Emergency
Disinfection of Drinking Water
In times of 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.
Office of Water 4606-M www.epa.gov/safewater EPA 816-F-05-023 September 2005