Geoscience Reference
In-Depth Information
The methods in
table 8-1
have been carefully researched, and are time-tested and effective.
They are safe when the directions are correctly followed. The raw materials used in purification
are inexpensive, but they are
poisonous in concentrated form. Use caution and keep them out of
reach of children.
Table 8-1 Disinfection techniques and halogen doses (All doses added to 1 quart of water)
Quantity for 4 ppm (parts
per million)
Quantity for 8 ppm (parts
per million)
Sterilization technique
Iodine tabs (tetraglycine hydroperiodide; Potable-Agua and
Globaline products)
½ tab
1 tab
2 percent iodine solution (tincture)
5 drops (0.2 ml)
10 drops (0.4 ml)
10 percent povidone-iodine solution
8 drops (0.35 ml)
16 drops (0.70 ml)
Saturated iodine crystals in water (Polar Pure product)
2½ teaspoons (13 ml)
5 teaspoons (26 ml)
Saturated iodine crystals in alcohol
2 drops (0.1 ml)
4 drops (0.2 ml)
(5 percent) 2 drops (0.1
ml)
Household bleach (soldium hypochlorite)
4 drops (0.2 ml)
Halogen concentration Sterilization time in minutes at various water temperatures
41˚F (5˚C) 59˚F (15˚C) 86˚F (30˚C)
2 ppm 240 180 60
4 ppm 180 60 45
8 ppm 60 30 15
NOTE: Recent data indicate that very cold water requires prolonged contact time with iodine or chlorine to kill Giardia
cysts (both disinfectants are ineffective against Cryptosporidium cysts). These contact times in cold water have been
extended from the usual recommendations to account for this and for the uncertainty of residual concentration.
(Source: Adapted from the Wilderness Medical Society Practice Guidelines for Wilderness Emergency Care, 1995)
Treating and Finding Water the Low-Tech Way
With a few simple materials, if you can dig your way to moist soil or find some healthy green
bushes, you should be able to provide yourself with drinking water.
Treating Water
Solar Water Disinfection (SODIS)
The solar disinfection of drinking water (SODIS) is promoted by the World Health Organiza-
tion (WHO), and others throughout the third world, as a viable treatment for disinfecting drink-
ing water and reducing the incidence of waterborne diseases. Health workers stress that boiling,
or chemical treatment like chlorination, is much preferred over SODIS, since boiling is 100
percent reliable at killing pathogens, and chemical treatment is close to 100 percent reliable ex-
cept for hard-to-kill pathogens like
Cryptosporidium
. SODIS is not nearly as reliable as boiling
or chlorination, but since boiling requires fuel or other resources that are often in short supply
in third-world locations, SODIS is promoted as being far better than drinking untreated water.
