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.
Return to Table of ContentsWhat Do the Numbers Mean?
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.
Return to Table of ContentsHow Much is too Much?
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.
Return to Table of ContentsGeneral Indicators
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.
Return to Table of ContentsNuisance Contaminants
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.
Return to Table of ContentsHealth Contaminants
Return to Table of ContentsWhere Can I Get Additional Information?
Return to Table of Contents
Publication #: 356-489
The following publications deal with various aspects of household water quality and are available through your local Virginia Cooperative Extension Office:
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