Systems for Making Drinking Water Safe to Sip

Nelson is a former Times medical writer.

Not many things are more important to human life than drinking water. While this is not a problem for most Americans at home, it can be for travelers to countries where sanitation is poor and the quality of the water is questionable.

In fact, unsafe water and inadequate sanitation are the world's leading causes of human illness, according to the World Health Organization.

The best advice for travelers headed to developing regions is to avoid tap water that has not been boiled. Even if the water has been chlorinated at its source, there is no guarantee that it will be germ-free when it reaches the tap. Water-pipe systems may be leaky and allow contamination to enter. And even efficient chlorinating systems can be overwhelmed when heavy rains wash large amounts of contaminants into the water source.

The question is, then, what is the best way to get safe drinking water? And the answer depends upon understanding the methods used to kill or remove harmful microbes.

The great majority of stomach upsets and diarrhea are caused by certain kinds of bacteria and viruses, as well as by parasites called protozoan cysts. There are three ways of ridding water of these organisms: 1) by boiling it, 2) by killing the organisms with iodine or chlorine or 3) by using a filter to remove the organisms.

Most authorities agree that boiling is the surest way to obtain germ-free water. But if boiling is not practical (and bottled water is not available), the next-best way to kill bacteria and viruses (protozoan cysts may not be killed this way) is by adding five drops of 2% iodine to a glass of water and allowing it to stand for 30 minutes. If the water is cloudy to begin with, strain it through a cloth and add 10 drops of iodine.

According to the Centers for Disease Control in Atlanta, chlorine is less reliable than iodine for disinfecting water since chlorine may not kill amoebas and giardia cysts, a protozoa that is a common cause of diarrhea. Passing the water through a filter that is fine enough to catch the cysts--a filter such as those used in some of the new breed of portable travel water purifiers--is the surest way to eliminate giardia, amoebas and other protozoa. Protozoa are larger than bacteria, but if a filter is selected that is small enough, bacteria can also be eliminated. This filter should have pores that are no more than 0.2 microns in size. Such a filter will not catch viruses, which are much smaller. Only iodine can be relied upon to do that.

If none of the above methods of purifying water is feasible, another option is to select a portable water purifier that uses both iodine and a filter to cleanse the water. Some purifiers on the market employ both methods but others do not. Those that do are usually more expensive. One such unit is the PUR Traveler, manufactured by Recovery Engineering, Inc., of Minneapolis. It retails for $59.95.

The PUR Traveler is about the size and weight of a soft drink can. Contaminated water is poured into the top and the traveler forces the water through the unit by pressing a piston. The system combines a microfilter with an iodine treatment that does not leave a bad taste and does not require a 30-minute wait before the water can be consumed. A replaceable purifier cartridge ($20) will make 100 gallons of drinkable water, according to tests conducted at the University of Arizona and Johns Hopkins School of Public Health.

The PUR Traveler isn't the only water purifier on the market. As the number of tourists visiting developing countries grows, manufacturers have sensed that a market exists for these easy-to-use, portable purifiers. But consumers should be careful which one they buy.

In 1987, the Environmental Protection Agency published provisional guidelines to be used by manufacturers for testing water-purifier safety. According to Juanita Wills, an official with the EPA's antimicrobial branch, manufacturers are asked to conduct tests showing that a purifier meets government standards for killing bacteria, viruses and protozoan cysts. The tests usually are conducted in laboratories and paid for by the manufacturer.

EPA guidelines require that water-purifying devices kill or remove high levels of a common bacterial cause of diarrhea, two kinds of viruses (polio and rotavirus, a type responsible for much diarrhea in children), as well as one kind of protozoan cyst. Although not required by the EPA, the test of the PUR device showed that the hepatitis A virus was also killed, according to Charles P. Gerba, professor of microbiology at the University of Arizona.

At present, Wills said, six companies are registered as meeting the guidelines. Their product names are: Portable Aqua, Walbro Water Purifier, Polar Pure, Chlor-Floc Emergency Drinking Water Tablets, Pentapure Water Purification and Disinfectant Resin and PUR Traveler, the device mentioned above. But one catch is that the EPA has not yet concluded the study that will determine whether the guidelines are strict enough.

Not only is it unclear whether the guidelines are adequate, it is not known whether they are being followed to the letter.

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