1989 by Bill Tuthill
Unpurified drinking water may contain four things that pose health risks: protozoan parasites (e.g. giardia), toxic bacteria, viruses, and poisonous chemicals. Only boiling and iodine are entirely effective against the first three, and only charcoal filtration is effective against the fourth.
Just ten years ago, halazone tablets were the preferred water treatment method. Even today, many commercial rafting companies use Clorox(TM) to disinfect dishes. Both halazone and Clorox are chlorine-based, and because chlorine is unstable, slow to disinfect, and pH-sensitive, it is not always effective against protozoa and viruses. Halazone also tastes worse than iodine, so there's no excuse for using it. US municipal water supplies are usually treated with chlorine, so your tap water may not always be free of micro-organisms.
The First Need(R) water filter is cheap (less than $40), but is effective only against protozoan parasites. Its .4 micron filter pores are smaller than giardia cysts (3.5 microns), but larger than some bacteria. The marketing brochure for the First Need says it removes 99% of cholera and typhoid bacteria, but does not say that E. coli bacteria (which range from .3 to .9 microns) go right through its screen. A few years ago my wife got a case of turista on a Deschutes trip where we filtered all our water through a First Need. (The banks of the Deschutes are heavily grazed, and cattle are prime carriers of E. coli.) The bacteria remained in the filter and she got the same case of turista the next few times we used the filter, until we bought a new one. If you own a First Need, flush it with iodine as soon as you come home. The First Need's charcoal canister is not big enough to be effective against poisonous chemicals -- you need a pound of charcoal for this -- so the charcoal just adds unnecessary weight, and provides a potential haven for the growth of harmful bacteria.
The Katadyn(R) pocket water filter is expensive (around $180), but is completely effective against bacteria as well as giardia. Furthermore, it can be cleaned after it clogs up. When our second First Need clogged up (they lasted only one season for us) we bought a Katadyn. The Katadyn is effective at removing smaller bacteria such as E. coli. However, the Katadyn's .2 micron filter is not effective against viruses. If you travel abroad (to Nepal for example), you risk viral infections such as Hepatitis A and Hepatitis non-A non-B, among others. In the US, most water is not yet contaminated by virus, but there's no reason to believe water supplies will remain uncontaminated for much longer.
To be entirely safe, water should be boiled for at least five minutes. Giardia is killed in less than a minute at 176 degrees, well under the boiling point. Bacteria and viruses last somewhat longer, but are probably killed in less than five minutes at 190 degrees. Some viruses may last longer; nobody knows. At 10,000 feet water boils at 194 degrees, so above this altitude you should boil water an extra minute for each 1000 feet. Very few river trips start this high, however. The main problem with boiling water is that it requires lots of fuel, which may be at a premium on long river trips.
If you have neither the time nor the inclination to boil water, iodine is equally effective. After 10 minutes (20 minutes for very cold water), a sufficient dose of iodine kills all protozoa, bacteria, and viruses. There are many iodination methods, and two excellent ones are commercially available. For low-volume purification, PolarPure(TM) is the best product. After adding water to a bottle containing iodine crystals, you pour a few capfuls into a liter of water and wait 10 minutes. The drawback is that a bottle of PolarPure can purify only 8-10 liters at once. The advantage is that iodine crystals are inert and last a very long time. For high-volume purification, check out Potable-Aqua(TM) tablets. Dissolve one or two tablets in a liter of water and wait 10 minutes. The main problem with iodine tablets is that they degrade upon contact with moisture, so be careful with that bottle, and throw away open bottles when returning home.
An older method, using tincture of iodine, is definitely not a good idea. Tincture contains more sodium iodide than iodine, and because sodium iodide has no disinfectant activity, it unnecessarily increases total iodine consumption.
Although iodine is not highly toxic, continuous ingestion of iodine may cause health problems. A study of Florida prison inmates who consumed iodinated water showed that their pre-existing thyroid conditions got worse. Also, if pregnant women ingest large amounts of iodine, the fetus may get a goiter that could cause respiratory obstruction at birth. The moral of the story is: don't iodinate all your water for more than a few months. The accepted concentration for iodine disinfection is 8 milligrams per liter, but this is mostly to get rid of protozoan parasites. A good compromise would be to filter first, then use a low concentration of iodine to get rid of bacteria and viruses. For this, a concentration of .5 mg/L is deemed adequate, so one capful of PolarPure or one Potable-Aqua tablet should disinfect around 16 liters.
Giardia has become a well-known, almost fashionable, outdoor hazard. Many people who experience gastro-intestinal problems after drinking bad water think they have contracted giardia. In many cases they have contracted something else. Since the only FDA-approved treatment for giardia (Flagyl) is carcinogenic, it's wise to make sure you really have giardia before taking Flagyl. Most low-grade bacterial infections go away on their own, and Flagyl is ineffective against viral infections. Tinidazol may also be available in your are, and is more effective against giardia.
[This information was based on "Medicine for Mountaineering", various owner's pamphlets, and personal experience.]