Interpreting Water Test Reports

Posted: June 13, 2010

When a private water well is tested, sometimes the report may be confusing. Here is a simple breakdown of what will be included in the report and how to interpret the results.

Bryan Swistock, Water Resources Extension Specialist, School of Forest Resources, Penn State University

Increased permitting and drilling of Marcellus gas wells has resulted in a dramatic increase in the number of private water wells and springs which have been submitted to water laboratories for testing.  In some cases, this testing is voluntarily conducted by the gas drilling company to document any pre-existing water quality problems in drinking water supplies within some distance of their proposed gas well site (usually 1,000 feet but often 2,500 or even 5,000 feet).  In other cases, the water supply owner may choose to pay for water testing to similarly provide documentation of the cleanliness of their water prior to gas well drilling. 

In either case, water supply owners will receive a water test report from the state-accredited testing laboratory.  These reports can include scientific language, symbols, and acronyms that can be difficult to interpret.  Most reports will contain the following basic information:

• Client and Sample Information - basic information about the location of the water supply (address), type of water supply, person collecting the water samples, and dates of sample collection and lab analyses.

 Analyses - usually on the far left of the report, you will find a column listing all of the water test parameters that were analyzed by the laboratory. The number of parameters can vary from just a few to dozens of tests depending on what was requested by the gas drilling company or the homeowner. There is no required list of parameters which must be tested in relation to gas well drilling.

• Results - The most important information on your water test report are the actual results that the laboratory found for the water sample. The numbers indicate the concentration of each water quality parameter in your water sample. In some cases, the unit of measure for each test will be shown next to the result. In others, the units will be shown in a separate column (as in the example test report). The result for each test should be compared to the drinking water standard for that parameter. Sometimes, a water test result will be reported as “ND” (Not Detected), which means that the lab was unable to detect any of that pollutant with its equipment. Similarly, some results may have a less than sign (<) in front of a number. This result means the sample contained less than the detection level for that test. Detection levels are often set at the permissible drinking water concentration for a particular pollutant. If the less-than symbol (<) appears before a number and the number is equal to the drinking water standard, the water is likely safe to drink for that particular contaminant.

• Units - Concentrations of pollutants are usually measured in water by a unit of weight such as milligrams per liter (mg/L) or an equivalent unit called parts per million (ppm). Parameters which are found in very small amounts may be reported in micrograms per liter (µg/L) or parts per billion (ppb).  Some other parameters, including bacteria, pH, and radionuclides, have unique units.

• Standards - Many laboratories include the specific drinking water standards on the report next to each test result. This allows for an easy comparison of your result with the safe or recommended level for each test parameter.

• Comments - Some water testing laboratories will include a brief explanation of your water test results. Specifically, they often will list those pollutants that did not meet the drinking water standard. Occasionally, these comments will also describe the potential harmful effects of pollutants that exceeded the standard and how these pollutants may be removed from the water.

For more assistance with interpretation of your water test report, refer to the following Penn State Cooperative Extension resources:

Water Tests: What Do The Numbers Mean – a 28-page detailed publication that explains water test reports and the various parameters that may be tested in water.  Available online at:

Drinking Water Test Interpretation Tool (DWIT) – an online form where you to enter your water test results.  Once you submit your results, you will receive a customized interpretation of your results in comparison to drinking water standards.  Available online at:

Finally, Penn State Cooperative Extension will be offering numerous safe drinking water workshops later this summer and fall throughout the Marcellus region of the state specifically to help homeowners interpret water test results and properly manage their drinking water supplies.  Watch our web site ( for more details about these events.