Kathleen Parrott, Blake Ross, Janice Woodard
Virginia Cooperative Extension
A common hazard of household water is contamination by potentially
harmful bacteria and other microorganisms. Short term gastrointestinal
disorders and illnesses such as gastro-enteritis, giardiasis,
typhoid, dysentery, cholera, and hepatitis have been linked
to water contaminated by microorganisms. The microorganisms
which find their way into a water supply can come from a variety
of sources including sewage, animal wastes, or dead and decaying
animals.
Public
water systems are required by state and federal governments
to provide biologically safe water. However, the safety of
a privately-owned, individual water supply such as a backyard
well rests in the hands of its owner.
How
can an individual tell if household water is contaminated
with bacteria?
Bacteria
in water cannot be seen, tasted, or smelled and many health-related
symptoms are not immediate. Therefore, the only way to reliably
determine if water is contaminated is by a laboratory test.
Testing a water supply for a specific disease causing organism
can be expensive. Handling and culturing disease organisms
requires special training and equipment. Instead, water supplies
are usually tested for the presence of coliform bacteria.
These bacteria are always present in the digestive systems
of humans and animals, and can be found in their wastes. Coliform
bacteria are also present in soil and in plant material. Most
of these bacteria do not cause disease. They are simply an
indicator that the water supply is contaminated and that disease-causing
bacteria may be present.
The
test for the presence of coliform bacteria is relatively inexpensive
and easy to perform. The standard test is called total coliform.
The Federal goal for total coliform in public drinking water
is zero. Water samples that contain any coliform bacteria
are generally reported as "total coliform positive."
Federal
regulations now require that public drinking water found to
be "total coliform positive" must be analyzed with a fecal
conform test. Fecal coliform bacteria are present only in
human and animal waste. It is unacceptable for fecal coliform
bacteria to be present in any concentration.
What
specific test(s) should be done?
Private
water supply users interested in evaluating the bacteriological
safety of the water should contact a Virginia-certifled water
testing laboratory. Upon submitting a water sample, request
a total coliform test to be followed by a fecal coliform test
if the initial test of the sample is "total coliform positive."
Tests for specific bacteria may be required if the water supply
is suspected as the cause of a diagnosed illness among users.
When
should a test be done?
The
Virginia Department of Health recommends that private water
supplies be analyzed for total coliform at least once a year.
If you are considering buying property with a private water
supply, always request a total coliform bacteria test. Testing
is also recommended when any of the following conditions apply:
- there
is an infant in the home;
- a
new well is constructed;
- flooding
occurs near the well or spring;
- any
person or animal becomes sick from a suspected waterborne
disease; or
- the
water supply system on a well or spring has been disassembled
for repairs to components such as the well itself, pump,
pressure tank, treatment devices or pipe lines.
What
should I do if my water is contaminated with bacteria?
First,
don't panic! You have probably been drinking this water for
some time with no ill effects and could possibly continue
to do so. While you and your family may have developed some
immunity to harmful bacteria present in the water, there is
no assurance that you won't suffer ill effects in the future
as a result of continued exposure. Further, guests in your
home who do not have this immunity may experience more immediate
problems.
Learning
that your water supply has been found to be contaminated with
bacteria should encourage you to take action. So that you
can prevent a potential problem from getting worse, you need
to identify the possible source(s) of contamination and take
corrective steps to purify the contaminated water.
What
should be done to eliminate contamination in household water?
Household
water from surface water supplies streams, ponds, and cisternsis
especially susceptible to contamination and, in most cases,
should be continuously disinfected, as described later in
this publication. Additional treatment, such as sedimentation,
coagulation, and filtration, may be needed to provide a suitable
supply of water.
According
to the U.S. Environmental Protection Agency, septic systems
are a major source of contamination of an underground water
supply (well or spring). Inappropriate sitting of drainfields,
and poor design, construction, and maintenance of septic systems,
coupled with improper well and spring box construction, can
lead to contamination of household water. At a minimum, having
your septic tank pumped out every three to five years is recommended
to reduce the probability of contamination.
Preventing
the direct entry of surface water to a well or spring
is an important option to consider to protect the supply from
contamination with bacteria. It is important to remember that
the groundwater supply itself may not necessarily be contaminated,
rather the well or spring, if improperly constructed, may
be funneling contaminants from or near the land surface down
into the groundwater.
A properly
protected well is evidenced by the well casing extending 12
inches or more above the surface of the ground and the ground
sloping away from the well to prevent surface water from collecting
around the wellhead. The top of the casing should have a tight-fitting
sanitary well cap. Additional protection from surface drainage
should be provided by sealing the casing with cement grout
to the depth necessary to protect the well from contamination.
Springs
are particularly susceptible to bacterial contamination since
they are generally located in surface water drainage ways.
A properly protected spring is developed underground and the
water channeled to a sealed spring box. At no time should
the water be open to the air at the surface.
Other
measures to take are: 1) keep all animals away from the
well or spring area; 2) keep the plumbing system clean.
Any time work is performed on the plumbing or pump, the entire
water system should be disinfected with chlorine, as described
below. Simply pulling the pump out of the well, setting it
on the grass to work on it, and returning it to the well is
enough to contaminate the water supply with bacteria.
How
can safe drinking water be made temporarily available while
the source of contamination is being found and eliminated?
Boiling
water is an extremely effective means of disinfection. Boiling
your water continuously for 15 minutes will kill all bacteria.
