UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WSG11
Date Signed: May 8, 1978
Revised: April 17, 1998
Revised by: Paul Berger
MEMORANDUM
SUBJECT: Emergency Disinfection of Drinking Water - Boiling
FROM: Victor J. Kimm, Deputy Assistant (signed by Victor J. Kimm) Administrator for
Drinking Water (WH-550)
TO: Water Supply Representatives, Regions I-X
This guidance clarifies how long to boil water during a boil water advisory or other drinking
water emergency. This guidance was prompted by the fact that various agencies have issued
inconsistent instructions on the duration of boiling.
The Office of Ground Water and Drinking Water and the Centers for Disease Control recently
conducted a joint literature review on how long pathogens can survive boiling. On the basis of this
review, OGWDW and CDC recommend that water be brought to a boil for one minute; this will
inactivate all major waterborne bacterial and protozoan pathogens, including Giardia and
Cryptosporidium. Although information about the waterborne viruses is incomplete, hepatitis A virus--
considered one of the more heat-resistant waterborne viruses-is also inactivated by boiling for one
minute. If viral pathogens are suspected in drinking water in communities at elevations above 6562 feet
(2 km), the boiling time should be extended to three minutes. This is because water boils at lower
temperatures with increasing altitude. This guidance was published in Morbidity and Mortality Weekly
Report, vol 43(36): pp: 661-663, 669 (see p. 663); September 16, 1994.
The recommendation of a one minute boil, at or near 100° C, refers to the total time the water
is held at the boiling point. A rolling boil should not be confused with the first sight of dissolved oxygen
being released, which occurs at a temperature far below the boiling point. Some highly resistant
organisms may survive boiling for one minute. However, the presence of a pathogen would be
extremely rare and that level of risk is acceptable.
If the water contains a significant amount of sediment or floating matter, the water should be
strained through a clean cloth into a container to remove the debris before boiling. This treatment,
however, may not remove toxic chemicals or radioactive constituents that may be present in the water.
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WSG11
Date Signed: May 8, 1978
Revised: April 17, 1998
Revised by: Paul Berger
Some data on thermal inactivation is presented below:
Table 1
Microbial Quality of Potable Water in a "Boil Water Order"*
Surviving
Water Temperature Holding Time Standard Plate Count**
°C (Seconds) Per ml
25 0 8,900
30 0 8,700
40 0 7,600
50 0 760
60 0 < 1
70 0 < 1
80 0 < 1
90 0 < 1
100 0 < 1
* Unpublished data: Drs. Martin J. Allen and John Caruthers, EPA, Cincinnati, Ohio
** Municipal water passed through a carbon filter attachment.
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WSG11
Date Signed: May 8, 1978
Revised: April 17, 1998
Revised by: Paul Berger
Table 2
Effect of Boiling on Giardia Cyst Viability*
Additional Initial Surviving cysts after
boiling time Viable cyst count addition to boiling water
(Minutes) (Cysts per field) (Cysts per field)**
0 32 < 1
1 35 < 1
3 33 < 1
5 38 < 1
10 38 < 1
15 35 <1
20 63 < 1
25 46 < 1
30 63 < 1
* Unpublished data: Dr. E. Meyer and A. Bingham.
** Immediately after adding 10 ml of cysts to 9 ml of boiling water, 1 ml of sample was removed,
cooled to room temperature and examined microscopically.
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WSG11
Date Signed: May 8, 1978
Revised: April 17, 1998
Revised by: Paul Berger
SAFE
drinking
water
in emergencies
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WSG11
Date Signed: May 8, 1978
Revised: April 17, 1998
Revised by: Paul Berger
Public Water Supplies
Health departments and officials responsible for
public water supplies use many safeguards to protect
the sanitary quality of your drinking water. However,
this protection may break down during emergencies
caused by natural disasters, sabotage, or enemy
attack. Then the water supplied to your home may be
shut off or become dangerous to use. YOU MUST
THEN KNOW WHAT TO DO TO PROVIDE A
SAFE AND ADEQUATE SUPPLY OF WATER FOR
YOUR FAMILY.
Private Water Supplies
If you have your own source of supply, such as a
well, cistern, spring, or other private source, ask your
health department to inspect it for sanitary quality
and to show you how to keep it safe. Typhoid fever,
dysentery, and infectious hepatitis are diseases often
associated with unsafe water. They are unpleasant
and sometimes fatal. Your health officials would
rather help you keep well than to investigate why you
got sick. If you follow their advice in the
construction and operation of your private supply,
you can have confidence that, under normal
conditions, it is safe to drink. However, under
emergency or disaster conditions, particularly during
floods, these sources may also become dangerous to
use; unless you are assured otherwise by competent
advice, NO WATER CAN BE PRESUMED SAFE
AND ALL WATER SHOULD BE PURIFIED.
Travelers, Campers, Sportsmen
When you are away from the protection of approved
water supplies during periods of traveling, camping,
hunting, or fishing, you must take precautions to
make sure that available water is safe for
consumption. Remember that no matter how clear
and sparkling a brook or mountain stream may look, it
is not always safe to drink. Whenever you must use
drinking water from a source where the purity is
doubtful, ALWAYS PURIFY IT YOURSELF.
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WSG11
Date Signed: May 8, 1978
Revised: April 17, 1998
Revised by: Paul Berger
Emergency Sources—Out-of-Doors
If it is necessary to select an outdoor emergency
water source, remember that water from underground,
such as that obtained from wells or springs, is less
likely to contain contamination harmful to health than
water from surface sources.
However, if underground water is not available, look
next for a creek, stream, lake, or pond—in that order, if
a choice is possible. Avoid water having a dark
color, an odor, or containing floating materials, as any
one of these may indicate heavy pollution. If
possible, surface water should be obtained upstream
from an inhabited area, dipped from below the surface
AND PURIFIED.
Emergency Sources—At Home
If your home supply is interrupted, limited amounts of
water may be obtained by draining the hot water tank
or by melting ice cubes. Also, water may be dipped
from the toilet-flush tank, but this water should be
purified.
When available, water from stock tanks, irrigation
tanks, cisterns, and farm ponds may be used after
proper purification.
Purification
The following simple procedures, requiring the use of
either heat or certain chemicals, and clean containers
to the extent possible, will destroy the usual harmful
germs that may be present in water obtained from
emergency sources.
HEAT
1. Strain water through a clean cloth into a container
to remove any sediment or floating matter.
2. Boil the water vigorously for at least one full
minute.
3. After allowing the water to cool it is ready to use.
If desired, a pinch of salt added to each quart of
boiled water, or pouring it back and forth from one
clean container to another several times, will improve
the taste.
CHEMICALS
If boiling is not possible, strain the water as in Step 1
above and purify with any one of several chemicals
as follows (choice of chemical to use is based on
availability):
after nuclear attack
open water sources such as
streams
EXPOSED TO R[ADIATION]
DETERMINED S[A_J
AVAILABLE Bf
lakes
ponds
uncovered wells
and tanks
RADIOACTIVE FALLOUT SHOULD NOT BE USED
UNLESS [SA]FE BY SPECIALLY TRAINED
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WSG11
Date Signed: May 8, 1978
Revised: April 17, 1998
Revised by: Paul Berger
MONITORING SERVICES AS |_J THE AREA.
------- |