Bacteria

Coliform
Private wells should be tested at least once a year for bacteria, by a laboratory that performs an E.coli test when total coliform are present. Test again if there is change in the taste, color, odor or appearance of your water. Coliform bacteria are the most common contaminants found in private water systems.

To ensure protection from bacteria, make sure that your well cap and casing are properly sealed with no cracks or leaks. It has been reported that the presence of earwigs in private well systems can lead to high bacteria counts because of the bacteria harbored in the earwigs' stomachs.

Other Nuisance bacteria
Iron and sulfur bacteria may also be present in well water. Although these organisms do not pose a health threat, they can affect the taste, odor and appearance of water. You may have a nuisance bacteria problem if your water has a rotten egg smell or if you notice slime in the toilet tank. If you suspect a nuisance bacteria problem, try disinfecting the well and water system before testing for iron or sulfur bacteria.

Nitrate

In infants under six months of age, nitrate exposure can cause a serious condition called methemoglobinemia --or “blue-baby syndrome”--in which the nitrate binds with the bloods hemoglobin, thereby preventing the blood from being re-oxygenated. Infants with this condition need immediate medical care because it can lead to coma and death. Nitrate taken in by pregnant women may reduce the amount of oxygen available to the growing fetus. Test for nitrate if a pregnant woman or infant will be drinking the water. There have also been reported cases of this illness in people with compromised immune systems that drank water with high levels of nitrate. Everyone should have their water tested for nitrate at least once. If you live in an area within 1/4 mile of a corn, soybean or vegetable field, you should test your water for nitrate regularly.

Lead

Lead was a component of plumbing solder that was used in homes with copper plumbing installed before 1985. It has also been used in brass fixtures. When water is naturally soft or acidic, lead can leach from solder or brass into drinking water. Wells located near existing or former cherry orchards in Door County may also contain lead.

Copper

Copper is present in plumbing lines in most house-holds. Homes that have new copper plumbing or a naturally-soft water supply are more likely to have copper-contaminated water.

Arsenic

If you live in Brown, Outagamie or Winnebago County, contact your DNR drinking water and groundwater specialist to find out whether your well needs to be tested. An arsenic test may be advised if you live near a landfill that received paint or electronic components.

Pesticides

If your well is located within 1/4 mile of a corn, soybean or vegetable field, you should test your well water for pesticides. You should also consider a pesticide test if your well is within 1/4 mile of an area where pesticides are manufactured, stored, mixed or loaded into application equipment.

The most common pesticide found in Wisconsin’s groundwater is atrazine, which is used to control weeds in corn crops. Atrazine is generally a good first indicator of pesticide contamination in wells that are located near corn fields.