Drinking Water Contaminants

EPA  United States Environmental Protection Agency

 National Primary Drinking Water Regulations

National Primary Drinking Water Regulations (NPDWRs or primary standards) are legally enforceable standards that apply to public water systems. Primary standards protect public health by limiting the levels of contaminants in drinking water. Visit the list of regulated contaminants with links for more details.

List of Contaminants & their MCLs

An alphabetical listing with links to fact sheets on the primary drinking water regulations.


Microorganisms
Contaminant MCLG1(mg/L)2 MCL orTT1(mg/L)2 Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term) Sources of Contaminant in Drinking Water
Cryptosporidium zero TT 3 Gastrointestinal illness (e.g., diarrhea, vomiting, cramps) Human and animal fecal waste
Giardia lamblia zero TT3 Gastrointestinal illness (e.g., diarrhea, vomiting, cramps) Human and animal fecal waste
Heterotrophic plate count n/a TT3 HPC has no health effects; it is an analytic method used to measure the variety of bacteria that are common in water. The lower the concentration of bacteria in drinking water, the better maintained the water system is. HPC measures a range of bacteria that are naturally present in the environment
Legionella zero TT3 Legionnaire’s Disease, a type of pneumonia Found naturally in water; multiplies in heating systems
Total Coliforms (including fecal coliform and E. Coli) zero 5.0%4 Not a health threat in itself; it is used to indicate whether other potentially harmful bacteria may be present5 Coliforms are naturally present in the environment; as well as feces; fecal coliforms and E. coli only come from human and animal fecal waste.
Turbidity n/a TT3 Turbidity is a measure of the cloudiness of water. It is used to indicate water quality and filtration effectiveness (e.g., whether disease-causing organisms are present). Higher turbidity levels are often associated with higher levels of disease-causing microorganisms such as viruses, parasites and some bacteria. These organisms can cause symptoms such as nausea, cramps, diarrhea, and associated headaches. Soil runoff
Viruses (enteric) zero TT3 Gastrointestinal illness (e.g., diarrhea, vomiting, cramps) Human and animal fecal waste

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Disinfection Byproducts
Contaminant MCLG1(mg/L)2 MCL orTT1(mg/L)2 Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term) Sources of Contaminant in Drinking Water
Bromate zero 0.010 Increased risk of cancer Byproduct of drinking water disinfection
Chlorite 0.8 1.0 Anemia; infants & young children: nervous system effects Byproduct of drinking water disinfection
Haloacetic acids (HAA5) n/a6 0.0607 Increased risk of cancer Byproduct of drinking water disinfection
Total Trihalomethanes (TTHMs) –> n/a6 –> 0.0807 Liver, kidney or central nervous system problems; increased risk of cancer Byproduct of drinking water disinfection

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Disinfectants
Contaminant MCLG1(mg/L)2 MCL orTT1(mg/L)2 Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term) Sources of Contaminant in Drinking Water
Chloramines (as Cl2) MRDLG=41 MRDL=4.01 Eye/nose irritation; stomach discomfort, anemia Water additive used to control microbes
Chlorine (as Cl2) MRDLG=41 MRDL=4.01 Eye/nose irritation; stomach discomfort Water additive used to control microbes
Chlorine dioxide (as ClO2) MRDLG=0.81 MRDL=0.81 Anemia; infants & young children: nervous system effects Water additive used to control microbes

