Emergency Disinfection of Drinking Water
En español
EPA 810-F-93-002
July 1993
In times of extreme crisis, local health departments may urge
consumers to use more caution or to follow additional measures. If
local public health department information differs from this advice,
the local information should prevail.
When the home water supply is interrupted by natural or other forms of
disaster, you can obtain limited amounts of water by draining your hot
water tank or melting ice cubes. In most cases, well water is the
preferred source of drinking water. If it is not available and river
or lake water must be used, avoid sources containing floating material
and water with a dark color or an odor.
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 (at altitudes above
one mile, boil for three minutes). 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: When boiling is not practical, chemical disinfection
should be used. 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 or water that is extremely
cold.)
The treated water should be mixed thoroughly and allowed to stand, preferably
covered, 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.
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