Water Filters and Giardia

Kyoto: Hiking from Kibune to Kurama

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Why Not Just Drink the Water?

In the Great Outdoors, there are potentially four dangers of drinkingwater straight from a source (assuming it's freshwater): chemicalpollutants, protozoa and larger parasites, bacteria, and viruses. In thispanel, we will first discuss a few of the methods used in the backcountry to avoid these dangers, then give a briefdescription of the toxins and pathogens found in water, and which methodis best suited to neutralizing each.

Methods of Purification

The oldest (and cheapest) method of purifying water is to boil it. Boiling for five minutes will kill any biological hazards you could expectto find. Most pathogens are actually long dead by the time the waterboils, but the five minute boil will g et them all (remember to add 1minute to this time for each 1,000 feet above 10,000 feet). Boiling willNOT neutralize chemical pollutants. Chemical purification involves the use of iodine or chlorine tokill the nasties in the water. This method is lightweight and relativelyinexpensive, but will not neutralize chemical toxins. In addition, youmust make sure that water at 25 deg. C (75deg. F) sits for 20-30 minuteswith iodine in it for purification to take place. If the water is colder(as it usually is), you will need to let it sit longer - possiblyovernight for cold stream water. Warm the water against your body or evenon your stove if you want it to be purified faster. Once the appropriatetime has elapsed, the "band-aid" taste of iodine can be neutralized with asmall amount of ascorbic acid (vitamin C). Used properly, iodine willkill most protozoa and all bacteria and viruses in water. After prolongeduse, some people develop thyroid problems, so be aware of this potentialside effect. The latest rage in water purification is the use of filters, and alarge number of them are available . There are a couple of things to bear in mind when shopping for filters. First, only a system which includes a n iodine matrix will kill viruses(see below). Second, a filter with pores larger than 0.2 microns - notethe location of the decimal point, as it is important - will let bacteriathrough. The advantages of a filter are quick processing time (don't haveto wait for the pot to boil or the iodine to do its work) andclean-tasting water (no iodine or vitamin C flavor). Some systems alsocontain a carbon filter which will remove chemical toxins. Finally, one system seldom used by hikers, but carried on seagoingboats and possibly sea kayaks, is the reverse osmosis, or RO filter. These systems are bulky, heavy, and expensive, but they will desalinateseawater - a useful thing to be able to do on a lifeboat, for example. Such filters will also remove all biologicalcontaminants, including viruses (viruses are considerably larger than theexclusion limit of the RO filter).

What Might Hurt You

Chemicals in water could include inorganic contaminants (arsenicand other heavy metals) or organic toxins (fertilizers and pesticides, forexample). In general, it is a bad idea to trust any purification systemto remove these, as even small quantit ies could ruin your day in a hurry. The good news is that water sources in the backcountry are seldomcontaminated with appreciable levels of toxic chemicals. Take a good lookat the stream you're about to get water from. Are there fish in it? Isthere algae on the rocks? Crawdads on the bottom? Insects skimming thesurface? Plants growing along the banks? If yes, the water is probablynon-toxic, chemically speaking. If you're hiking in the desert, though,and a trickle of water etching a groove in the rock is bubbling sulfurfrom its barren depths, you should probably avoid it.

There are a number of parasites, both multicellular andunicellular, which live in water. The most common ones in North Americaare Giardia lamblia (see the CDC report later in this panel) andCryptosporidium. A good filter will remove both, and boiling will kill them. Iodine is a reasonable second choice, but is abit chancy in water carrying Crypto. In third-world countries, the numberof parasites in the water is staggering, hence the hackneyed advice,"Don't drink the water." Amoebae can cause dysentery ("Montezuma'sRevenge"), whipworm causes diarrhea and possible complications if nottreated, and roundworms (Ascaris lumbricoides) can be unpleasant, toname a few. In some areas, such as the Philippines and Africa, you shouldtr y to avoid ANY contact with river water, including swimming or washingin unpurified water, as Schistosoma sp. is prevalent in these areas. These tiny parasites bore directly into the skin, entering the bloodstreamand eventually setting up shop in either the intestine or the bladder. If left untreated or incorrectly diagnosed (a common problem, as symptoms only become manifest weeks or months after contact), the complications can be severe. As with Giardia, though, all of these parasites ar e removed by filtration or killed by boiling.

Bacteria are the second smallest pathogens in water, but they canstill be removed by a 0.2 micron filter. One frequently hears about waterbeing tested for Escherichia coli. While strains of this bacterium can be pathogenic, the vast majority are not, and it is, in fact, one of the species required in the intestine for digestion to occur (without bacteria, we would all die). Since it is present in large quantities in sewage, it is a good indicator strain to show when water has been contamina ted with sludge. There are plenty of other bacteria which are happy in the intestine, to the detriment of the host. All are sensitive to iodine treatment, are killed by boiling, and are removed by good filters.

The smallest parasites are viruses (please direct pointlessdebates about whether or not they are "alive" to one of the sci.biogroups). In true wilderness areas, pathogenic viruses are seldom found inwater, but the odds increase with population dens ity and poor sanitationpractices. Ordinary filters DO NOT remove viruses - in fact, LouisPasteur originally defined viruses as "filterable agents," meaning theytraveled easily through a 0.2 micron ceramic filter. Filters which havean iodine matri x will kill viruses ("inactivate" them, if you prefer),and iodine treatment will also work. Boiling is the most reliable way todo away with viruses, though, and is strongly suggested in third-worldcountries. The specific viruses you should worry about in water arehepatitis A, rotaviruses, polioviruses, and echoviruses. All of thesewill cause diarrhea, intestinal cramps, and discomfort about 48-72 hoursafter contact, and complications could range from liver damage (forhepatitis) to aseptic meningitis and encephalitis (for echoviruses), and paralysis or death(for polio). Yes, everyone is vaccinated against polio these days, but ifyou were born before the vaccine, you could have problems with it.

Notes

1) Boiling your water is cheap and easy, and kills all known pathogens. If you can manage the extra fuel necessary, this is the preferred method.

2) In the United States, you will seldom encounter anything in drinkingwater which can kill you (make you sick, yes, but probably not kill you). Be careful, but don't have a heart attack if you accidentally swallow someunpurified stream water. The chances are thousands of times greater thatyou will die in an automobile accident.

3) Anecdotal evidence which you see on the Net should largely be ignored,especially the "I've used X method for 20 years and never had a problem"variety. Since most water is not contaminated to begin with, just aboutany method could appear to work for quite awhile.

4) This introduction was written by Alan Dove and edited by Eugene Miya[well, I studied biological warfare] and Bill Tuthill. All three know thesubject matter, but this information is intended only for generalguidance. Anything that happens to you a s a result of following or notfollowing it is your own damned fault.