Question:
I asked a question about purifying water in regards to drinkingwater passed thru a filter from a lake that motor boats frequented. If thereis any interest, I'd like to get a general discussion going about waterpurification issues.

There's six basic ways I know of to try and find/purify water (besidesout of the old spigot):

1) Get water from a fast running stream/spring. Preferrably from a source above all known pollution points (e.g. a mountain stream above all known campsites, beaver ponds/homes, factories, etc...) and take your chances with the water as is. Obviously it's getting harder and harder to find places like this.

2) Boil water for 'n' number of minutes (where 'n' = ranges from 7 - 20 minutes).

3) Use a water filtration system i.e. 'First Need', 'Katahdyn', etc.. Most of these filters list which bacteria and pollutants are eliminated.

4) Iodine tablets mixed with water.

5) Small amounts of bleach mixed with water.

6) Solar still (a technique that's not normally very practical).

- What are other methods for purifying water ?- What's your preferred method ?- What kinds of pollutants are we most likely to take in when using the various methods ?- In general what are the pros/cons of the methods listed above ?- Did anyone have any bad experiences with water filters ?- How bad is giardia in the areas where you frequent ?

I'd still like to know peoples thoughts about filtering water were motorboats have frequented.

Answer: Unpurified drinking water may contain four things that pose health risks:protozoan parasites (e.g. giardia), toxic bacteria, viruses, and poisonouschemicals. Only boiling and iodine are entirely effective against thefirst three, and only charcoal filtration is effective against the fourth.

Just ten years ago, halazone tablets were the preferred water treatmentmethod. Even today, many commercial rafting companies use Clorox(TM) todisinfect dishes. Both halazone and Clorox are chlorine-based, and becausechlorine is unstable, slow to disinfect, and pH-sensitive, it is not alwayseffective against protozoa and viruses. Halazone also tastes worse thaniodine, so there's no excuse for using it. US municipal water supplies areusually treated with chlorine, so your tap water may not always be free ofmicro-organisms. Moreover, chlorine is poisonous.

The First Need(R) water filter is cheap (less than $40), but is effectiveonly against protozoan parasites. Its .4 micron filter pores are smallerthan giardia cysts (3.5 microns), but larger than some bacteria. Themarketing brochure for the First Need says it removes 99% of cholera andtyphoid 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 gota case of turista on a Deschutes trip where we filtered all our waterthrough a First Need. (The banks of the Deschutes are heavily grazed, andcattle are prime carriers of E. coli.) The bacteria remained in the filterand 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 iodineas soon as you come home. The First Need's charcoal canister is not bigenough to be effective against poisonous chemicals -- you need a pound ofcharcoal for this -- so the charcoal just adds unnecessary weight, andprovides a potential haven for the growth of harmful bacteria.

The Katadyn(R) pocket water filter is expensive (around $190), but iscompletely effective against bacteria as well as giardia. Furthermore,it can be cleaned after it clogs up. When our second First Need cloggedup (they lasted only one season for us) we bought a Katadyn. The Katadynis effective at removing smaller bacteria such as E. coli. However, theKatadyn's .2 micron filter is not effective against viruses. If you travelabroad (to Nepal for example), you risk viral infections such as HepatitisA and Hepatitis non-A non-B, among others. In the US, most water is notyet contaminated by virus, but there's no reason to believe water supplieswill 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 theboiling point. Bacteria and viruses last somewhat longer, but are probablykilled in less than five minutes at 190 degrees. Some viruses may lastlonger; nobody knows. At 10,000 feet water boils at 194 degrees, so abovethis altitude you should boil water an extra minute for each 1000 feet.Very few river trips start this high, however. The main problem withboiling water is that it requires lots of fuel, which may be at a premiumon long river trips.

If you have neither the time nor the inclination to boil water, iodineis 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 commerciallyavailable. For low-volume purification, PolarPure(TM) is the best product.After adding water to a bottle containing iodine crystals, you pour a fewcapfuls into a liter of water and wait 10 minutes. The drawback is that abottle of PolarPure can purify only 8-10 liters at once. The advantage isthat iodine crystals are inert and last a very long time. For high-volumepurification, check out Potable-Aqua(TM) tablets. Dissolve one or twotablets in a liter of water and wait 10 minutes. The main problem withiodine tablets is that they degrade upon contact with moisture, so becareful 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 iodidehas no disinfectant activity, it unnecessarily increases total iodineconsumption. Actually iodine is an essential human nutrient.

Although iodine is not highly toxic, continuous ingestion of iodine maycause health problems. A study of Florida prison inmates who consumediodinated water showed that their pre-existing thyroid conditions gotworse. Also, if pregnant women ingest large amounts of iodine, the fetusmay get a goiter that could cause respiratory obstruction at birth. Themoral of the story is: don't iodinate all your water for more than a fewmonths. The accepted concentration for iodine disinfection is 8 milligramsper liter, but this is mostly to get rid of protozoan parasites. A goodcompromise would be to filter first, then use a low concentration of iodineto get rid of bacteria and viruses. For this, a concentration of .5 mg/Lis deemed adequate, so one capful of PolarPure or one Potable-Aqua tabletshould disinfect around 16 liters.

Giardia has become a well-known, almost fashionable, outdoor hazard. Manypeople who experience gastro-intestinal problems after drinking bad waterthink they have contracted giardia. In many cases they have contractedsomething else. Since the only FDA-approved treatment for giardia (Flagyl)is carcinogenic, it's wise to make sure you really have giardia beforetaking Flagyl. Most low-grade bacterial infections go away on their own,and Flagyl is ineffective against viral infections. Tinidazol may also beavailable in your area, and is more effective against giardia.

[This information was based on "Medicine for Mountaineering", variousowner's pamphlets, and personal experience.]