Interpreting Your Water Test Report

  • Parrott, Kathleen;
  • Ross, Blake

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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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What Do the Numbers Mean?

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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How Much is too Much?

"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 Indicators

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

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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Health Contaminants

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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Where Can I Get Additional Information?

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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Publication #: 356-489

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.

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