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Inorganic Chemicals
Contaminant MCLG1(mg/L)2 MCL orTT1(mg/L)2 Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term) Sources of Contaminant in Drinking Water
Antimony 0.006 0.006 Increase in blood cholesterol; decrease in blood sugar Discharge from petroleum refineries; fire retardants; ceramics; electronics; solder
Arsenic 07 0.010 as of 01/23/06 Skin damage or problems with circulatory systems, and may have increased risk of getting cancer Erosion of natural deposits; runoff from orchards, runoff from glass & electronicsproduction wastes
Asbestos (fiber >10 micrometers) 7 million fibers per liter 7 MFL Increased risk of developing benign intestinal polyps Decay of asbestos cement in water mains; erosion of natural deposits
Barium 2 2 Increase in blood pressure Discharge of drilling wastes; discharge from metal refineries; erosion of natural deposits
Beryllium 0.004 0.004 Intestinal lesions Discharge from metal refineries and coal-burning factories; discharge from electrical, aerospace, and defense industries
Cadmium 0.005 0.005 Kidney damage Corrosion of galvanized pipes; erosion of natural deposits; discharge from metal refineries; runoff from waste batteries and paints
Chromium (total) 0.1 0.1 Allergic dermatitis Discharge from steel and pulp mills; erosion of natural deposits
Copper 1.3 TT7; Action Level=1.3 Short term exposure: Gastrointestinal distressLong term exposure: Liver or kidney damagePeople with Wilson’s Disease should consult their personal doctor if the amount of copper in their water exceeds the action level Corrosion of household plumbing systems; erosion of natural deposits
Cyanide (as free cyanide) 0.2 0.2 Nerve damage or thyroid problems Discharge from steel/metal factories; discharge from plastic and fertilizer factories
Fluoride 4.0 4.0 Bone disease (pain and tenderness of the bones); Children may get mottled teeth Water additive which promotes strong teeth; erosion of natural deposits; discharge from fertilizer and aluminum factories
Lead zero TT7; Action Level=0.015 Infants and children: Delays in physical or mental development; children could show slight deficits in attention span and learning abilitiesAdults: Kidney problems; high blood pressure Corrosion of household plumbing systems; erosion of natural deposits
Mercury (inorganic) 0.002 0.002 Kidney damage Erosion of natural deposits; discharge from refineries and factories; runoff from landfills and croplands
Nitrate (measured as Nitrogen) 10 10 Infants below the age of six months who drink water containing nitrate in excess of the MCL could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue-baby syndrome. Runoff from fertilizer use; leaking from septic tanks, sewage; erosion of natural deposits
Nitrite (measured as Nitrogen) 1 1 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. Runoff from fertilizer use; leaking from septic tanks, sewage; erosion of natural deposits
Selenium 0.05 0.05 Hair or fingernail loss; numbness in fingers or toes; circulatory problems Discharge from petroleum refineries; erosion of natural deposits; discharge from mines
Thallium 0.0005 0.002 Hair loss; changes in blood; kidney, intestine, or liver problems Leaching from ore-processing sites; discharge from electronics, glass, and drug factories

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Organic Chemicals
Contaminant MCLG1(mg/L)2 MCL orTT1(mg/L)2 Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term) Sources of Contaminant in Drinking Water
Acrylamide zero TT8

Nervous system or blood problems; increased risk of cancer

Added to water during sewage/wastewater treatment
Alachlor zero 0.002

Eye, liver, kidney or spleen problems; anemia; increased risk of cancer

Runoff from herbicide used on row crops
Atrazine 0.003 0.003

Cardiovascular system or reproductive problems

Runoff from herbicide used on row crops
Benzene zero 0.005

Anemia; decrease in blood platelets; increased risk of cancer

Discharge from factories; leaching from gas storage tanks and landfills
Benzo(a)pyrene (PAHs) zero 0.0002

Reproductive difficulties; increased risk of cancer

Leaching from linings of water storage tanks and distribution lines
Carbofuran 0.04 0.04

Problems with blood, nervous system, or reproductive system

Leaching of soil fumigant used on rice and alfalfa
Carbon tetrachloride zero 0.005

Liver problems; increased risk of cancer

Discharge from chemical plants and other industrial activities
Chlordane zero 0.002

Liver or nervous system problems; increased risk of cancer

Residue of banned termiticide
Chlorobenzene 0.1 0.1

Liver or kidney problems

Discharge from chemical and agricultural chemical factories
2,4-D 0.07 0.07

Kidney, liver, or adrenal gland problems

Runoff from herbicide used on row crops
Dalapon 0.2 0.2

Minor kidney changes

Runoff from herbicide used on rights of way
1,2-Dibromo-3-chloropropane (DBCP) zero 0.0002

