Q \ EMERGENCY DISINFECTION OF DRINKING
WATER
USE ONLY WATER THAT HAS BEEN PROPERLY DISINFECTED FOR DRINKING, COOKING,
MAKING ANY PREPARED DRINK, OR FOR BRUSHING TEETH
1. Use bottled water that has not been exposed to flood waters if it is available.
2. If you don't have bottled water, you should boil water to make it safe. Boiling water will kill most
types of disease-causing organisms that may be present. If the water is cloudy, filter it through
clean cloths or allow it to settle, and draw off the clear water for boiling. Boil the water for one
minute, let it cool, and store it in clean containers with covers.
3. If you can't boil water, you can disinfect it using household bleach. Bleach will kill some, but not
all, types of disease-causing organisms that may be in the water. If the water is cloudy, filter it
through clean cloths or allow it to settle, and draw off the clear water for disinfection. Add 1/8
teaspoon (or 8 drops) of regular, unscented, liquid household bleach for each gallon of water,
stir it well and let it stand for 30 minutes before you use it. Store disinfected water in clean
containers with covers.
4. If you have a well that has been flooded, the water should be tested and disinfected after flood
waters recede. If you suspect that your well may be contaminated, contact your local or state
health department or agriculture extension agent for specific advice.
(U.S. federal agencies and the Red Cross recommend these same four steps to disinfect drinking
water in an emergency. Please, read the text below for important details about disinfection.)
More information about disinfection
In times of crisis, follow advice from local officials. Local health departments or public water
systems may urge consumers to use more caution or to follow additional measures than the
information provided here.
Look for other sources of potable water in and around your home. When your 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. Generally, flowing water is
better quality than stagnant water.
Examine the physical condition of the water. When emergency disinfection
is necessary, disinfectants are less effective in cloudy, murky or colored water.
Filter murky or colored water through clean cloths or allow it to settle. It is
better to both settle and filter. After filtering until it is clear, or allowing all dirt
and other particles to settle, draw off the clean and clear water for disinfection.
Water prepared for disinfection should be stored only in clean, tightly covered,
containers, not subject to corrosion.
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Choose a disinfection method. Boiling and chemical treatment are two general methods used
to effectively disinfect small quantities of filtered and settled water.
Boiling is the surest method to make water safe to drink and kill
disease-causing microorganisms like Giardia lamblia and
Cryptosporidium, which are frequently found in rivers and lakes.
These disease-causing organisms are less likely to occur in well water
(as long as it has not been affected by flood waters). If not treated
properly and neutralized, Giardia may cause diarrhea, fatigue, and
cramps after ingestion. Cryptosporidium is highly resistant to
disinfection. It may cause diarrhea, nausea
and/or stomach cramps. People with severely
weakened immune systems are likely to have more severe and more
persistent symptoms than healthy individuals. Boil filtered and settled
water vigorously for one minute (at altitudes above one mile, boil for
three minutes). To improve the flat taste of boiled water, aerate it by
pouring it back and forth from one container to another and allow it to
stand for a few hours, or add a pinch of salt for each quart or liter of
water boiled.
If boiling is not possible, chemical disinfection of filtered and settled water collected from a
well, spring, river, or other surface water body will still provide some health benefits and is
better than no treatment at all.
When boiling is not practical, certain chemicals will kill most
harmful or disease-causing organisms. For chemical disinfection to
be effective, the water must be filtered and settled first. Chlorine and
iodine are the two chemicals commonly used to treat water. They are
somewhat effective in protecting against exposure to Giardia, but may not
be effective in controlling more resistant organisms like Cryptosporidium.
Chlorine is generally more effective than iodine in controlling Giardia, and
both disinfectants work much better in warm water.
• You can use a non-scented, household chlorine bleach
that contains a chlorine compound to disinfect water. Do
not use non-chlorine bleach to disinfect water. Typically,
household chlorine bleaches will be 5.25% available chlorine.
Follow the procedure 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
table as a guide. (Remember, 1/8 teaspoon and 8 drops are
about the same quantity.)
Available
Chlorine
1%
4-6%
7-10%
Drops per Quart/Gallon of Clear Water
10 per Quart -40 per Gallon
2 per Quart - 8 per Gallon (1/8 teaspoon)
1 per Quart -4 per Gallon
Drops per Liter of Clear
Water
10 per Liter
2 per Liter
1 per Liter
(If the strength of the bleach is unknown, add ten drops per quart or liter of filtered and
settled water. Double the amount of chlorine for cloudy, murky or colored water or water
that is extremely cold.)
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Mix the treated water thoroughly and allow it 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,
allow the water to stand exposed to the air for a few hours or pour it from one clean
container to another several times.
You can use granular calcium hypochlorite to disinfect water. Add and dissolve one
heaping teaspoon of high-test granular calcium hypochlorite (approximately % ounce) for
each two gallons of water, or 5 milliliters (approximately 7 grams) per 7.5 liters of water.
The mixture will produce a stock chlorine solution of approximately 500 milligrams per
liter, since the calcium hypochlorite has 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 ounces) of stock chlorine to each 12.5 gallons of water or (approximately 1/4 liter to 50
liters of water) to be disinfected. To remove any objectionable chlorine odor, aerate the
disinfected water by pouring it back and forth from one clean container to another.
You can use chlorine tablets to disinfect filtered and settled water. 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 or liter of water to be purified.
• You can use tincture of iodine to
disinfect filtered and settled water.
Common household iodine from the
medicine chest or first aid kit may be
used to disinfect water. Add five drops of
2 percent U.S. or your country's
approved Pharmacopeia tincture of
iodine to each quart or liter of clear water.
For cloudy water add ten drops and let
the solution stand for at least 30 minutes.
You can use iodine tablets to disinfect filtered and settled water. Purchase
commercially prepared iodine tablets containing the necessary dosage for drinking water
disinfection at drug and sporting goods stores. Use as stated in instructions. When
instructions are not available, use one tablet for each quart or liter of filtered and settled
water to be purified.
ONLY USE WATER THAT HAS BEEN PROPERLY DISINFECTED FOR DRINKING,
COOKING, MAKING ANY PREPARED DRINK, OR FOR BRUSHING TEETH
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Summary of Key Points:
Filter murky or colored water through clean cloths or
allow it to settle. It is better to both settle and filter.
Boiling is the surest method to make water safe to drink
and kill disease-causing microorganisms like Giardia
lamblia and Cryptosporidium, which are frequently
found in rivers and lakes.
To improve the flat taste of boiled water, aerate it by
pouring it back and forth from one container to another
and allow it to stand for a few hours, or add a pinch of
salt for each quart or liter of water boiled.
When boiling is not practical, certain chemicals will kill
most harmful or disease-causing organisms. Chlorine
(in the form of unscented bleach) and iodine are the
two chemicals commonly used to treat water.
You can use a non-scented, household chlorine bleach
that contains a chlorine compound to disinfect water.
(Remember, 1/8 teaspoon and 8 drops are about the
same quantity.)
You can use tincture of iodine to disinfect filtered and
settled water. Common household iodine from the
medicine chest or first aid kit may be used to disinfect
water.
Tincture of iodine. For cloudy water add ten drops and
let the solution stand for at least 30 minutes.
Office of Water 4606-M EPA 816-F-06-027 August 2006 www.epa.gov/safewater
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