same mechanism is puzzling, and extensive
use of this system has not been associated
with infestations. If microfiltration is used to
remove cryptosporidia, this question is moot.
One real problem with saturated iodine so-
lutions is the tendency for the water to freeze
and break the bottle. (Such a small amount of
iodine is dissolved in the water the freezing
temperature is not significantly lowered.)
Leaving an air space in the bottle by not refil-
ling 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 warm--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 and reliable. For informed adults, ex-
tensive experience indicates the method is
safe, although children must not be entrusted
with a potentially lethal quantity of iodine.
Concentrated Alcoholic Iodine Solutions
A concentrated solution of iodine in 95
percent ethanol could provide a compact
source of iodine for disinfecting large quanti-
ties of water. A solution of 8 g of iodine in
100 cc of ethanol (a fully saturated solution
would contain over 20 g of iodine) would con-
tain enough iodine to disinfect 1,000 liters or
250 gallons of unfiltered water or 2,000 or
more gallons of filtered water. The 8 mg of
iodine needed to disinfect one liter of water
would be present in only 0.1 cc of the solu-
tion; enough iodine for five gallons (twenty
liters) would be contained in 2 cc. Tuberculin
or insulin syringes could be used to accurately
meter such small quantities. This preparation
would be reliable because the concentration of
iodine could only increase if the alcohol
evaporated.
Tincture of Iodine
Tincture of iodine is useful for water dis-
infection because it is so readily available,
particularly in developing countries, or in the
US after a major disaster such as an earth-
quake when gas mains are broken and electri-
cal lines are down. (Tetraglycine hydroper-
iodide is almost equally available from out-
door equipment retailers). The major disad-
vantages of iodine tincture are its taste and its
iodide component. Many have found the io-
dine taste imparted by the tincture to be much
stronger than that of other preparations con-
taining similar quantities of iodine. The U.S.
Pharmacopoeia (USP) standard solution is
two percent iodine and 2.4 percent sodium io-
dide in fifty percent ethanol. (Different con-
centrations are also sold as "tincture.") The
iodide has no disinfectant activity and increas-
es total iodine intake.
Tincture of iodine resists freezing. Also, it
can be used to disinfect skin, but aqueous so-
lutions are just as effective for that purpose
and do not sting. Addition of 0.4 cc of a two
percent solution to a liter of water provides an
iodine concentration of 8 mg/l. A dropper that
dispenses a precise volume should be used.
The tincture must be stored in glass bottles.
CHLORINE DISINFECTION
The effectiveness of chlorine for water
disinfection is well documented. However, the
disinfectant action of chlorine is pH sensitive,
and if organic residues are present, chlorine
combines with ammonia ions and amino acids
to form chloramines, which release chlorine
slowly and inconsistently.
Although most municipal water systems in
North America use chlorine as a disinfectant,
free chlorine levels in the water must be con-
