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Purifying Water
Three things have to be removed from
wild water to make it
safe for drinking: parasites, bacteria, and viruses. Some of this data comes from: "Medicine for
Mountaineering", 4th ed., James Wilkerson, MD, The Mountaineers, 1992.
Start with the visually clearest water you can find; just to minimize sand,
grit, or any tiny suspended particles. Filter with a bandana or coffee filter
(they don't work that well), or let water stand in a pot for several hours.
Really fine silt may have to sit overnight to settle to the bottom of the pot.
Viruses are more of a Third World problem, not as big an issue in North America
wilderness - but not impossible either.
Boiling
Boiling kills all three. According to the CDC, once the water
has started to boil, the bacteria and parasites are dead. They recommend boiling for
another three minutes to kill viruses. Boiling is time consuming and requires a stove and
additional fuel just for water treatment. When snow camping,
you may have to melt snow to make water, bring plenty of liquid stove fuel.
Iodine Tablets
Iodine tablets kill everything but cryptosporidium which is a
tough skinned parasite. Use 1 tablet per quart unless the water is dirty or very cold then
use 2. It takes about 15-20 minutes for the tablets to work, longer when the water is cold
or dirty. Remember to carefully turn the water bottle
upside down, and partially unscrew the top
to
allow some of the treated water to seep through and around the cap threads. Iodine tablets
provide a strong chemical aftertaste after using them for several days. Citrus drinks can
be used to mask this taste but should be added after the iodine has had the required time
to kill all the micro-cooties. Ascorbic acid interferes with how iodine chemically purifies
the water.
Chlorine Based Tablets
This is an alternative to Iodine.
Don't get the pill dust in your eyes or it can cause permanent eye damage
(according to the bottle). Wash
your hands after treating your water.
Pump Filter
Filtering is done with a ceramic filter with microscopic
passages which will remove all but viruses which are too small for the filter to remove.
Typical filter pores are on the order of 0.2um. Viruses have to be killed with iodine tablets
or boiling. Filters can clog easily and depending on the design, may be difficult to
clean. Try to use water where the silt or sand has already settled to the bottom.
Purifier
Purifiers are ceramic filters which have been impregnated with
an Iodine compound. The filter mechanically removes the bacteria and parasites. Then the
iodine kills any remaining viruses. This is the most effective treatment available. The
amount of iodine is less than what you would get from a tablet and therefore the water
tastes better. Desirable design features in a filter or purifier include: small size and
weight, low force to use, easy to clean, field replaceable cartridge, and a high flow rate
of treated water. These unfortunately are no longer available
- the EPA determined that they were no longer effective. Never heard a good
explanation of why.
UV Light Pen
This is a newer alternative, seems to
work ok as long as you have battery power, the device is working, and the water
is clear.
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