Reproductive difficulties; increased risk of cancer

Runoff/leaching from soil fumigant used on soybeans, cotton, pineapples, and orchards
o-Dichlorobenzene 0.6 0.6

Liver, kidney, or circulatory system problems

Discharge from industrial chemical factories
p-Dichlorobenzene 0.075 0.075

Anemia; liver, kidney or spleen damage; changes in blood

Discharge from industrial chemical factories
1,2-Dichloroethane zero 0.005

Increased risk of cancer

Discharge from industrial chemical factories
1,1-Dichloroethylene 0.007 0.007

Liver problems

Discharge from industrial chemical factories
cis-1,2-Dichloroethylene 0.07 0.07

Liver problems

Discharge from industrial chemical factories
trans-1,2-Dichloroethylene 0.1 0.1

Liver problems

Discharge from industrial chemical factories
Dichloromethane zero 0.005

Liver problems; increased risk of cancer

Discharge from drug and chemical factories
1,2-Dichloropropane zero 0.005

Increased risk of cancer

Discharge from industrial chemical factories
Di(2-ethylhexyl) adipate 0.4 0.4

Weight loss, liver problems, or possible reproductive difficulties.

Discharge from chemical factories
Di(2-ethylhexyl) phthalate zero 0.006

Reproductive difficulties; liver problems; increased risk of cancer

Discharge from rubber and chemical factories
Dinoseb 0.007 0.007

Reproductive difficulties

Runoff from herbicide used on soybeans and vegetables
Dioxin (2,3,7,8-TCDD) zero 0.00000003

Reproductive difficulties; increased risk of cancer

Emissions from waste incineration and other combustion; discharge from chemical factories
Diquat 0.02 0.02

Cataracts

Runoff from herbicide use
Endothall 0.1 0.1

Stomach and intestinal problems

Runoff from herbicide use
Endrin 0.002 0.002

Liver problems

Residue of banned insecticide
Epichlorohydrin zero TT8

Increased cancer risk, and over a long period of time, stomach problems

Discharge from industrial chemical factories; an impurity of some water treatment chemicals
Ethylbenzene 0.7 0.7

Liver or kidneys problems

Discharge from petroleum refineries
Ethylene dibromide zero 0.00005

Problems with liver, stomach, reproductive system, or kidneys; increased risk of cancer

Discharge from petroleum refineries
Glyphosate 0.7 0.7

Kidney problems; reproductive difficulties

Runoff from herbicide use
Heptachlor zero 0.0004

Liver damage; increased risk of cancer

Residue of banned termiticide
Heptachlor epoxide zero 0.0002

Liver damage; increased risk of cancer

Breakdown of heptachlor
Hexachlorobenzene zero 0.001

Liver or kidney problems; reproductive difficulties; increased risk of cancer

Discharge from metal refineries and agricultural chemical factories
Hexachlorocyclopentadiene 0.05 0.05

Kidney or stomach problems

Discharge from chemical factories
Lindane 0.0002 0.0002

Liver or kidney problems

Runoff/leaching from insecticide used on cattle, lumber, gardens
Methoxychlor 0.04 0.04

Reproductive difficulties

Runoff/leaching from insecticide used on fruits, vegetables, alfalfa, livestock
Oxamyl (Vydate) 0.2 0.2

Slight nervous system effects

Runoff/leaching from insecticide used on apples, potatoes, and tomatoes
Polychlorinated biphenyls (PCBs) zero 0.0005

Skin changes; thymus gland problems; immune deficiencies; reproductive or nervous system difficulties; increased risk of cancer

