U.S. EPA Drinking Water Quality
Problems with drinking water can, and
do, occur.
Actual events of serious
drinking water contamination are infrequent and usually of short duration.
However, treatment problems or extreme weather events may allow
contaminants to enter water supplies. In most situations, contaminants are
found at levels that do not pose immediate threats to public health.
Microbial contaminants (such as bacteria and viruses) are of special
concern because they may cause immediate, or acute, reactions, such as
vomiting or diarrhea. Long-term exposure to some contaminants (such as
pesticides, minerals, and solvents) at levels above standards may cause
gastrointestinal problems, skin irritations, cancer, reproductive and
developmental problems, and other chronic health effects. If a public
water system obtains water from a highly contaminated river, lake, or
ground water well, it may have difficulty treating the water to meet
current safety standards. If contamination poses an immediate health
threat, water suppliers are required by law to notify customers right
away. Any violation of a drinking water standard requires public notice.
Reference: U.S. EPA
Drinking Water Quality
Emergency Disinfection of
Drinking Water
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.
Reference: U.S. EPA Emergency Disinfection of
Drinking Water
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