Do You Know What Your Water Test Results Mean?

Posted: December 16, 2011

You recently had your private water supply tested, hoping to gain valuable information about the quality and condition of your water. Upon receiving the water analysis report, you find yourself looking at confusing columns of decimal numbers, abbreviations, and contaminants that are difficult to pronounce. What does this all mean?
Image from Google Images

Image from Google Images

This scenario happens all too often to those with private water supplies, and if that person is unsure as to what the water analysis report means, it will be difficult to make any changes to improve or protect their water supply.

While reports will differ depending on the lab doing the analysis, most will contain some of the same basic features: a list of contaminants tested, their concentrations, and, in some cases, highlight any problem contaminants.  An important feature of the report is the units used to measure the contaminant level in your water.  Milligrams per liter (mg/l) of water are used for substances like metals and nitrates. A milligram per liter is also equal to one part per million (ppm) - that is one part contaminant to one million parts water. About 0.03 of a teaspoon of sugar dissolved in a bathtub of water is an approximation of one ppm. For extremely toxic substances like pesticides, the units used are even smaller. In these cases, parts per billion (ppb) are used. Another unit found on some test reports is that used to measure radon  - picocuries per liter. Some values like pH, hardness, conductance, and turbidity are reported in units specific to that test.

Results of the water analysis report are compared to DEP’s drinking water standards.  Each contaminant that was tested for, have acceptable limits or standards in drinking water. These standards are categorized into Health-based (primary) standards, and Aesthetic (secondary) standards.

Health Based Standards include those contaminants that have known health effects. Examples include total coliform bacteria, E.Coli bacteria, barium, lead and mercury.

Aesthetic standards include contaminants that affect the taste, odor or color of the water. While these have no adverse health effects, they may make water unpalatable, reduce the effectiveness of soaps and detergents, or cause staining. Aesthetic contaminants may include iron bacteria, hydrogen sulfide, and hardness.  Depending on the lab, the analysis report may indicate which of the standards were not met by your water supply and give suggestions or resources for remediation of the problem.

Whether your water is causing illness, stains on plumbing, scaly deposits, or  has a bad taste, a water analysis report identifies the problem and enables you to make knowledgeable decisions about water treatment. Retain your copy of the report in a safe place as a record of the quality of your water supply. If potentially polluting activities occur in your area, you may need a record of past water quality to prove that your supply has been damaged.

Penn State Extension also offers a tool on its website to help with water test result interpretation. The tool is called DWIT (Drinking Water Interpretation Tool) and can be accessed at  Simply type in the results that you received on a water analysis report to the online form, click submit, and recommendations will be given based on those results. 
The Penn State publication Water Tests: What to the Numbers Mean? is also available on the Water Resources website to aid in reading and understanding  your water analysis report.

Some information taken from the Penn State Extension Fact Sheet F103: How to Interpret a Water Analysis Report.