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

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

Fluoride compounds are salts that form when the element, fluorine, combines with minerals in soil or rocks. Many communities add fluoride to their drinking water to promote dental health.

Bone disease (pain and tenderness of the bones); Children may get mottled teeth

Selenium is a metal found in natural deposits such as ores containing other elements. The greatest use of selenium compounds is in electronic and photocopier components, but they are also widely used in glass, pigments, rubber, metal alloys, textiles, petroleum, medical therapeutic agents, and photographic emulsions.

Hair or fingernail loss; numbness in fingers or toes; circulatory problems

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

Increased risk of cancer

The gaseous or liquid form of chlorine (CL2) is a water additive used by municipal water systems to control microbes. It is relatively inexpensive and has the lowest production and operating costs and longest history for large continuous disinfection operations. Chlorine is a powerful oxidant.

Eye/nose irritation; stomach discomfort

Bromate occurs when bromide in the water reacts with the disinfectant, ozone.

Increased risk of cancer

Chloramine (as CI2) is a water additive used to control microbes, particularly as a residual disinfectant in distribution system pipes. It is formed when ammonia is added to water containing free chlorine. Monochloramine is one form of chloramines commonly used for disinfection by municipal water systems. Other chloramines (di- and tri-) are not intentionally used to disinfect drinking water and are generally not formed during the drinking water disinfection process.

Eye/nose irritation; stomach discomfort, anemia