Coliforms are bacteria that are naturally present in the environment and used as an indicator that other, potentially harmful, bacteria may be present. Coliforms found in more samples than allowed is a warning of potential problems.

Not a health threat in itself; it is used to indicate whether other potentially harmful bacteria may be present5

Arsenic is a semi-metal element in the periodic table. It is odorless and tasteless. It enters drinking water supplies from natural deposits in the earth or from agricultural and industrial practices. Approximately 90 percent of industrial arsenic in the U.S. is currently used as a wood preservative, but arsenic is also used in paints, dyes, metals, drugs, soaps, and semi-conductors. Agricultural applications, mining, and smelting also contribute to arsenic releases in the environment.

Skin damage or problems with circulatory systems, and may have increased risk of getting cancer

Nitrates and nitrites are nitrogen-oxygen chemical units which combine with various organic and inorganic compounds. The greatest use of nitrates is as a fertilizer. Once taken into the body, nitrates are converted to nitrites.

Infants below the age of six months who drink water containing nitrite in excess of the MCL could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue-baby syndrome.

Trihalomethanes occur when naturally-occurring organic and inorganic materials in the water react with the disinfectants, chlorine and chloramine.

Liver, kidney or central nervous system problems; increased risk of cancer

Carbon tetrachloride is a clear heavy organic liquid with a sweet aromatic odor similar to chloroform. Most carbon tetrachloride is used to make chlorofluorocarbon propellants and refrigerants, though this has been declining steadily. It has also been used as a dry cleaning agent and fire extinguisher; in making nylons; as a solvent for rubber cement, soaps, insecticides, etc.

Liver problems; increased risk of cancer

Haloacetic acids occur when naturally-occurring organic and inorganic materials in the water react with the disinfectants, chlorine and chloramine.

Increased risk of cancer

Dichloromethane, also known as DCM and methylene chloride, is a volatile organic and colorless liquid chemical with a sweet, pleasant odor like chloroform. The greatest use of DCM is as a paint remover. Other uses include: solvent and cleaning agent in chemical manufacture, textiles, electronics, metals and plastics, pesticides industries; blowing and cleaning agent in the urethane foam industry; fumigant for strawberries and grains, and as degreener for citrus fruits; in pharmaceuticals and as an anesthetic; in extraction of caffeine, cocoa, fats, spices and beer hops; as a heat transfer agent in refrigeration products.

Liver problems; increased risk of cancer

Benzene, a volatile organic chemical, is a clear, colorless aromatic liquid. It is highly flammable. It is formed through natural processes, such as volcanoes and forest fires. It is also formed from industrial processes. Benzene is also a natural part of crude oil, gasoline and cigarette smoke. The greatest use of benzene is as a building block for making plastics, rubber, resins and synthetic fabrics like nylon and polyester. Other uses include: as a solvent in printing, paints, dry cleaning, etc.

Anemia; decrease in blood platelets; increased risk of cancer