Ask the residents of Jackson Wisconsin about their drinking water and right now you’ll hear a lot of grumbles. 100% of the city’s drinking water comes from groundwater and hasn’t reported any contaminants to the EPA since 2005, although numerous private well owners have not been so fortunate.
The Wisconsin DNR had issued a drinking water advisory in July due to a gasoline leak in the area. A 10 inch fuel pipeline ruptured and released an estimated 54,600 gallons of gasoline which has contaminated 23 private wells. A month after the rupture water samples found 216 parts per billion of benzene, more than 43 times the federal safe drinking water standard, still in the water and residents are relying on bottled water.
It shouldn’t be a surprise that human activities pollute groundwater. Improperly built and/or maintained septic systems and toxic chemicals from underground storage tanks can contaminate groundwater. So can fertilizers, pesticides, road salt and motor oil, all of these products may seep into the aquifers. However, sometimes the quality and safety of groundwater is affected by substances that occur naturally in the environment.
Microorganisms
Bacteria, viruses, parasites, and other microorganisms are sometimes found in groundwater. Coliform bacteria originate as organisms in soil or vegetation and in intestinal tract of warm-blooded animals. This bacterial pollution includes runoff from woodlands, pastures, septic tanks, animals, and water fowl.
Some bacteria are completely harmless, but others can cause illnesses. Parasites can cause illnesses such as Guinea worm or cryptosporidiosis.
Radionuclides
Radon is a natural occurring gas that emits ionizing radiation. It seeps into homes through basement floors 
and can be present in granite countertops.
Uranium is another natural element that can be found within rock, soil, and water. It is the 51st element in order of abundance in the Earth’s crust and the highest-numbered element found in significant quantities on Earth.
Radon in water in itself isn’t serious, but it contributes to airborne radon levels in a home and can increase your family’s risk of lung cancer. Most ingested uranium is eliminated from the body, but some is absorbed and carried through the bloodstream. Elevated levels of uranium from drinking water can the kidneys over time.
Heavy Metals
Arsenic is an odorless and tasteless semi-metallic element that occurs naturally in rock, soil, and water. It is also found in food and air.
Another natural occurring heavy metal is chromium. It is the 24th most abundant element in the Earth’s crust and is found in soil, sea water, rivers and lakes.
Exposure to high-levels of arsenic poses potential serious health risks, it is known as a cancer-causing agent and can is associated with the development of diabetes. Chromium – 3 is a nutritionally essential element in humans, but chromium – 6 is likely to be cancer-causing and at least 74 million Americans in 42 states drink chromium-polluted water.
The Environmental Protection Agency (EPA) strongly encourages people to learn more about their drinking water. It is a requirement for all community water systems to prepare and deliver an annual confidence report (water quality report) to customer by July 1st of each year. Public water systems are required to treat and test drinking water according to federal quality standards, but private well owners are responsible to ensure that their own drinking water is safe.