Tom Glanville
Iowa State University Extension
Safe
drinking water is essential to good health. Contaminated water
supplies can carry disease; cause diarrhea, nausea, headaches,
or other ailments; and may lead to more serious problems such
as increased risk of cancer or birth defects.
To help
ensure safe water supplies, operators of public water systems
constantly watch for defects that could allow contaminants
to enter the system. Water samples are analyzed frequently
to ensure that federal drinking water standards for public
water systems are met. Privately owned water supplies are
not monitored by professional operators, so it is up to the
user of these supplies to periodically inspect the system
and test for contaminants to ensure safety.
Well
water quality has been a concern in Iowa in recent years.
The University Hygienic Laboratory (UHL) at the University
of Iowa reports that 35-45 percent of the 12,000 private water
samples tested every year have unacceptable levels of coliform
bacteria. At least 15-20 percent contain concentrations of
nitrate that are unsafe for infants.
The
only way to be sure well water is safe is to periodically
test samples for contaminants. Regular inspection of the well
system also will help identify potential problems. This publication
presents only the basics about water contaminants and how
to test for them. See information section on the back for
more details.
The
two most common contaminants of privately-owned wells are coliform
bacteria and nitrate. Tests for these two contaminants provide
a general indication of drinking water quality. Both tests
are recommended at least once a year, preferably in late spring
or early summer during frequent rainfall.
Coliform
bacteria: Coliforms are naturally-occurring bacteria commonly
found in topsoil, surface water, sewage, and animal wastes.
They cause no observable odor, taste, or color changes in
water, and testing is the only way to determine if they are
present. Although coliform bacteria by themselves generally
do not cause disease, their presence indicates an increased
risk that disease-carrying organisms can enter your water
supply.
Nitrate:
Nitrate is formed by decay of naturally-occurring organic
matter in soil, livestock manure, and human wastes. Excessive
use of nitrogen fertilizers also causes elevated nitrate levels.
Rainfall percolating through the soil dissolves the nitrate
and transports it deeper into the ground. Shallow aquifers
and wells are more likely to be contaminated with nitrate
than deeper ones.
Nitrate
causes no observable odor, taste, or color changes in water,
and testing is the only way to determine if high levels of
nitrate are present. When consumed by infants less than six
months old, nitrate can cause a serious blood disorder known
as infant methemoglobinemia, or "blue baby" syndrome.
Manmade
chemicals: Chemicals such as insecticides, herbicides,
solvents, and petroleum products also can get into the water
supply. Improper storage or disposal, chemical spills, and
excessive use or misapplication of chemicals increases the
risks of finding unsafe levels in a water supply. Health effects
vary widely with the type of chemical and its concentration.
Although
some chemicals (particularly petroleum products) cause a noticeable
odor or color in water, testing is the only reliable way to
determine if most manmade chemicals are present in drinking
water. Costs of testing for manmade chemicals can be high,
so professional consultation is recommended before ordering
tests.
Typical
well defects that can lead to water contamination include:
- missing
or damaged well cap;
- cracks,
corrosion holes, or other openings in the upper 20 feet
of the well casing;
- seepage
of contaminated water along the outside of the well casing,
and
- unusually
low water pressure (less than 20 pounds per square inch
when two fixtures are running).
A nearby
abandoned well that is not properly plugged also can route
contaminants directly into the water supply, as can a septic
system that is poorly maintained or located too close to a
well. Wells less than 20 feet deep also are likely to be unsafe
because groundwater at such shallow depths is vulnerable to
contamination.
For
assistance in identifying and repairing well defects, contact
a county health sanitarian or state-certified well contractor.
What
to test for: There are many potential water contaminants.
It would be very costly, and in most cases, unnecessary, to
test for all of them. Unless a specific problem is suspected,
private well owners often rely on tests for coliform bacteria
and nitrate as general indicators of drinking water safety.
Every private well should be tested for these two contaminants
at least once a year. A commercial lab, county sanitarian, the
University Hygienic Laboratory, or the Iowa Department of Public
Health can advise about other possible tests. To help ensure
accurate test results, be sure to work with a laboratory that
has been certified by the Iowa Department of Natural Resources
for analysis of public water supplies.
When
to test: The best time to test your drinking water is
during late spring or early summer when bacteria or nitrate
are most likely to be present. During those times, excess
runoff and soil moisture can flush contaminants into defects
in your well. If present, pesticides used on the lawn, garden,
or farm fields are most likely to be detected in high concentrations
soon after application.
The
worst time to test for water quality would be during extremely
dry weather or when the ground is frozen. Acceptable test
results in the winter or a very dry season doesn't guarantee
that contaminants won't be present during wet weather.
Where
to sample: The best place to collect a sample is at the
tap you drink from most frequently. If this test shows unsafe
levels, inspect the well and plumbing system for defects and
repair them. Then test again. If problems persist, collect
additional samples at other locations to determine if the
impurities are entering at the well or through the plumbing
or water treatment systems.
Avoid
drawing samples at extremely dirty locations where bacteria-laden
dust could enter the container. Clean indoor locations are
best. If an outdoor location must be used, avoid drawing bacterial
samples from frost-proof hydrants. The buried valve that allows
them to drain and avoid freezing can also allow bacterially
contaminated water to be drawn into the water hydrant.
Always
use a container from the laboratory and carefully follow sampling
instructions. Tests for coliform bacteria require the sample
to be in a sterile container and received by the lab within
48 hours after it has been collected.
How
much do you know?
- The
two most common contaminants of private well water supplies
are coliform bacteria and nitrate. True or false?
- The
best time to test water quality is
- late
spring or early summer when water levels are high.
- during
dry weather
- during
winter when the ground is frozen
- Coliform
bacteria leaves a distinctive "rotten egg" odor in water.
True or false?
- Water
quality can be affected by:
- loose,
missing well caps
- spill
or over application of pesticides near well
- a
poorly maintained septic system
- nearby
feedlot runoff or other concentrated sources of nitrogen
- all
of the above
See
answers at the end of the next section.
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
This
document is Fact Sheet
Pm-1563g
,
a series of the Safe Farm Program, Iowa State University Extension,
Ames, Iowa. Safe Farm promotes health and safety in agriculture.
It is funded by the National Institute for Occupational Safety
and Health (NIOSH #U05/CCU706051-03), Iowa State University,
and a network of groups that serve Iowa farm workers and their
families. Publication date: November 1994.
Prepared
by Tom Glanville, extension agricultural engineer; edited
by Laura Miller, extension communications, Iowa State University
Extension, Ames, Iowa.
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