Filters vs. Purifiers

Filters vs. Purifiers

Filters work by forcing water through material of a certain pore size which screens contaminants. These are fine for backcountry use in the U.S. and Canada since Giardia is the main contaminant here. (Giardia screening requires a pore size of two microns.) Developing countries, however, may have waterborne viruses, such as hepatitis and polio, which are 0.04 microns or smaller. Thus virus control requires boiling, iodine chemical treatment, or a purifying filter.

The PUR filters listed below, as well as the Sweetwater Guardian with its Viralguard accessory, incorporate iodine matrixes which kill viruses and bacteria without passing much iodine into the water.

According to a Katadyn white paper that appears scientific to this nonscientist, in practice non-purifying filters that screen contaminants to 0.2 microns remove most viruses since viruses usually attach themselves to bigger things, which are then screened. This apparently hasn't impressed real scientists at the EPA, however, so if using a non-purifying filter on suspect developing-world water you probably should add iodine after filtering. While not as much iodine is necessary as with unfiltered water, you still must wait twenty minutes before drinking.

Using Filters

Avoid fast clogging by always using the cleanest available water. If the water is particularly dirty or silt-laden, let it settle in a pot before filtering, and/or use a coffee filter or cloth as a pre-filter. I permanently clogged a not-field-cleanable filter on the second liter drawn from a silty Washington river.

To clean a clogged filter you must carefully follow manufacturer instructions. A grave possibility is contaminating yourself with the nasty bacteria trapped inside the filter. You must also be careful about contamination from the water-source hose. Take care with a ceramic filter since a hairline crack will make it 100% ineffective.

Selection Criteria for Water Filters

If you will be depending on a filter for much of your water field cleanability, pump speed, and ease of use are far more important than a few ounces of weight. A good filter saves you from carrying at least some water, which weighs eight pounds per gallon (or one kilogram per liter). Pump speed lessens the more the filter is used.

Filters with a pore size of one micron or less are good. Smaller pore sizes and smaller filters clog faster. Carbon filters trap pesticides and metals, which for my taste is a worthwhile feature. Ceramic-only filters do not.

For emergency or short periods of developing world backcountry use, filters such as the PUR Voyageur, PUR Scout, and Sweetwater Guardian with iodine cartridge are good choices. If you will be filtering mostly from faucets or sinks (the usual scenario), clogging and pump speed will be less of a problem, so smaller filters should suffice.
If you will be filtering most or all of your water from wells or streams, say in East Africa or the Darien Gap, then you will appreciate having (and essentially require) an easy-pumping, easy-cleaning, full-size filter. You may also require spare cartridges or filtering elements.

A water purifier is not a requirement for developing-world travel. Most travelers buy most of their water and use iodine tablets or drops in a pinch.

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