Interpreting Test Results

The presence of a contaminant in your well water does not necessarily mean your health is in danger. Test reports will usually compare the level at which a contaminant is found to a standard, such as the "maximum contaminant levels" (MCLs) established by the U.S. EPA. Levels greater than these standards can indicate a potential problem with your well water. Visit U.S. EPA's web page to view MCLs and learn about potential health effects. Your local health department also can help to explain the test results, as well as describe the treatments available.

Interpreting Testing Results for Common Contaminants:

Coliform Bacteria: This is not a health threat in itself; it is used to indicate whether other potentially harmful bacteria may be present. State and local health departments look for the presence ("positive" test) or absence ("negative" test) of coliform bacteria. A positive test indicates the well may need to be modified or fixed in some way.

Nitrates: U.S. EPA has established a maximum contaminant level for drinking water of 10 milligrams per liter (mg/L) for nitrates (measured as nitrogen). Infants below the age of 6 months who drink water containing nitrate in excess of the MCL could become seriously ill and, if untreated, may die.

Pesticides/herbicides: The U.S. EPA has set a maximum contaminant level for drinking water of 2 micrograms per liter (µg/L) for alachlor and 3 micrograms per liter (µg/L) for atrazine.

Volatile Organic Chemicals (VOCs): There are many different types of VOCs. See U.S. EPA's web page on MCLs to view maximum contaminant levels for VOCs.