You could also purchase bottled water or use water from another
source known to be safe for drinking and cooking.
Fresh
liquid chlorine bleach containing 5.25 percent available chlorine
(commonly found in grocery stores for laundry and other household
purposes) can be added to a gallon of drinking water on an
emergency basis. If the water is clear, add 8 drops of bleach;
if the water is cloudy, add 16 drops. Mix bleach in water
thoroughly and let stand for 30 minutes before drinking.
How
can the water supply be made safe to drink after the source
of contamination has been eliminated?
The
Virginia Department of Health recommends cleaning and sanitizing
a contaminated well or spring, and the entire plumbing system,
by shock chlorination. See
directions. This treatment introduces high levels of chlorine
in the water. Chlorine compounds are usually added to the
water in solution form. The chlorine added may be fresh liquid
chlorine bleach (sodium hypochlorite), containing 5.25 percent
available chlorine, or soluble tablets or powder used for
disinfecting swimming pools (calcium hypochlorite), containing
about 70 percent available chlorine.
If you
have water treatment equipment, such as a water softener,
iron filter or sand filter, check the manufacturer's literature
before shock chlorinating to prevent damage from strong chlorine
solutions. Disconnect or by-pass carbon or charcoal filters
during shock chlorination because the process will use up
the capacity of these filters.
Be
careful when handling concentrated chlorine solutions.
Wear rubber gloves, goggles, and a protective apron when handling
chlorine solutions. If it accidentally gets on your skin,
flush immediately with water.
Never
mix chlorine solutions with other cleaning agents or ammonia
because toxic gases may be produced.
Do
not use "fresh scent" or other chlorine bleach containing
perfumes, "all fabric" bleaches or fabric softeners. Plain
chlorine laundry bleach should be used for disinfecting water.
Chlorine solutions lose strength while standing or when exposed
to air or sunlight. Make fresh solutions frequently to maintain
effectiveness.
Wait
one to two weeks and retest your water for bacteria. Before
retesting, check to be sure there is no chlorine left in the
well or spring system using an inexpensive chlorine test kit
(usually available at pool supply stores). If shock chlorination
and measures to prevent contamination do not eliminate the
bacteriological problem, continuous disinfection may be necessary.
How
can water be continuously disinfected?
Most
household water can be disinfected continuously by chlorination,
distillation, ultraviolet light, or ozonation. There is
no ideal disinfection method; each has its advantages
and limitations.
Chlorination
is widely used to disinfect water because it destroys bacteria
within a reasonable contact time and provides long term protection.
Chlorine, readily available at a low cost, is easy to handle
and is also effective in controlling algae.
Chlorine
also has its limitations. Its solutions are only moderately
stable, and organic matter as well as iron and manganese can
interfere with the action of chlorine. Low levels of chlorine
normally used to disinfect water are not an effective treatment
for the parasite Giardia. A relatively high chlorine
level must be maintained for at least 30 minutes to kill Giardia.
High chlorine concentrations can have objectionable tastes
and odors, and even low chlorine concentrations react with
some organic compounds to produce strong, unpleasant tastes
and odors. Chlorinators, although simple to operate, require
regular refilling with chemicals.
The
heat necessary for water distillation is very effective
in killing disease-causing microorganisms. One of the benefits
of distillation is that it uses no chemicals. Distillation,
however, takes longer to produce the processed water than
some other methods, units can be expensive to operate, and
the length of time distilled water is stored can affect its
quality. Distilled water has a very "flat" taste.
Ultraviolet
light is a very effective disinfectant. This method disinfects
water without adding chemicals. Therefore, ultraviolet light
disinfection units do not create any new chemical complexes,
do not change the taste or odor of the water, and do not remove
beneficial minerals from the water.
Ultraviolet
light disinfection also has its disadvantages. This disinfection
technique is more effective against bacteria than against
viruses and parasites such as Giardia. There is no
simple test to determine whether or not the system is providing
proper disinfection. Ultraviolet light devices are most effective
when water is clear and allows the light to easily pass through.
Therefore, ultraviolet light devices are often combined with
other treatment devices such as mechanical filters, activated
carbon filters, water softeners, and reverse osmosis systems
to provide complete water quality solutions. Safety features,
such as detectors that activate audio and visual lamp alarms
in case of lamp failure, are available to ensure that adequate
disinfection conditions are maintained.
Ozonation
uses ozone which is a more powerful disinfectant than chlorine.
Ozone produces no tastes or odors in the water. However, as
a gas, ozone is unstable and has a very short life so it must
be generated at the point of use.
Even
if tests confirm that you have a bacteriological problem,
before investing in expensive equipment, have your household
water supply inspected by a County Health Department official.
More information
For more information about providing biologically safe household water, contact your local Cooperative Extension or Health Department Office.
Acknowledgement
The authors wish to thank the following individuals who reviewed this publication:
Allen Hammer and Robert Hicks, Virginia Department of Health, Richmond
Robert Custard, Regional Sanitarian, Virginia Department of Health, Manassas
Helen Smith, Extension Agent, Rappahannock County
Disclaimer
and Reproduction Information: Information in NASD does not represent
NIOSH policy. Information included in NASD appears by permission
of the author and/or copyright holder. More
NASD Review: 04/2002
Kathleen
Parrott, Extension Specialist, Housing
Blake Ross, Extension Specialist, Agricultural Engineering
Janice Woodard, Retired Extension Specialist, Home Management
and Equipment.
Publication
Number
356-487
,
October 1996
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