How does drinking water cause medical problems for hikers?
Certainly a significant portion of backcountry water is contaminated by disease-causing bacteria, viruses, protozoa, and other organisms that can cause serious disease, including gastrointestinal symptoms such as diarrhea. Man and animals, domestic and wild, carry these pathogenic microorganisms into streams and lakes.
Georgia vista from the Appalachian Trail |
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In a survey published in the Journal of Family Medicine (1993), Appalachian Trail hikers reported a high incidence of diarrhea. Sixty-two percent of respondents reported at least one episode. The majority of the gastrointestinal complaints were general symptoms of gastroenteritis or diarrhea. There were four cases of Giardia lamblia, a protozoan infection. Many of these intestinal upsets were probably related to improper water treatment, with some due to inadequate utensil cleansing.
Since only 7 percent of hikers exclusively drank certified or treated water, it is likely that disease incidence can be markedly reduced by compliance with safe-water rules.
Prevention
City water near trails is safe to drink thanks to filtration, chlorination, and good source sanitation.
Before water treatment was introduced (only in 1880) cities and armies suffered from infectious diseases because they did not understand that typhoid fever, cholera, and other diseases were transmitted by unsafe water. (The army of Tamerlane [circa A.D. 1400] was an exception. He ordered that his troops drink only boiled water. This rigidly enforced order probably allowed them to escape decimating epidemics that plagued others. We don't know whether this command was based upon superstition, magic or pragmatic observation.)
Untreated and possibly unsafe water is still a problem for hikers on the trail.
Trail Purification Methods
What are the advantages and disadvantages of each of the three trail water purification methods—filters, boiling, and iodination?
Boiling is best because all contaminants are effectively destroyed but it takes considerable fuel, effort, and time. Filters are effective in removing all organisms except the smallest viruses. Filtering yields instant potable water but it requires pumping effort, adds weight to the pack, and is fairly costly. Iodination can be effective but it makes the water taste bad. It is only recommended for emergency use, and it requires a certain amount of time, depending on the water temperature. For example, it takes at least 10 minutes in warm weather, and can take up to eight hours in cool weather.
Filters
I must admit that prior to picking up my Katadyn filter in Damascus I occasionally drank untreated water. I must also admit that I arrived in Damascus with backpacker's diarrhea. After that, drinking only water that was filterered, boiled, or iodinated (occasionally), I was free of symptoms.
I strongly recommend that all hikers carry a filter!
How did I choose my filter? I didn't know much about them, so I selected based on small pore size and figured that higher price meant better quality. I bought a Katadyn Pocket Filter, which worked very well and was easily recleanable in the field (which I did weekly). Several other hikers reported similar results.
There are about 15 models available, many of which are sold by REI, which publishes a table giving information about comparative performance. Based upon this and on results from a study entitled"Backcountry Water Treatment to Prevent Giardiasis" by Ongerth, et al., published in a 1989 issue of the American Journal of Public Health, I suggest that the choice can be narrowed down to four models. These are all pump types (gravity models did not perform well in the study). They are: Katadyn PF Pocket Water Filter, PUR Explorer Water Purifier, MSR Waterworks II, and First Need Deluxe Water Filter.
When choosing a filter, consider:
- pump versus gravity type
- filter composition (ceramic, resin, structured matrix, carbon/membrane) and treatment (silver, iodine)
- pore size
- ease of cleaning in the field
- weight
- cost
- output and pumping force
Considering properties, I would value in order of most to least importance: (1) pore size (small is best), (2) ease of field cleaning, (3) weight, (4) cost, (5) chemical treatment, and (6) pumping force. All outputs are about the same. Filter composition is hard to compare.
These are the specs of the filters I recommend:
Katadyn: pore size = 0.2 microns; field cleaning = very easy to clean; weight = 21 oz.; cost = $249; chemical treatment = silver; pump force = 20 lbs.; output = 0.73 l/min., filter = ceramic.
PUR: pore size = 0.3 microns; field cleaning = easy to clean; weight = 20 oz.; cost = $130; chemical treatment = iodine; pump force = 5 lbs.; output = 1.39 l/min.; filter=resin.
MSR: pore size = 0.2 microns; field cleaning = partially field cleanable; weight = 16 oz.; cost = $130; chemical treatment = none; pump force = 10 lbs.; output = 0.98 l/min.; filter = carbon/membrane.
First Need: pore size = 0.4 microns; field cleaning = only the pump is cleanable (not the filter); weight = 15 oz.; cost = $75; chemical treatment = none; pump force = 9 lbs.; output = 1.1 l/min.; filter = structured matrix microscreen.
Although I have listed these in my order of preference, choice among them is difficult and must be based upon personal preferences. I believe that PUR and MSR are effective against Giardia, although they were not tested in the field by Ongerth. Several hikers told me that the inexpensive First Need broke down after only moderate use, and Ongerth suggests that it has a useful life of about 800 pints.
