light.
HEAT
Boiling water is safe and reliable. The
Centers for Disease Control (CDC) and the
Environmental Protection Agency (EPA),
which is responsible for water disinfection
programs in the US, recommend that water be
brought to a rolling boil for one minute to in-
sure parasites are killed. Since water boils at a
lower temperature at higher altitudes, these
agencies recommend boiling water for three
minutes at altitudes above 2,000 meters (6,500
feet).
ALTITUDE BOILING TEMP
Sea Level
100ºC
10,000 ft
90ºC
14,000 ft
86ºC
19,000 ft
82ºC
Boiling is a time proven technique for wa-
ter disinfection that is simple and reliable, but
boiling is inconvenient and time consuming,
particularly for quantities of water larger than
one or two liters. An open fire leaves an un-
sightly residue without heavy, bulky fire pans.
MICROFILTRATION
Concern about cryptosporidia, which
unlike other parasites are resistant to halide
disinfectants, has made microfiltration an es-
sential element of water disinfection. The
Centers for Disease Control and Prevention
(CDC) states that backpacking filters used to
remove these parasites should have absolute
(not nominal) pore size of one micron or
smaller
The following do not "promise the filter
removes cryptosporidium:"
·
Effective against giardia or against para-
sites
·
Carbon filter
·
Water purifier
·
EPA approved
·
Activated carbon
·
Removes chlorine
·
Ultraviolet light
·
Pentiodide resins
The generally available filters have
smaller pore sizes, usually about 0.3 to 0.4
microns. Some of the most widely used filter
and their websites are:
General Ecology (First Need
®
)
http://www.general-ecology.com/
Katadyn Products
http://www.katadyn.ch/site/ch_en/home/?L=
en
Northern Mountain Supply (SweetWater)
http://www.northernmountain.com/dept/HC
Mountain Safety Research (MSR)
http://www.msrcorp.com/
PUR/Exstream Products
http://www.purwaterfilter.com/expor.html
Sawyer Products
http://www.sawyerproducts.com/
These filter pores are much too large to re-
move viruses. In fact, as the pores enlarge
with use, they probably allow passage of
small bacteria, such as the vibrios that cause
cholera. After filtration the water must be
chemically treated to destroy those organisms.
Many filter incorporate an iodine contain-
ing resin to destroy viruses (optional for some
filters). Such products are effective but have
