Portable Water Filters and Water Purification
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.
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.
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 or 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?
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.
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:
In an ideal world, portable water filters or purifiers will be:
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.
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:
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:
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.
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.
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.
Disclaimer: The information presented here is for educational purposes only.
It is not intended to diagnose, treat, or cure disease. If you have any health
or medical concerns, please consult your personal health care professional.
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