[pct-l] Filters, Iodine, Chlorine etc.

[Brick Robbins <brick@fastpack.com>]

---If you are paranoid about Giardia, as about 10-40% of the population
should be, then DO NOT use chlorine to dininfect your water. It in
inefective on Giardia. (See the reference below). If you have used chlorine
in the past, and not gotten sick, then you are probably one of the 60-90%
of folks who don't get any symptoms.

---If you use iodine, then you should use a system that measures the water
temperature. Iodine in Cold water can take up to 8 hours to kill Giardia.
The times you read on the bottle of pills is for killing bacteria, not
Giardia.
(See the reference below)

The majority of folks exposed to Giardia do not report symptoms. A large
minority report mild symptoms, and a small minority get hit like a Mack
Truck. 

I know which catagory I fall into and I no longer purify my water in the
mountains.

FWIW, there is a cheap substitute for Flagyl (the antibiotic used in the
USA) that has few side effects, availible in most other countries
(including Mexico) called Tinidizole. IMHO, all through hikers should take
a side trip from San Diego to buy some (just in case). 

For more than you ever wanted to know about this subject see:
http://www.gorp.com/gorp/health/WTRFLFAQ.HTM


======excerpt from ==================
Back-country water treatment to prevent giardiasis. Jerry E. Ongerth, PhD,
PE, Ron L. Johnson, Steven C Macdonald, MPH, Floyd Frost, PhD, and Henry
H. Stibbs, PhD
==================================
Chemical Disinfectants - The effectiveness of seven disinfecting chemical
preparations ranged from only a few percent to greater than 99.9 percent,
depending on the chemical and its concentration, the contact time, and the
disinfectant demand of the water
 (Figure 2).  None of the disinfectants was more than 90 percent effective
after a contact time of 30 minutes.  After eight-hour contact, the four
iodine-based disinfectants, each caused a greater than 99.9 percent
reduction in viable cysts.  The chlorine -based disinfectants were clearly
less effective than the iodine-based ones at both contact times. 


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