UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WSG56
Date Signed: August 6, 1990
Revised: July 28, 1997
Revised by: Marc Parotta
MEMORANDUM
SUBJECT: Use of Water Treatment Chemicals and Operation of
Public Water Systems During Emergencies
FROM: Michael B. Cook, Director (signed by Michael B. Cook)
Office of Drinking Water (WH-550D)
TO: Water Supply Branch Chiefs
Regions I - X
This memorandum clarifies EPA's guidance on water treatment chemicals and the
operation of public water supplies during emergencies. Specifically, this guidance addresses
emergency disinfection. Since the Public Water System Supervision Policy Directive Manual is
currently being revamped, I will postpone assigning a number to this guidance document and will
incorporate it into the revised Policy Directive Manual.
Water Treatment Chemicals
States have the authority to control (approve, prohibit, or limit) the use of water treatment
chemicals in public water supplies. We recommend (and nearly all States agree) that direct
additives used in public supplies meet the specifications of National Sanitation Foundation
(NSF) Standard 60. I further recommend that States use NSF Standard 60, in administering their
domestic water supply programs. In all cases, systems must comply with Federal laws and
regulations, including the Safe Drinking Water Act; Federal Insecticide, Fungicide, and
Rodenticide Act; and the Federal Food, Drug and Cosmetic Act.
Operation of Public Water Supplies during Emergencies
Water supply is essential, but only properly disinfected water may be consumed. In an
emergency, when the provision of adequately disinfected water is interrupted, a public water
supply should contact the State immediately for guidance. As an interim emergency measure,
while awaiting State response, we suggest that the system provide the information on emergency
disinfection in EPA Manual of Individual Water Supply Systems. Appendix C, as guidance to its
customers.
I ask that you distribute copies of this guidance (attached) to the States and other
interested parties.
Attachment
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United States
Environmental Protection
Agency
Office of Drinking Water
EPA-570/9-82-004
October 1982
Washington DC 20460
Water
Manual of
Individual Water
Supply Systems
Appendix C
Emergency Disinfection
When ground water is not available and surface
water must be used, avoid sources containing floating
material or water with a dark color or an odor. The
water tank from a surface source should be taken
from a point upstream from any inhabited area and
dipped, if possible, from below the surface.
When the home water supply system is
interrupted by natural or other forms of disaster,
limited amounts of water may be obtained by draining
the hot water tank or melting ice cubes.
In case of a nuclear attack, surface water should
not be used for domestic purposes unless it is first
found to be free from excessive radioactive fallout.
The usual emergency treatment procedures do not
remove such substances. Competent radiological
monitoring services as may be available in local areas
should be relied upon for this information.
There are two general methods by which small
quantities of water can be effectively disinfected.
One method is by 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
waters free of harmful or pathogenic organisms.
When emergency disinfection is necessary, the
physical condition of the water must be considered.
The degree of disinfection will be reduced in water
that is turbid. Turbid or colored water should be
filtered through clean cloths or allowed to settle, and
the clean water drawn off before disinfection. Water
prepared for disinfection should be stored only in
clean, tightly covered, noncorrodible containers.
METHODS OF EMERGENCY DISINFECTION
1. Boiling. Vigorous boiling for 1 full minute
will kill any disease-causing bacteria present in water.
The flat taste of boiled water can be improved by
pouring it back and forth from one container into
another, by allowing it to stand for a few hours, or by
adding a small pinch of salt for each quart of water
boiled.
2. Chemical Treatment. When boiling is not
practical, chemical disinfection should be used. The
two chemicals commonly used are chlorine and
iodine.
a. Chlorine
(1) 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, one should find the
percentage of available chlorine on the label and use
the information in the following tabulation as a guide:
Available
chlorine1
1%
4-6%
7-10%
Drops per quart of
clear water2
10
2
1
Appr. Cone, as
available free
chlorine
5 ppm
4-6 ppm
4-5 ppm
'If strength is unknown, add 10 drops per quart to purify.
2Double amount for turbid 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 palatable 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.
(2) Granular Calcium Hypochlorite. Add
and dissolve one heaping teaspoon of high-test
granular calcium hypochlorite (approximately 1/4
ounce) for each 2 gallons of water. This mixture will
produce a stock chlorine solution of approximately
500 mg/{, 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 solution to
each 12.5 gallons of water to be disinfected. To
remove any objectionable chlorine odor, aerate the
water as described above.
(3) 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.
b. Iodine
(1) Tincture of Iodine. Common household
iodine from the medicine chest or first aid package
may be used to disinfect water. Add five drops of 2
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percent United States Pharmacopeia (U.S.P.) tincture
of iodine to each quart of clear water. For turbid
water add 10 drops and let the solution stand for at
least 30 minutes (appr. 5 ppm).
(2) 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 in the instructions. 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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