Portable Water Filters and Water Purification
Systems For Backpacking and Traveling
Guidelines For Choosing a Portable Water Purifier or
Water Filter For Camping, Traveling, and Emergency Needs
Portable water filters and water purifiers ensure better access to clean drinking water.
Do you enjoy backpacking, carcamping or traveling to under-developed countries? Or perhaps you're concerned about being prepared in the
event of a natural disaster or emergency survival situation.
The vast assortment of water purification methods can be confusing to sort through.
These informative guidelines from an REI expert will help you choose a portable water purification system for your traveling and outdoor
needs or for your emergency survival kit.
The brief overview will help you clear up any confusion surrounding which type of water-treatment system is right for you.
- Remember the difference between a filter and a purifier. While both remove bacteria from water particles using a mechanical process of
pumping then forcing water through a filtering device, only purifiers can render viruses inactive using either an additional chemical or
- Waterborne viruses are believed to be less common in North American wilderness waters. But if you're traveling outside of the United States or
Canada, you may want to opt for the more involved, and hence perhaps more expensive, purifying system.
- When comparing portable water filters and purifiers, look for an absolute - not nomimal - pore size of 0.2 microns. This industry-wide
benchmark indicates the system's smallest filtering capability. No bacteria larger than 0.2 microns can get through. Though a larger pore size
of 0.3 or 0.4 may suffice in most situations, why take chances with your health?
- Depending on its function, a water-treatment system can have numerous parts, some of which will need to be maintained or replaced on a regular
basis. If your travel plans include many nights away from a reliable water source, you will not only have to pack the filter but the backup and
replacement parts that go with it.
- And finally, to get the cleanest water possible, be sure to clean and dry your portable water filter regularly. When in the outdoors, try to
collect still, clear water. Whenever possible, boil the water before treating it. Then let the first few streams of water pass before you
begin collecting your treated water.
The Murky Truth About Clear Water
Free-flowing mountain streams, for all their beauty and clarity, are not always the fountains of purity we imagine them to be. Backcountry water
sources - crystal-clear rivers, lakes and streams - sometimes harbor microscopic pathogens.
Giardia lamblia; Cryptosporidium; Campylobacter jejuni; Hepatitis A - All are members of an invisible fluvial zoo that may be present
in pristine-looking backcountry water.
- How do they get there? - When water becomes tainted by animal or human feces.
- What impact could such microbes have? - They can leave you reeling with diarrhea, abdominal cramps, nausea, weight loss and fatigue.
- How long might these symptoms last? - Between 4 and 6 weeks. Maybe longer.
More details on waterborne pests, and techniques you can use to defeat them, are explained in the REI Water Treatment clinic. In this
presentation the goal is to provide guidance on the water-treatment strategy
favored by most wilderness travelers - using portable water filters
Explaining Portable Water Filters and Purifiers
Portable water filters and purifiers both operate on the same mechanical principle. Using a hand pump and intake hose, both slurp up 'raw'
water from a lake or stream and force it through an internal element (a filtering 'medium'). This medium traps suspended elements - from fine
sediment to invisible microorganisms - before dispensing clean water into a container of your choice.
What's the Difference?
- Water filter - A microbiological device that removes bacteria (e.g., Campylobacter jejuni) and protozoan cysts (Giardia lamblia,
cryptosporidium) from contaminated water.
- Water purifier - A microbiological device that removes bacteria, protozoan cysts and viruses (e.g., hepatitis A) from
Viruses are infinitesimal organisms too tiny to be trapped by a filter. Devices identified as 'purifiers' usually cause water to interact with
iodine (often in the form of iodine resins), which can render viruses inactive. Another purifier uses a positive electrostatic charge in its
filter medium to capture viruses.
- may exist in water wherever there is a reasonable chance of human fecal contamination
- are believed to be less prevalent in North American wilderness water sources than protozoan cysts or bacteria, but may be a greater threat
in less developed countries.
Over time, portable water filters have proven that they reliably protect wilderness travelers from the most common waterborne pathogens found
in the North American backcountry: giardia and cryptosporidium. Still, purifiers and their antiviral feature offer an elevated level of security.
To fully disinfect suspect water using a water filter, the Centers for Disease Control and Prevention recommends:
- mechanically filtering the water
- treating it with a halogen (chlorine or an iodine solution)
- letting it sit 15 to 60 minutes
- then drinking it.
What Really Matters
In an ideal world, portable water filters or purifiers will be:
- Simple to use
- Easy to pump
- Capable of sustaining a steady, generous flow
- Effective against waterborne pathogens
- Slow to clog, easy to clean
How can you tell if a filter or purifier delivers in these areas? Look for clues in the specification chart that accompanies each product description.