Runoff from landfills; discharge of waste chemicals
Pentachlorophenol zero 0.001

Liver or kidney problems; increased cancer risk

Discharge from wood preserving factories
Picloram 0.5 0.5

Liver problems

Herbicide runoff
Simazine 0.004 0.004

Problems with blood

Herbicide runoff
Styrene 0.1 0.1

Liver, kidney, or circulatory system problems

Discharge from rubber and plastic factories; leaching from landfills
Tetrachloroethylene zero 0.005

Liver problems; increased risk of cancer

Discharge from factories and dry cleaners
Toluene 1 1

Nervous system, kidney, or liver problems

Discharge from petroleum factories
Toxaphene zero 0.003

Kidney, liver, or thyroid problems; increased risk of cancer

Runoff/leaching from insecticide used on cotton and cattle
2,4,5-TP (Silvex) 0.05 0.05

Liver problems

Residue of banned herbicide
1,2,4-Trichlorobenzene 0.07 0.07

Changes in adrenal glands

Discharge from textile finishing factories
1,1,1-Trichloroethane 0.20 0.2

Liver, nervous system, or circulatory problems

Discharge from metal degreasing sites and other factories
1,1,2-Trichloroethane 0.003 0.005

Liver, kidney, or immune system problems

Discharge from industrial chemical factories
Trichloroethylene zero 0.005

Liver problems; increased risk of cancer

Discharge from metal degreasing sites and other factories
Vinyl chloride zero 0.002

Increased risk of cancer

Leaching from PVC pipes; discharge from plastic factories
Xylenes (total) 10 10

Nervous system damage

Discharge from petroleum factories; discharge from chemical factories

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Radionuclides
Contaminant MCLG1(mg/L)2 MCL orTT1(mg/L)2 Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term) Sources of Contaminant in Drinking Water
Alpha particles none7 ———- zero 15 picocuries per Liter (pCi/L) Increased risk of cancer Erosion of natural deposits of certain minerals that are radioactive and may emit a form of radiation known as alpha radiation
Beta particles and photon emitters
none7 ———- zero 4 millirems per year Increased risk of cancer Decay of natural and man-made deposits ofcertain minerals that are radioactive and may emit forms of radiation known as photons and beta radiation
Radium 226 and Radium 228 (combined) none7 ———- zero 5 pCi/L Increased risk of cancer Erosion of natural deposits
Uranium zero 30 ug/L as of 12/08/03 Increased risk of cancer, kidney toxicity Erosion of natural deposits

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Notes

1 Definitions: Maximum Contaminant Level Goal (MCLG) – The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable public health goals. Maximum Contaminant Level (MCL) – The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards. Maximum Residual Disinfectant Level Goal (MRDLG) – The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants. (TT) Treatment Technique – A required process intended to reduce the level of a contaminant in drinking water. Maximum Residual Disinfectant Level (MRDL) – The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.

2 Units are in milligrams per liter (mg/L) unless otherwise noted. Milligrams per liter are equivalent to parts per million.

3 EPA’s surface water treatment rules require systems using surface water or ground water under the direct influence of surface water to (1) disinfect their water, and (2) filter their water or meet criteria for avoiding filtration so that the following contaminants are controlled at the following levels:

  • Cryptosporidium: Unfiltered systems are required to include Cryptosporidium in their existing watershed control provisions.
  • Giardia lamblia: 99.9% removal/inactivation
  • Viruses: 99.99% removal/inactivation
  • Legionella: No limit, but EPA believes that if Giardia and viruses are removed/inactivated, according to the treatment techniques in the Surface Water Treatment Rule, Legionella will also be controlled.
  • Turbidity: For systems that use conventional or direct filtration, at no time can turbidity (cloudiness of water) go higher than 1 nephelolometric turbidity unit NTU), and samples for turbidity must be less than or equal to 0.3 NTU in at least 95 percent of the samples in any month. Systems that use filtration other than the conventional or direct filtration must follow state limits, which must include turbidity at no time exceeding 5 NTU.
  • HPC: No more than 500 bacterial colonies per milliliter.
  • Long Term 1 Enhanced Surface Water Treatment: Surface water systems or (GWUDI) systems serving fewer than 10,000 people must comply with the applicable Long Term 1 Enhanced Surface Water Treatment Rule provisions (e.g. turbidity standards, individual filter monitoring, Cryptosporidium removal requirements, updated watershed control requirements for unfiltered systems).
  • Long Term 2 Enhanced Surface Water Treatment Rule This rule applies to all surface water systems or ground water systems under the direct influence of surface water. The rule targets additional Cryptosporidium treatment requirements for higher risk systems and includes provisions to reduce risks from uncovered finished water storage facilities and to ensure that the systems maintain microbial protection as they take steps to reduce the formation of disinfection byproducts.
  • Filter Backwash Recycling; The Filter Backwash Recycling Rule requires systems that recycle to return specific recycle flows through all processes of the system’s existing conventional or direct filtration system or at an alternate location approved by the state.

4 No more than 5.0% samples total coliform-positive in a month. (For water systems that collect fewer than 40 routine samples per month, no more than one sample can be total coliform-positive per month.) Every sample that has total coliform must be analyzed for either fecal coliforms or E. coli if two consecutive TC-positive samples, and one is also positive for E.coli fecal coliforms, system has an acute MCL violation.

5 Fecal coliform and E. coli are bacteria whose presence indicates that the water may be contaminated with human or animal wastes. Disease-causing microbes (pathogens) in these wastes can cause diarrhea, cramps, nausea, headaches, or other symptoms. These pathogens may pose a special health risk for infants, young children, and people with severely compromised immune systems.

6 Although there is no collective MCLG for this contaminant group, there are individual MCLGs for some of the individual contaminants:

  • Trihalomethanes: bromodichloromethane (zero); bromoform (zero); dibromochloromethane (0.06 mg/L): chloroform (0.07mg/L).
  • Haloacetic acids: dichloroacetic acid (zero); trichloroacetic acid (0.02 mg/L); monochloroacetic acid (0.07 mg/L). Bromoacetic acid and dibromoacetic acid are regulated with this group but have no MCLGs.

7 Lead and copper are regulated by a Treatment Technique that requires systems to control the corrosiveness of their water. If more than 10% of tap water samples exceed the action level, water systems must take additional steps. For copper, the action level is 1.3 mg/L, and for lead is 0.015 mg/L.

8 Each water system must certify, in writing, to the state (using third-party or manufacturer’s certification) that when acrylamide and epichlorohydrin are used to treat water, the combination (or product) of dose and monomer level does not exceed the levels specified, as follows:

  • Acrylamide = 0.05% dosed at 1 mg/L (or equivalent)
  • Epichlorohydrin = 0.01% dosed at 20 mg/L (or equivalent)

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National Secondary Drinking Water Regulations

National Secondary Drinking Water Regulations (NSDWRs or secondary standards) are non-enforceable guidelines regulating contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor, or color) in drinking water. EPA recommends secondary standards to water systems but does not require systems to comply. However, states may choose to adopt them as enforceable standards.

List of National Secondary Drinking Water Regulations
Contaminant Secondary Standard
Aluminum 0.05 to 0.2 mg/L
Chloride 250 mg/L
Color 15 (color units)
Copper 1.0 mg/L
Corrosivity noncorrosive
Fluoride 2.0 mg/L
Foaming Agents 0.5 mg/L
Iron 0.3 mg/L
Manganese 0.05 mg/L
Odor 3 threshold odor number
pH 6.5-8.5
Silver 0.10 mg/L
Sulfate 250 mg/L
Total Dissolved Solids 500 mg/L
Zinc 5 mg/L

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Unregulated Contaminants

This list of contaminants which, at the time of publication, are not subject to any proposed or promulgated national primary drinking water regulation (NPDWR), are known or anticipated to occur in public water systems, and may require regulations under SDWA. For more information check out the list, or vist the Drinking Water Contaminant Candidate List (CCL) web site.

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