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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Water Purification

TRAVELERS MUST INCREASE water intake as they expend more energy carrying a pack, walking, museum-going, and being outside. In hot climates the need for water doubles or triples. Hikers require a gallon or more per day as they sweat and respire water and water vapor. Note that alcohol and caffeinated drinks have a dehydrating effect.

Thirst is not a reliable indicator of hydration state. As visible semi-mucous membranes, lips are. The next time yours feel dry or chapped drink several glasses of water and see what happens.¹

Another barometer is urine color. If it's always dark you're probably a liter or two low. A rule of thumb is to drink enough water to ensure at least two clear, healthy pees per day.

Obtaining Safe Water

In Western Europe, much of Eastern Europe, and other developed countries you can drink safely from public water supplies. In many (but not all) developing countries the water supply contains diarrhea-producing bacteria. While some hard travelers adjust to impure water over weeks or months, most travelers avoid discomfort by buying most or all of their water.

Ice cubes in developing countries are rarely made from purified water; they bite even from alcoholic drinks.

Buying water

is usually easy. It is sold in convenient one or 1.5-liter plastic bottles which cost from fifty cents to $3, depending on the country. Look for a quality label and a safety-sealed cap. Bottled drinks are also safe and routinely drunk by travelers.

Boiling

makes tea, coffee, and soups safe in developing countries. Opinion varies on how much boiling is necessary, but a minute or two at full boil should do the job.

Iodine

is the preferred chemical treatment for water. It is easy and effective in twenty minutes, but iodine probably should not be used for months at a time. It also should not be used by pregnant women and people with thyroid conditions. The two most popular iodine treatments in the U.S. are Potable Aqua and Polar Pure.

Potable Aqua

consists of tiny iodine tablets in a small glass bottle. Directions are one or two tablets (depending upon temperature, clarity, and Giardia control) per liter of water. Shake and let dissolve, then loosen the cap and shake again to allow the iodized water to spread over the threads, killing germs there. It's ready for drinking in twenty minutes.

The water has a slight brownish-orange color, and a moderate iodine taste. Potable Aqua also comes with ascorbic acid tablets, called P.A. Pure, which greatly reduce the iodine taste and off-color.

Potable Aqua tablets should be left sealed in the glass bottle until use as they have a limited effective life after exposure to air.

Polar Pure

consists of a four-ounce (120 milliliter) glass bottle with crystallized iodine in the bottom. First, the bottle is filled with several ounces of water, then after a few minutes (time dependent on water temperature--a small thermometer is attached) this bottle is poured into a quart of water to be purified. The crystals remain in the original glass bottle. While Polar Pure is slightly more complicated than Potable Aqua, less iodine is used, and it has a longer shelf life.

Liquid iodine

from a dropper bottle is an alternate method used by some travelers. When faced with suspect water in a restaurant they add two or three drops per glass of water, stir, and wait a few minutes. This is unscientific but seems to work.

Silver

water disinfectant tablets are expensive at about $20 for a packet of forty tablets, which purifies forty liters. Silver is an alternative for those who don't want to use iodine.

Chlorine

tablets or liquid are not recommended as a water purifier, as chlorine is unstable and not always effective. Since it is also associated with a small cancer risk, only use chlorine in a pinch.

Filtering

cleans water mechanically. Special purifying filters may make sense when camping away from campgrounds--say in Central American National Parks, or otherwise in the bush. Travelers in Africa, Asia, Latin America, and the former Soviet Union could also benefit. In the long run you could save money by filtering instead of buying, and certainly spare Earth from hundreds of unrecycled plastic bottles.

Boiling is inconvenient since it requires much time and fuel. While iodine renders water bacteriologically safe, it doesn't remove crud or improve taste. A good filter pumps out good water in a few minutes, and provides a real boost as opposed to drinking boiled or iodine-purified--but horrible tasting--water.