SANITATION, ARTHROPOD AVOIDANCE, AND WATER DISINFECTION - Medicine for Mountaineering and Other Wilderness Activities - page 72

In1975KahnandVisscherdescribedaprocedurefordisinfectingwaterwithasaturated
aqueous solution of iodine. Iodine crystals (2 to 8 g, USP grade, resublimed) are placed
in a 30 ml (1 oz) glass bottle with a paper-lined, Bakelite cap. (The details are important;
aluminum-lined caps must not be used.) The bottle is filled with water, shaken vigorously,
and allowed to stand for one hour to produce a saturated solution.
Originally, one-half of this saturated solution (15 ml) would be poured into one liter of
water to be disinfected. If the temperature of the water in the 30 ml bottle is 68°F (20°C)
or higher, which can be achieved easily by carrying the bottle in a shirt pocket, the iodine
concentration in the disinfected water would be about 9 mg/l.
If the water has been filtered, a bottle cap of the solution (2 ml) provides an adequate
amount of iodine.
Saturated aqueous iodine solutions have two distinct advantages:
A bottle containing 2 grams of iodine could disinfect up to 2000 liters of water;
If crystals can be seen in the bottom of the bottle, enough iodine for disinfection is
known to be present, so the system is reliable.
This technique for water disinfection has been denounced, even in terms such as “It can
kill you,” because in decanting the supernatant, iodine crystals could be poured into the
water to be consumed. This hazard is insignificant. Iodine is so weakly toxic that three or
four crystals do not produce any symptoms. Individuals who have used this technique ex-
tensively havefoundthatsmallflakesofiodinearecommonlycaughtbysurfacetensionin
thesmallbottle,pouredintothelargebottle,andingestedwithoutproducinganydetectable
ill effects. A jar with a sleeve in its neck to prevent decanting the iodine crystals, marketed
as Polar Pure, is commercially available. On its surface this jar also has a temperature in-
dicator and data for calculating the volume of saturated iodine solution that would contain
8 mg of iodine. However, this jar is too large to comfortably fit into a shirt pocket.
A saturated aqueous solution of iodine has been singled out as being uniquely ineffect-
ive at low temperatures for eradicating Giardia cysts. If microfiltration is used to remove
Cryptosporidia , this question is moot.
One real problem with saturated iodine solutions is the tendency for the water to freeze
andbreakthebottle.(Suchasmallamountofiodineisdissolvedinthewaterthatthefreez-
ing temperature is not significantly lowered.) Leaving an air space in the bottle by not re-
filling it after its last use in the evening would allow the water to expand as it freezes and
prevent breaking the bottle. Alternatively, the bottle must be kept inside a sleeping bag.
(Glass is the only satisfactory container for aqueous iodine solutions.)
Saturated iodine solutions are widely used for water disinfection because they are con-
venient andreliable. Forinformed adults, extensive experience indicates that the method is
safe, although children must not be entrusted with a potentially lethal quantity of iodine.