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Understanding Your Water Test Results

Help interpreting your drinking water test results from the lab.

Looking at PapersGetting your water samples to a certified drinking water lab for testing is a big step - but then what do you do with the results?  Interpreting the paperwork the lab sends you can be difficult, but don't worry, there are numerous resources available to help you fully understand your water test results.

Inletkeeper staff can also help to answer questions regarding the results of your water test. Call us to set up an appointment or come by our office during regular business hours.

Reporting Terms, Abbreviations and Units

To better understand how to read the results of your water test, it helps to know a few key abbreviations and unit of measurement used in the report, as well as what some of the specialized terms mean.

The Parameter indicates which water quality parameter is being reported on in that line.

The Result column lists the results from the test for each water quality parameter. Sometimes it is listed in number form. Other times it is listed as “PASS” or “FAIL” or as <MRL.

“PASS” indicates that the amount of that contaminant present does not exceed harmful levels;

“FAIL” indicates that it does. The PASS/FAIL form of measurement is only used for bacteria testing because bacteria are measured on a presence versus absence basis.

MRL stands for Method Reporting Limit. <MRL means that the amount of contaminant present is less than the lab instrument used to measure it could detect.

MCL stands for Maximum Contaminant Limit. The MCL column displays the amount in which the contaminant measured should not exceed. Should your results indicate that you water contains a greater amount of contaminant than listed in the MCL column, your water could be harmful to your health. In cases where the results are greater than the EPA designated MCL, you will notice that there is an “H” in the Flags column.

Units for water tests are generally presented in milligrams per liter (mg/L) or micrograms per liter (ug/L). Another way to reference those would be in parts per million or parts per billion, respectively.

Example of Water Test Results (Analytica Group)

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Interpreting Your Results

Now that you understand how to read the lab report, what do you do with this information? The first thing people may be concerned about is if any of the parameters received a flag for being above the EPA recommended limit. This is definitely something to pay attention to, as treatment of some kind will generally be recommended.

In addition to exceeding the contaminant limits with human health concerns, also look at the other parameters like the pH and Langlier Index. These parameters do not have recommended levels by the EPA, but may cause problems like corroding pipes, scaling or enabling heavy metals like copper and lead to enter your drinking water.

The University of Montana has a great publication that lists parameters, the ranges of potential values, and a clear interpretation of each.  Check it out here and get a better idea of your water quality.  Also, the Penn State Cooperative Extension has a great resource for understanding what the numbers mean here.

In some cases, if the result level is close to but does not exceed the recommended level, you may want to consider testing again at a future time to monitor the situation.

Presentation - Understanding Your Water Test Results

Cook Inletkeeper's presentation about interpreting test results.

Understanding Your Water Test Results

Additional Resources

Water Systems Council Factsheet - Understanding Drinking Water Test Results