Blake Ross, Kathleen Parrott
Virginia Cooperative Extension
Obtaining
a water analysis from a testing laboratory is a necessary first
step toward solving household water quality problems.
Before seeking testing, you may have had concerns about the
safety of the water used in the household. Or you may have noticed
objectionable symptoms when using the water for drinking, cooking,
or other household purposes. Perhaps you have routinely monitored
your household water quality through periodic testing and have
recently noticed differing results between tests for one or
more indicators. To positively identify the source of contamination
problems, as well as to determine the type of corrective action
to take, a properly interpreted water analysis report is essential.
Besides
providing a laboratory report of the analysis for given contaminants,
most water testing laboratories provide little additional
explanation of test results beyond the units used and possibly
a footnote or similar comment in the event that a problem
contaminant is identified. The information provided below,
along with a glossary of water testing terms, may assist you
in understanding a water analysis report for some of the more
common household water quality contaminants.
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Once
a water testing laboratory has completed the analysis of your
water, you may receive a report that looks similar to
Figure 1. It will contain a list of contaminants
tested for the measured concentration of each and will
sometimes highlight any problem contaminants. The concentration
is the amount of a given substance (weight) in a specific amount
of water (volume). The most common concentration unit used is
milligrams per liter (mg/L) which, in water, is approximately
equal to one part per million (ppm), or one part contaminant
to one million parts water. For many chemical compounds and
toxic substances, the units used to measure concentration are
even smaller. In these cases, parts per billion (ppb) is used.
Some contaminants have units that are specific to the test like
those used for radon, hardness, conductance, and turbidity.
Others, such as pH, are expressed as an index number
and not in terms of concentration, and therefore have no units.
Even
with modern techniques and expensive equipment, there are
limits to which a water testing laboratory may determine the
amount of a given contaminant in water. If the amount of a
substance is so small it cannot be measured, the laboratory
will usually indicate that the result is "below detection
limit" (b.d.l.) or "not detected" (n.d.), or it may provide
the actual detection limit value for a given contaminant by
using a "less than" symbol.
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"Pure"
water does not exist in nature and nearly all water contains
contaminants. In most cases, the levels of these contaminants
are minimal and of little consequence. When certain contaminant
levels in household water are excessive, however, they may affect
household activities and/or be detrimental to human health.
Evaluating what levels of contaminants are acceptable and understanding
the nature of problems caused by these contaminants are the
basic considerations in interpreting a household water analysis
report.
Acceptable
limits for evaluating the suitability and safety of a private
water source, such as a backyard well, are available for many
contaminants. Some established standards are set by nuisance
(taste, odor, staining, etc.) considerations, while many are
based on health implications and are legally enforceable with
respect to public water systems. These acceptable limits
should be used as guidelines for your own water supply when
evaluating your test results.
Whether
you have the results of specific tests that you requested,
or you simply instructed the laboratory to conduct general
or routine household water quality tests, you can use the
following tables as a general guideline for the most common
household water quality contaminants. These are divided into
three categories: general indicators, nuisance impurities,
and health contaminants. (Note: Some contaminants are evaluated
on the basis of both nuisance and health criteria.) The limited
discussion accompanying each contaminant will provide you
with acceptable limits and some information about symptoms,
sources of the problem, and the resultant effects.
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General
water quality indicators are parameters used to indicate the
possible presence of other harmful contaminants. Testing for
indicators may eliminate costly tests for specific contaminants.
Generally, if the indicator is excessive, the supply may contain
other contaminants as well, and further testing is recommended.
For example, you are probably familiar with coliform bacteria.
These harmless bacteria are present in the air, soil,
vegetation,
and all warm-blooded animals. A positive total coliform bacteria
test result may be followed by a fecal coliform or E. coli
bacteria test which, if present, would confirm that sewage
or animal waste is contaminating the water. The pH value is
also considered a general water quality indicator which, along
with total dissolved solids (TDS), should not change
appreciably over time. The tests listed in
Table 1, with a test for nitrate
(See Table 4), provide a good routine
(as often as once a year) analysis for most rural water supplies,
unless there is a reason to suspect other contaminants.
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Nuisance
contaminants are another category of contaminants. While
these have no adverse health effects at low levels, they may
make water unsuitable for many household purposes. Nuisance
contaminants may include iron, bacteria, chloride, and hardness.
Table 2 lists some typical nuisance contaminants
you may see on your water analysis report. Acceptable limits
for nuisance contaminants come from the EPA Secondary Drinking
Water Standards
Hardness
is one contaminant you will also commonly see on the report.
Hard water causes white, scaly deposits on plumbing fixtures
and cooking appliances and decreased cleaning action of soaps
and detergents. Hard water can also cause buildup on hot water
heaters and reduce their effective lifetime. Table
3 will help you interpret your water hardness parameters.
Hardness
may be expressed in either milligrams per liter (mg/L) or
grains per gallon (gpg). A gpg is used exclusively as a hardness
unit and equals approximately 17 mg/L or ppm. Those water
supplies falling in the hard-to-very hard categories may need
to be softened. However, as with all water treatment, you
should carefully consider the advantages and disadvantages
of softening before making a purchase.
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The
parameters in Table 4 are some common contaminants
that have known health effects. The table lists acceptable limits,
potential health effects, and possible uses and sources of the
contaminant. In public water systems, these contaminants are
regulated under the EPA Primary Drinking Water Standards. Except
for nitrates, tests for these contaminants are usually only
done when a specific contamination is suspected.
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Further
assistance with interpretation of your household water quality
test report is available. If you have any problems understanding
the way the information is presented on the report, you should
contact the testing laboratory directly for explanation. To
assist you in evaluating the significance of your results, and
any actions you should take to solve identified problems, or
for further information on contaminants not discussed in this
publication, your local Health Department or Cooperative Extension
Office is available. If you wish to obtain more background information
about the occurrence of contaminants and their effects on household
water quality, particularly as it pertains to establishing drinking
water standards, the EPA operates the Safe Drinking Water Hotline
at (800) 426-4791.
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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
The following
publications deal with various aspects of household water quality
and are available through your local Virginia Cooperative Extension
Office:
Household
Water Testing, VCE Publication 356-485.
Home Water Quality Problems--Causes and Treatments,
VCE Publication 356-482
Hydrogen Sulfide in Household Water, VCE Publication
356-488
Lead in Household Water, VCE Publication 356-483
Nitrates in Household Water, VCE Publication 356-484
Bacteria and Other Microorganisms in Household Water,
VCE Publication 356-487
Household Water Treatment, VCE Publication 356-481
Questions to Ask When Purchasing Water Treatment Equipment,
VCE Publication 356-480
Buying Bottled Water, VCE Publication 356-486
Adapted
from the following publications: How to Interpret a Water Analysis
Report by P.D. Robillard, W. E. Sharpe, and K. S. Martin of
Pennsylvania Cooperative Extension, and Water Testing Terms
by M. A. Sward of Oregon Cooperative Extension.
Publication
Number
356-489
,
October 1996
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