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How to disinfect water
All types of water are susceptible to contamination by bacteria, viruses
or protozoans. The main threat from drinking untreated water is the
protozoan Giardia Lamblia, which is transmitted from the faeces or cysts of
humans and animals. Giardiasis can cause cramps, diarrhoea, and vomiting.
Consequently most wilderness travellers will want to disinfect any
untreated water. Whatever method you use, always use the water that is
clearest and freshest possible.
Boiling
Boiling is a simple and effective method of disinfection. To kill most
micro organisms you will need to boil water for approx. 2-3 min. at sea level.
Boiling time will need to increase as altitude is gained, at 1650
meters water will need 5 min. then add 5 min for each additional
1650 meters gained. The drawbacks to boiling as a disinfection method
are: It takes up time and fuel debris isn't removed, the water is left
with a flat taste, the waiting time for the water to cool and protozoan can
live in boiling water for undetermined times.
Chemical Disinfection
Iodine is the most common chemical for backcountry water disinfection,
chlorine's another relatively effective purification method. Both will do
an efficient job of killing bacteria and viruses . Both also make claims of
killing Giardia but research suggests there are too many variables to make
chemical treatment reliable in killing Giardia and larger cysts like
Cryptosporidium (new to Australia, but prevalent in North America).
With any chemical treatment the most important thing is to follow the
manufacturers directions on how to use their product. Before any chemical
treatment allow your water to settle and then filter it through layers of
clothe to remove solid materials which pathogens may be attached to.
Disadvantages of iodine are the taste it will leave in the water, the toxicity
to pregnant women or people with thyroid problems and the limited potency
(replace tablets each year).
Filtering
As the risk of Giardia and cryptosporidium grows There is no doubt that
filtration is the safest and most effective way of treating water. Most
good filters have screens rated to 0.2 microns which will remove most pathogens
and bacteria.
Viruses are smaller than the smallest filter made and need further chemical
treatment to kill them.
Disadvantages to filtration systems are, cost and their inability to filter
viruses.
Unfortunately the rate of confirmed Giardia cases is on the increase, including
WA. It is likely that Filtration or Purification units will become a
stock item in the pack of most bushwalkers in the not to distant future
especially group leaders who have duty of care considerations.
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