Test annually for coliform bacteria and nitrates. Dug (shallow) wells are particularly vulnerable to bacterial contamination, while other types of wells with no history of problems may not need testing as often. Test for sodium, sulfates, iron, manganese and lead every three years unless you have had recent problems with any of these contaminants.

If you suspect contamination or if you know that potential pollution sources (farms, landfills, disposal sites, etc.) are located in the vicinity of your well, you should have your water tested more frequently (i.e., twice a year).

If the taste, odor or color of your water changes, or if your family experiences recurrent, unexplained gastrointestinal illnesses, have your water tested.

Have the water supply tested before purchasing a new home or after you have done any construction or remodeling of your home.

A total coliform bacteria test is recommended after you have replaced old pipes or installed a new well or pump. Total coliform is an indicator of septic system problems and poor well construction.

Testing for nitrates is recommended in early months of pregnancy and again after the baby is born.

If your well is located near industrial sites, your water should be tested for toxic metals such as lead, mercury, arsenic and nickel. Unless you suspect that your water is contaminated, routine annual testing for these metals may not be practical since the tests are expensive.