When emergency disinfection is necessary, examine the physical condition of
the water. Disinfectants are less effective in cloudy water. Filter murky or
colored water through clean cloths or allow it to settle, and draw off the
clean water for disinfection. Water prepared for disinfection should be
stored only in clean, tightly covered, containers, not subject to corrosion.
There are two general methods by which small quantities of water can be
effectively disinfected. One method is boiling. It is the most positive
method by which water can be made bacterially safe to drink. Another method
is chemical treatment. If applied with care, certain chemicals will make most
water free from harmful or pathogenic organisms.
METHODS OF EMERGENCY DISINFECTION.
Boiling: Vigorous boiling for one minute will kill any disease-causing
microorganisms present in water. The flat taste of boiled water can be
improved by pouring it back and forth from one container to another (called
aeration), by allowing it to stand for a few hours, or by adding a small
pinch of salt for each quart of water boiled.
Chemical treatment: When boiling is not practical, chemical disinfection
should be used. The two chemicals commonly used are chlorine and iodine.
Chlorine and iodine are somewhat effective in protecting against exposure to
Giardia, but may not be effective in controlling Cryptosporidium. Therefore,
use iodine or chlorine only to disinfect well water (as opposed to surface
water sources such as rivers, lakes, and springs), because well water is
unlikely to contain these disease causing organisms. Chlorine is generally
more effective than iodine in controlling Giardia, and both disinfectants
work much better in warmer water.
Chlorine Methods:
CHLORINE BLEACH: Common household bleach contains a chlorine compound that
will disinfect water. The procedure to be followed is usually written on the
label. When the necessary procedure is not given, find the percentage of
available chlorine on the label and use the information in the following
tabulation as a guide.
Available Chlorine (Drops per Quart of Clear Water)
1% -- (10)
4-6% -- (2)
7-10% -- (1)
(If strength is unknown, add ten drops per quart of water. Double amount of
chlorine for cloudy or colored water)
The treated water should be mixed thoroughly and allowed to stand for 30
minutes. The water should have a slight chlorine odor; if not, repeat the
dosage and allow the water to stand for an additional 15 minutes. If the
treated water has too strong a chlorine taste, it can be made more pleasing
by allowing the water to stand exposed to the air for a few hours or by
pouring it from one clean container to another several times.
GRANULAR CALCIUM HYPOCHLORITE.
Add and dissolve one heaping teaspoon of high-test granular calcium
hypochlorite (approximately 1/4 ounce) for each two gallons of water. The
mixture will produce a stock chlorine solution of approximately 500 mg/L,
since the calcium hypochlorite has an available chlorine equal to 70 percent
of its weight. To disinfect water, add the chlorine solution in the ratio of
one part of chlorine solution to each 100 parts of water to be treated. This
is roughly equal to adding 1 pint (16 oz.) of stock chlorine to each 12.5
gallons of water to be disinfected. To remove any objectionable chlorine
odor, aerate the water as described above.
CHLORINE TABLETS.
Chlorine tablets containing the necessary dosage for drinking water
disinfection can be purchased in a commercially prepared form. These tablets
are available from drug and sporting goods stores and should be used as
stated in the instructions. When instructions are not available, use one
tablet for each quart of water to be purified.
TINCTURE OF IODINE.
Common household iodine from the medicine chest or first aid kit may be used
to disinfect water. Add five drops of 2 percent United States Pharmacopeia
(U.S.P.) Tincture of iodine to each quart of clear water. For cloudy water
add ten drops and let the solution stand for at least 30 minutes.
IODINE TABLETS.
Commercially prepared iodine tablets containing the necessary dosage for
drinking water disinfection can be purchased at drug and sporting goods
stores. They should be used as stated. When instructions are not available,
use one tablet for each quart of water to be purified.
WATER TO BE USED FOR DRINKING, COOKING, MAKING ANY PREPARED DRINK, OR
BRUSHING THE TEETH SHOULD BE PROPERLY DISINFECTED.
