Geoscience Reference
In-Depth Information
Heat Sterilization
Water sterilization by boiling is preferred over any method of chemical disinfection.
This time-
honored method is safe and a sure thing, because disease-causing microorganisms cannot sur-
vive the heat of a sterilizing boil. The CDC (Centers for Disease Control and Prevention) re-
commends that you boil water at a vigorous rolling boil for at least one minute at sea level. At
altitudes above 6,000 feet, they recommend three minutes of rolling boil, since water boils at
lower temperatures as the altitude increases. Some references (Wilkerson 1992, 71) state that,
regardless of elevation, the boiling temperature and the time to reach that temperature are suffi-
cient to kill all pathogenic organisms. Since milk is pasteurized at 160˚F, I tend to agree with
those experts who say that by the time water has reached a full boil, regardless of elevation, it
has long since killed any living organisms, except for prions (mad cow disease, scrapie, etc.),
which are rare and are in a totally different class (not really an organism, per se) and can sur-
vive steam sterilization. Boiled water can be used after cooling (do not add ice, which may be
contaminated), but it takes considerable time and fuel to boil all your drinking water.
Note:
Boiling usually has no impact on chemical or radioactive pollutants, which must be
dealt with by other methods.
Portable Water Filters
There are many different portable water filters on the market. A filter is called a “purifier” if it
is certified to remove protozoa, bacteria, and viruses. Other certified filters may remove only
bacteria or perhaps just cysts. Many home water filters will remove unpleasant tastes and
odors, but will not remove microorganisms.
Read the label, but realize that not all similarly
rated filters perform the same,
nor do all filter manufacturers perform the same tests in the
same manner. You can tell whether a filter's pump is working or whether the filter is clogged,
but you can't tell whether the filter itself is working effectively against organisms. Actual lab
tests to verify microbiological filter function are expensive, and there is no thorough testing
protocol to ensure that all filters are tested in a standardized way by any lab that does the test-
ing. Having personally designed medical intravenous filters, consumer water filters, and com-
mercial filtration systems, I will give you my opinion and recommendations later in this
chapter.
Purifying Filters
Almost any backcountry bacteriological filter, including those not given a “purifier” rating, will
do a good job of removing protozoa and their cysts, like
Giardia
and
Cryptosporidium
. Most