Bromodichloromethane (BDCM) is a member of a group of disinfection byproducts called trihalomethanes (THMs) that form in water treated with chlorine. The EPA has classified BDCM as a probable human carcinogen.

The EPA classifies chloroform as a probable human carcinogen
based on animal evidence, and there is additional epidemiological
evidence that chloroform may increase the risk of colon and bladder
cancer in humans.

Fluoride is present in nearly all city water due to its dental benefits. Most detections, however, are within the safe limits as fluoride is carefully monitored by the utility.

Lead detections in tap water are usually from old piping and plumbing in your own house. Therefore testing at your own tap rather than at the utility is crucial. Even low levels of lead can damage the brain and nervous system, slow development, and lead to problems with learning, behavior, hearing, and speech.

Coliforms are a group of common bacteria found in soil, water, and the gut and fecal waste of humans and other warm-blooded animals. The presence of Coliform could indicate other issues with your well or well casing. Therefore the EPA recommends testing annually for Coliform and E. coli bacteria.

Though most heavy metals in well water occur naturally, lead is usually from old piping on your property or within your house.
Exposure to lead can also cause anemia and impact the immune
system for both children and adults. The EPA classifies lead as a
probable human carcinogen.

Nitrates have many uses from fertilizers to food preservatives. In drinking water, nitrate may be an indicator of nearby agricultural or septic tank contamination. Particularly infants are vulnerable to nitrates. Testing annually is recommended by the EPA since it's also a good indicator for issues with your well casing.

Arsenic is a naturally occurring element. Long-term exposures to low-levels of arsenic concentrations in drinking water are associated with an increased risk for several types of cancer including bladder, gastrointestinal tract, kidney, liver, lung, pancreas, and skin.