Travel Reference
In-Depth Information
Katadyn® (variety of filters):
www.katadyn.com/chen
Mountain Safety Research® (Hyperflow and Sweetwater Filters):
www.msrgear.com/
Sawyer® Products (Sawyer filters):
www.sawyerproducts.com
The First Need® filter has an absolute pore size of 0.4 microns; the Sawyer® Viral Pur-
ifier has an absolute pore size of 0.2 microns. Both have been demonstrated to remove vir-
usesaswellasbacteria andparasites instudiesconductedfortheEPA.(Sincesuchdevices
remove all microorganisms, they have been called water “purifiers” even though purific-
ation is not synonymous with total disinfection.) First Need® states that the “Structured
Matrix” of its filters removes viruses electrolytically. Data about the removal of poliovir-
us type 1 and rotavirus SA-11 are presented. Sawyer states that its viral purifier removes
viruses and cites data about removal of the bacteriophage Coliphage MS2. However, the
method by which the viruses are removed is not stated.
All effectively remove
Giardia
,
Cryptosporidia
, other parasites, and bacteria (
Table
pores enlarge with use, they may allow passage of small bacteria, such as the
Vibrios
that
cause cholera. After filtration the water must be chemically treated to destroy those organ-
isms, and the manufacturers' websites recommend treatment with iodine or chlorine.
Table 6-2
Size Comparison (Micrometers) of Organisms and Filter Pores
Filter pores
0.3 to 0.4 μm
Giardia
cysts
6.0 μm
Cryptosporidium
cysts
4.0 μm
Bacteria
1.5 to 3.0 μm
Viruses
0.004 to 0.06 μm
Filters are relatively bulky (for backpacking), are somewhat expensive, and can be ob-
structed by sediment in the water. The obstruction can be slowed or prevented with prefil-
ters; but eventually the filter must be removed and cleaned.
Chemical Disinfection Systems
Chemical disinfection systems combined with microfiltration provide the desired fea-
tures of simplicity, speed, small size, lightweight, and reliability for all organisms. Al-
though many chemicals are effective, only preparations that release halides (iodine or
chlorine) are readily available and have been proven by extensive use. Silver compounds
are used in other countries but have not been approved by the EPA for the United States.
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