From the Illinois EPA:
Properly constructed and maintained water wells can provide many years of trouble-free service, but wells can eventually deteriorate or become damaged and allow surface contaminants to enter the water. In addition, some groundwater can contain one or more chemical substances in levels above health-based standards. In some cases, contamination of the water can be detected by sight, taste or smell; however, many of the most serious problems can only be detected through laboratory testing of the water.
Public water systems are tested regularly for a variety of contaminants. However, if you have a private well, regular testing is your responsibility. Well construction inspection and improvements, such as fixing a crack in a casing, are important steps in keeping your well water safe.
Here are some recommendations that you can follow to help ensure that your well water is safe:
Test your well water at least once a year for bacteria
Water that has become contaminated by human or animal waste can transmit a variety of infectious diseases, including dysentery, salmonellosis, hepatitis, and giardiasis. Symptoms vary, but nausea, vomiting, and diarrhea, with or without fever, are most common. To assess bacterial safety, drinking water is tested for a group of “indicator bacteria” called coliform bacteria. These bacteria do not usually cause disease themselves, but their presence indicates that surface contamination has found its way into the well and disease organisms may also be present. When coliform bacteria are found in well water, the water should be boiled before being used for drinking or cooking, and the well should be disinfected. In cases when bacteria problems cannot be solved, then you may want to look into continuous chlorination treatment.
Test your well water every year for nitrate, and always test the water for nitrate before giving it to an infant
Nitrate is a common contaminant in Illinois groundwater. An elevated level of nitrate is often caused by septic systems, manure storage areas, feedlots, or farm fields near the well. Wells vulnerable to nitrate contamination include shallow sand point wells and large diameter dug or bored wells and wells with damaged, leaking casing or fittings. Well water containing nitrate at levels above the maximum contaminant level established by the U.S. Environmental Protection Agency (EPA), which is 10 milligrams per liter as nitrogen, should never be given to infants less than 6 months old because it can cause a potentially fatal disease called “blue baby syndrome.” In many cases, constructing a deeper well can reduce or eliminate a nitrate problem. If you know, or suspect, that your well water may contain high levels of nitrate,do not boil the water, as this will only concentrate nitrate levels. If nitrates cannot be eliminated from your well water then you may need to look into reverse-osmosis or distillation treatments.
Flush standing water to reduce levels of lead.
Well water in Illinois rarely contains detectable levels of lead. However, lead can enter drinking water through decay of plumbing materials. Homes built before 1986 are more likely to have lead pipes, fixtures and solder. However, new homes are also at risk: even legally “lead-free” plumbing may contain up to 8 percent lead. The most common problem is with brass or chrome-plated brass faucets and fixtures. Exposure to lead at levels above health standards can impair a child’s development, as well as cause a variety of other adverse health effects in both children and adults.
To minimize your exposure to lead in drinking water, run the water until it gets cold before using it for drinking or cooking. This will flush out most of the lead that may have accumulated in the plumbing. Also, never use water from the hot water tap for drinking or cooking. Hot water is likely to contain higher levels of lead. The only way to be sure of the amount of lead in your household water is to have it tested by a certified laboratory.
This information for citizens as well as information for businesses, government and educators can be found at the Illinois EPA website.