and sediment from water. Filters are made up of several parts, including an element/cartridge that strains pathogens using microscopic pores. Viruses are too tiny to be strained by water filters. Water filters are typically sufficient in the back countries of the United States and Canada, where human activity is low and viruses aren’t much of a threat. Water purifiers neutralize protozoa, bacteria and viruses using UV light or chemicals (in most cases). Purifiers are recommended for backpackers in developing countries where water treatment and sanitation practices are suspect, or in places with high human activity. Though purifiers eliminate all three major pathogens, they will not strain out dirt or debris as microfilters do. If you’re collecting water from a source that contains sediment, but the threat of viruses is present, consider first filtering and then purifying the water.

    Types of water filters and purifiers

    There are several types of water filters and purifiers on the market. Your choice will depend on where in the world you’re going, the size of your group, and how light you want your pack to be (among other factors). Some backpackers prefer to have more than one filtration or purification method on hand. The following guide will describe the basics about each type of filter or purifier so you can select the best water treatment system for you.


    To use a pump filter, insert the end of a hose into the water source and pump water into your bottle or container. For convenience, some units can screw directly onto a wide-mouth bottle (such as a Nalgene). Pumps often feature a ceramic or glass-fiber filtration element with an activated carbon core, which helps improve the taste of water. Pros:

    • You can treat as little or as much water as you want.
    • Works with shallow water sources.
    • Removes debris and unpleasant tastes from water.


    • Pumping can be tiring after a long day of backpacking.
    • Heavier than most water treatment systems.
    • Regular cleaning of the element is required.

    Check out: The MSR MiniWorks EX is a tried-and-true filtration system that’s a good bang for your buck.


    With gravity filters, let nature do the filtration work for you. Gravity filters typically consist of two reservoirs, attached by a hose with a filter in the middle. By filling one of the reservoirs with dirty water and then hanging it higher than the clean water reservoir, the untreated water is forced through the filter into the clean bag. Pros:

    • Requires minimal effort.
    • Good for filtering large amounts of water.
    • Little extra weight if reservoirs are used in place of other water storage systems.


    • Need something on which to hang the system (such as a tree), or else you have to hold the dirty reservoir while filtering.
    • Difficult to fill the reservoir in shallow water.
    • Typically slower than pumping.
    • Requires regular backflushing of water/air to keep filter clean and working properly.

    Check out: The Platypus GravityWorks Water Filter System Kit contains a clearly marked “dirty” reservoir and multiple adapters to pump water directly into various containers.


    Sip water straight from the source through a straw-like filter. Alternately, you can fill a water bottle or container and drink through the cylindrical device from there. (Just make sure not to put filtered water in the same bottle unless you’ve sanitized the container.) Pros:

    • Easy to use.
    • Lightweight.
    • Typically cheaper than other filtration methods.


    • Can be difficult to get close enough to the water source to drink from it.
    • Not always practical because you can’t store filtered water.
    • Not ideal for groups or as sole filtration method.
    • Requires field cleaning.

    Check out: The LifeStraw Steel Water Filter weighs only 4.4 ounces and contains an activated carbon capsule that helps remove odors and bad tastes.


    For most bottle filters, all you need to do is fill a bottle and drink, since the filtration element is built into the straw or lid and treats the water while you sip it. Pros:

    • Easy to use.
    • Lightweight.
    • Typically cheaper than other filtration methods.


    • Not ideal for groups, since water quantity is limited by the capacity of the bottle.
    • Requires field cleaning.

    Check out: The Katadyn BeFree Collapsible Water Filter Bottle is easy to clean and weighs only 2.3 ounces. For protection against viruses, try the Grayl Ultralight Water Purifier Bottle.


    Squeeze filtration systems work much the same as bottle filters. Simply fill a water reservoir or pouch, screw on its companion filter, and squeeze the water into your mouth (or into a clean bottle) through the filter. Pros:

    • Easy to use.
    • Lightweight.
    • Typically cheaper than other filtration methods.


    • Not ideal for groups, since water quantity is limited by the capacity of the reservoir.
    • Requires field cleaning.

    Check out: Weighing only 3 ounces, the Sawyer Squeeze Water Filter System can be adapted to work with a variety of water bottles or inline hydration packs.


    These purifiers are small, handheld devices that use ultraviolet light to scramble the DNA of bacteria, protozoa and viruses, rendering them harmless. Simply insert the tip of the pen into the water and stir for about a minute. Pros:

    • Lightweight and compact.
    • Does not require cleaning.


    • Requires batteries or recharging.
    • Silty or debris-filled water must be pre-filtered because sediment decreases the effectiveness of the UV light.
    • Works best with smaller batches of water.

    Check out: The SteriPen Ultra features a rechargeable battery and a low-power indicator.


    Purify water in the backcountry by adding chemicals in the form of drops or pills and letting the mixture sit for a specified time before drinking it. Iodine, chlorine, and chlorine dioxide are common chemical purifiers. Pros:

    • Lightest and most compact option.
    • Inexpensive.
    • Can be used as an easy backup method in case your typical water filter/purifier fails.
    • Does not require cleaning.


    • Must monitor supply.
    • Takes anywhere from 30 minutes to 4 hours to effectively purify water, depending on the specific product.
    • Can leave an unpleasant taste in water.
    • Iodine does not kill the protozoan Cryptosporidium.

    Check out: A package of 30 Aquatabs purifies 60 liters of water and costs less than 10 dollars. Aquatabs are effective after 30 minutes.


    Ah, good old-fashioned boiling. This method eliminates all three major pathogens if you have time to spare and an extra fuel canister. Bring water to a rolling boil for one minute if you’re below 2,000 meters (6,562 feet) in elevation, and three minutes above 2,000 meters. Pros:

    • Highly effective, even with cloudy water.
    • Can be used as a backup method in case your typical water filter/purifier fails.


    • Requires extra fuel, which adds pack weight.
    • Boiling the water and then waiting for it to cool takes time.

    Check out: Any stove/pot/fuel combination will do. For a lightweight option, consider the MSR PocketRocket 2 backpacking stove with the GSI Outdoors Halulite Minimalist Cookset and an 8-ounce fuel canister.

    Tips for staying hydrated in the backcountry

    After you’ve chosen your water filter, follow these three basic tips so you can think less about water and more about having fun in the backcountry.

    • Never assume there will be water where you’re going. Research sources along your trek beforehand.

    Take note from Edward Abbey, an environmentalist author, who set out to a desert island off the coast of Mexico without a thorough plan for water. “We weren’t finding any [water],” Abbey wrote in Abbey’s Road. “One likely pothole after another, on inspection, turned out to be full of nothing but dry sand.”

    • Collect water from the clearest source you can, preferably a flowing body of water.
    • Thoroughly read the instruction manual for your water filter or purifier, and be sure to operate, clean, and store it properly. Some elements or cartridges need replacement after a certain number of uses, so be sure to stay aware of what your particular treatment system requires.

    Collecting, treating, and drinking water straight from the source instead of through a tap is a satisfying feeling. With the right water treatment system, you can drink freely without having to worry about getting sick.

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