On this page:

• National primary drinking water regulations (NPDWRs)
• List of drinking water contaminants and their maximum contaminant levels (MCLs)
• National secondary drinking water regulations (NSDWRs)
• List of secondary drinking water regulations
• Unregulated drinking water contaminants

National Primary Drinking Water Regulations (NPDWRs)

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.

• EPA’s regulated contaminant timeline
• Visit the Code of Federal Regulations for more information about NPDWRs

List of drinking water contaminants and their maximum contaminant levels (MCLs)

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

• Microorganisms

  Microorganisms

  Contaminant	MCLG1(mg/L)2	MCLor TT1(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	TT3	Gastrointestinal illness (such as diarrhea, vomiting, and cramps)	Human and animal fecal waste
  Giardia lamblia	zero	TT3	Gastrointestinal illness (such as diarrhea, vomiting, and cramps)	Human and animal fecal waste
  Heterotrophic plate count (HPC)	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 (such as 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 (such as diarrhea, vomiting, and cramps)	Human and animal fecal waste

• Disinfection Byproducts

  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 and 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

• Disinfectants

  Disinfectants

  Contaminant	MCLG1(mg/L)2	MCL or TT1(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 (asCl2)	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 and young children: nervous system effects	Water additive used to control microbes

• Inorganic Chemicals

  Inorganic Chemicals

  Contaminant	MCLG1(mg/L)2	MCL or TT1(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	0	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 and electronicsproduction wastes
  Asbestos (fiber > 10 micrometers)	7 million fibers per liter (MFL)	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 distress Long term exposure: Liver or kidney damage People 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 abilities Adults: 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

• Organic Chemicals

  Organic Chemicals

  Contaminant	MCLG1(mg/L)2	MCL or TT1(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

• Radionuclides

  Radionuclides

  Contaminant	MCLG1(mg/L)2	MCL orTT1(mg/L)2	Potential Health Effects from Long-Term Exposure Above theMCL (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 of certain 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/Las 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 (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.)
• Treatment Technique (TT) - 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 (PPM).
• 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 Nephelometric Turbidity Unit (NTU), and samples for turbidity must be less than or equal to 0.3 NTUs 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 NTUs.
    • Heterotrophic Plate Count (HPC): No more than 500 bacterial colonies per milliliter.
    • Long Term 1 Enhanced Surface Water Treatment: Surface water systems or groundwater under the direct influence (GWUDI) systems serving fewer than 10,000 people must comply with the applicable Long Term 1 Enhanced Surface Water Treatment Rule provisions (such as 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 additionalCryptosporidium 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 (TC-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 Maximum Contaminant Level">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 (0.07 mg/L.
  • Haloacetic acids: dichloroacetic acid (zero); trichloroacetic acid (0.02 mg/L); monochloroacetic acid (0.07mg/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 (NSDWRs) 

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.

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Unregulated drinking water contaminants

This list of contaminants which, at the time of publication, are not subject to any proposed or promulgated national primary drinking water regulation (NPDWRs), are known or anticipated to occur in public water systems, and may require regulations under the Safe Drinking Water Act (SDWA).

For more information visit the Drinking Water Contaminant Candidate List (CCL) and Regulatory Determination Website.