Understanding Spec Charts
Here's how to interpret the information:
Filter medium - This is the cartridge that actually traps pathogens (plus silt and other debris). The composition of the medium
contributes greatly to the quality (and cost) of a device. Medium materials include:
- Ceramic: This is an effective, high-quality earthen material that can be cleaned many times before it needs a replacement. A
ceramic cartridge captures most particles within .005 of an inch of its surface, so it's easy to brush away clogged pores and expose new ones.
Cartridges themselves are fragile and require careful handling. Ceramic elements are the longest-lasting mediums and make a good choice for
frequent backcountry visitors.
- Ceramic with a carbon core: This additional layer helps filter out the taste of halogens (chlorine and iodine) plus some organic
chemicals, herbicides and pesticides.
- Fiberglass (or glass fiber): As effective as ceramic in straining out pathogens, but not as long-lasting.
- Structured matrix, or labyrinth: A dense, honeycombed material that effectively captures pathogens.
- Iodine resin: A chemical layer integrated with a purifier's filtering medium that deactivates viruses, though it does not
actually remove them.
Field cleanable - A desirable feature. This means you may open the filter to brush or scrub the filter medium and increase water flow.
Clogging should not cause you alarm; it shows the filter or purifier is working. Ceramic filter media can usually accept dozens of cleanings. Some
models can be cleaned through backwashing (feeding clean water through the filter in reverse) but you need ample clean water in order to do so.
Longevity - How long will a filter or purifier last? Ceramic filters that can accept cleaning will last the longest, but the life of any
filter depends on the clarity of water you pump through it. If possible, seek out clear water in still pools. You're likely to find
less sediment in such water than in rushing water. Use a pre-filter if your device includes one. Manufacturers sometimes include an
estimate of the number of liters a filter or purifier is expected to treat effectively.
Pump force - The higher the number, the harder it is to pump. The Katadyn Pocket Filter, for example, has a pump force number of 16.5.
While this is one of the longest-lasting filters available, it really gives
users a workout as they pump.
A few additional considerations not listed in spec charts include:
Effectiveness - All of the filters and purifiers in REI's product mix will knock out larger microorganisms such as giardia and
cryptosporidia. So what do you get for choosing a more expensive filter? Usually a longer-lasting filter medium, cleanability features and maybe
a more efficient pump handle.
Which filter is right for you? Here's a basic guide:
- If you're a recreational backpacker, someone who takes 1 or 2 overnight trips per year, an inexpensive filter will serve you well. Still, be
careful about what type of water you send through it. Make it as clear as possible and the filter will last longer.
- If you visit the wilderness regularly, seek out a field-cleanable model designed to provide years of service.
- People who explore terrain closer to urban areas, at lower elevations and who travel outside the United States and Canada are candidates
for a purifier.
Pore size - A familiar benchmark for determining a filter's effectiveness is to establish that it is a 'point-2 (0.2-micron) filter'.
The number refers to the size of the pores (openings) in a filter medium. It's not a bad gauge, since the smallest bacteria measure 0.2 microns,
yet some microbiologists will tell you it is a simplistic standard.
Factors such as maximum flow rate, minimum wall thickness and adsorptive capacity can influence such a conclusion. Arguments can be made to
show that a 0.3- or 0.4-micron filter can be as effective at trapping the particles as a 0.2-micron filter.
- Tip: Look for 'absolute' pore size (the largest and least effective holes) when evaluating filters, not 'nominal' pore size.
Adsorption - When filter media block particles while clean water streams through, the process is known as 'sieving'. When particles
stick to the media in the manner of a magnet, this is 'adsorption'. Activated carbon, found in some filters and purifiers, is especially
effective at adsorption.
- Some models attach directly to specific water bottles, which is a nice touch. It can prevent a heartbreaking spill in the field.
- If you're visiting places where turbid water is a factor (say, the desert southwest), a cleanable ceramic filter should be tops on
your list. The same goes if you'll be filtering for a group.
- Avoid filtering water in area where animal or human activity is obvious.
Try and filter water from still, clear water
sources. Many microorganisms tend to sink to the bottom of still water; a turbulent stream keeps them suspended.
- Rather than filter directly from the stream or lake, put water in a pot and filter from that. This gives you a chance to examine exactly
how the water looks before you send it through your filter. This helps prevent clogging. If the water is cloudy, let it sit in the pot for an
hour or so, then skim the clearest water off the top.
- Don't save the first few streams of output from your filter. They don't taste as fresh.
- When you clean your portable water filter, recognize you are handling a potentially contaminated object. Don't handle food or
put your hands to your mouth after cleaning your filter.
- Follow the manufacturer's instructions for cleaning and storage. At home, consider pumping a weak bleach-and-water solution through the
filter to sterilize it. If you can disassemble your unit, allow it to dry out completely before storing it.