Bromodichloromethane, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Bromodichloromethane and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.

Chloroform, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Chloroform and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy.

Dibromochloromethane, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Dibromochloromethane and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.

Dichloroacetic acid, one of the group of five haloacetic acids regulated by federal standards, is formed when chlorine or other disinfectants are used to treat drinking water. Haloacetic acids and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.

Haloacetic acids are formed when disinfectants such as chlorine are added to tap water. The group of five haloacetic acids regulated by federal standards includes monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic acid.

Radium is a radioactive element that causes bone cancer and other cancers. It can occur naturally in groundwater, and oil and gas extraction activities such as hydraulic fracturing can elevate concentrations.

Trihalomethanes are cancer-causing contaminants that form during water treatment with chlorine and other disinfectants. The total trihalomethanes group includes four chemicals: chloroform, bromodichloromethane, dibromochloromethane and bromoform.

1,2,4-Trimethylbenzene is a chemical intermediate, industrial solvent and component of gasoline, coal tar and petroleum products. In laboratory animal studies, it harms the adrenal glands.

1,3,5-trimethylbenzene is a neurotoxic, volatile chemical found in gasoline, and used as a solvent and paint thinner.

Barium is a mineral present in rocks, soil and water. High concentrations of barium in drinking water increase the risk of cardiovascular disease and hypertension.

Cyanide is a toxic chemical that causes central nervous system and thyroid toxicity. Water contamination is generally the result of metal mining and chemical industry waste, runoff from agriculture and road salts used for melting ice.

Ethylbenzene, a component of petroleum, is a volatile cancer-causing chemical primarily used for production of plastics and rubber. Ethylbenzene is also released from gasoline fuel emissions.

Fluoride occurs naturally in surface and groundwater and is also added to drinking water by many water systems to prevent cavities and support oral health in people.

In 2015, the Department of Health and Human Services updated its recommendation of an optimal level of 0.7 parts per million, or ppm, added to drinking water based on the health benefits of tooth decay prevention. Studies have shown that fluoride added to community water systems at this level reduces dental cavities, especially in children.

And studies have conclusively shown that fluoride in toothpaste and mouthwash can also provide these benefits.

Mercury is a potent neurotoxin that also damages the kidneys and other internal organs. Mercury enters drinking water from industrial pollution, mining wastes and coal-fired power plants.

Methyl isobutyl ketone is a solvent used in coatings and adhesives.

n-Propylbenzene is a constituent of petroleum and coal, used for chemical manufacturing and in textile dyeing and printing.

Xylenes are solvents used in industrial and consumer products, such as cleaning agents and paint thinners. Xylenes cause nervous system damage and may harm developing fetuses.