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Drinking Water Contaminants

Regulated Drinking Water Contaminants

The Tracking Network contains information about the levels of several regulated contaminants and unregulated contaminants in drinking water. The contaminants include natural and man-made substances. They get into community water supplies in a variety of ways. These regulated contaminants were selected for the Tracking Network because they occur more frequently in drinking water than other contaminants, and at levels that may affect public health.


Arsenic is a toxic chemical element that is found naturally in the Earth's crust in soil, rocks, and minerals. The levels of arsenic found in drinking water systems and private water supplies across the United States vary widely. Some people could experience skin damage or problems with their circulatory system and may have an increased risk of getting cancer if over many years they drink water that contains arsenic in excess of the EPA standard. The maximum containment level for arsenic is 10 µg/L.


Atrazine is a widely used herbicide for control of broadleaf and grassy weeds. Atrazine is a chemical that may be found in some public or private drinking water supplies. Atrazine potentially causes health effects from both short- and long-term exposures. The maximum containment level for atrazine is 3 µg/L.

Di(2-ethylhexyl) phthalate (DEHP)

Di(2-ethylhexyl) phthalate (DEHP) is a man-made chemical. DEHP is not toxic at the low levels usually present in the environment. Exposure to DEHP is generally very low. The maximum containment level for DEHP is 6 µg/L.

Disinfection By-products (DBP)

DBPs are a family of chemicals formed when disinfectants used to kill viruses and bacteria in community water supplies react with naturally occurring organic matter and other substances in the source water. The risk of illness from DBPs is much lower than the risk of illness from drinking most surface water and some groundwater sources that have not been disinfected. When people consume DBPs at high levels over many years, they increase their risk for health effects. Read EPA’s DPA rules.


Nitrate and nitrite are nitrogen-oxygen molecules that can combine with various organic and inorganic compounds. Nitrate is the form commonly found in water, often in areas where nitrogen-based fertilizers are used. The greatest use of nitrate is as a fertilizer. The risks of exposure to excessive levels of nitrate apply to infants. The maximum containment level for nitrate is 10 mg/L.

Tetrachloroethylene (PCE)

Tetrachloroethylene (PCE), also known as perchloroethylene and tetrachloroethene, is a man-made, colorless, dense liquid. PCE has been found in surface water and groundwater at many locations across the United States; however, the levels of this chemical are too low to be measured at most of these locations. Because of the low levels of PCE, scientists cannot accurately determine how much is present. PCE is not life threatening unless people intentionally or accidentally drink more than a few spoonfuls at one time or spill a large amount so that they breathe it and get it on their skin. The maximum containment level for PCE is 5 µg/L.


Radium is a naturally occurring radioactive metal that can exist in several forms. Radium is present at very low levels in rocks and soil and may strongly attach to those materials. Everyone is exposed to low levels of radium in the air, water, and food. There is no clear evidence that long-term exposure to radium at the levels that are normally present in the environment is likely to result in harmful health effects. However, exposure to higher levels of radium over a long period of time may result in harmful effects. The U.S. Environmental Protection Agency (EPA) and the National Academy of Sciences Committee on Biological Effects of Ionizing Radiation have stated that radium is a known human carcinogen. EPA has set a drinking water limit of 5 picocuries per liter (5pCi/L) for radium-226 and radium-228 combined.

Trichloroethylene (TCE)

Trichloroethylene (TCE), which is also known as trichloroethene, is a synthetic chemical. TCE can be found in soil and water, particularly at hazardous waste sites. The chemical can leach through soil and into groundwater. TCE easily dissolves in water and remains there for a long time. However, because it tends to evaporate easily, it is most commonly found in the vapor form. The maximum containment level for trichloroethene is 5 µg/L.


Uranium is a naturally and commonly occurring radioactive element. Because uranium is found everywhere in small amounts, people always take it into the body from the air, water, food, and soil. In most areas of the United States, low levels of uranium are found in the drinking water. Higher levels may be found in areas with elevated levels of naturally occurring uranium in rocks and soil. The maximum containment level for uranium in drinking water is 30 µg/L.

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