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Private Well 101: Drinking Water Standards

Yilin Zhuang, Andrea Albertin, and Arthur G. Hornsby

Introduction

Drinking water comes from a variety of sources, including public water systems, private wells, or bottled water. While public water systems are monitored under the federal Safe Drinking Water Act, private wells are not regulated (US Environmental Protection Agency 2004). Private well users are responsible for the management and protection of their wells and water quality.

This EDIS publication is for Florida homeowners who are interested in learning more about drinking water standards. It also serves as a reference for well owners to understand their drinking water quality.

Primary Drinking Water Standards

Drinking water supplied by municipal water systems is monitored for many contaminants. As authorized by the 1974 Safe Drinking Water Act and its amendments, the US Environmental Protection Agency (EPA) has established limits on the concentration of certain drinking water contaminants allowed in public water supplies. These limits are set to protect your health and ensure that your water is of good quality. The Florida Department of Environmental Protection (FDEP) has accepted the National Standards as published herein.

The EPA standards for drinking water fall into two categories: Primary Standards and Secondary Standards. Primary Standards are based on health considerations and are enforced by the EPA. They protect you from three classes of toxic pollutants:

  • Pathogens: Disease-causing organisms such as bacteria, fungi, or viruses.
  • Radioactive elements: Substances that emit radiation, such as radium, uranium, and plutonium. Radiation can cause cancer in people and other living things.
  • Toxic chemicals: Substances that can injure or kill people.

Additionally, the Primary Standards establish a limit, called the Maximum Contaminant Level (MCL), on the highest allowable concentration of a contaminant in drinking water supplied by municipal water systems. The MCL is usually expressed in milligrams per liter (mg/L). Table 1-1 to Table 1-6 contain the current primary drinking water standards.

How Primary Standards Are Set

EPA regulators develop Primary Standards for drinking water contaminants based on three criteria:

  • The contaminant causes adverse health effects.
  • It is detectable in drinking water.
  • It is known to occur in drinking water.

When establishing Primary Standards for a drinking water contaminant, the government first looks at all the toxicological data on that contaminant, usually obtained from acute and chronic animal studies. Occasionally human clinical or epidemiological data are also available. Experts use this information to estimate the concentration of a drinking water contaminant that may be toxic and the concentrations, if any, that may cause no adverse effects. Because the levels of contaminants found in drinking water are rarely high enough to cause acute health effects, health officials are most concerned about chronic health effects such as cancer, birth defects, miscarriages, nervous system disorders, and organ damages. These health effects may occur after prolonged exposure to small amounts of a substance.

If the EPA decides not to regulate a contaminant based on the above three criteria, they may decide to develop a health advisory. A health advisory is a nonenforceable federal limit. It serves as technical guidance for federal, state, and local officials.

Regulators treat cancer-causing substances (carcinogens) differently from contaminants that cause other health effects.

Noncancerous Chemicals

For chemicals that cause adverse health effects other than cancer, Acceptable Daily Intake (ADI) levels are determined. ADI is the daily dose of a substance that a person can ingest over a lifetime without harming their health. The ADI level also includes a conservative safety margin. Regulators use the ADI to establish a Maximum Contaminant Level Goal (MCLG). The MCLG is the concentration of a contaminant that experts believe a person can drink safely over their lifetime. It is based entirely on health considerations and, as a health goal, is set at a level where no adverse health effects should occur. The MCLG is not enforced by the EPA. It is used to set enforceable drinking water standards, the Maximum Contaminant Level (MCL). The MCL is the Primary Standard measurement enforced by the EPA. It is set as close as possible to the MCLG. When setting the MCL, EPA regulators consider the feasibility and the combined cost of analyzing water for a contaminant and for treating water to remove the contaminant in addition to public health considerations. Therefore, the MCL is often less stringent than the MCLG.

Cancerous Chemicals

When establishing primary standards for chemicals that are believed to cause cancer, no concentration is considered safe. Therefore, the lifetime goal, the MCLG, is set at zero. However, a zero level is not always feasible to achieve. For example, laboratories may not be able to detect carcinogens found at low levels, or the cost of maintaining the levels of carcinogens below the MCL may not be feasible. In addition, when carcinogens are found at very low concentrations, the risk of cancer becomes so small that it is considered negligible. Therefore, regulators must decide what level of risk is acceptable. It may be one excess cancer in 10,000 persons or one excess cancer in 1 million persons exposed over a lifetime of 70 years. The concentration of chemical estimated to cause this "acceptable level" of risk is called the Risk Estimate. It is then used to set the MCL.

Table 1-1 to Table 1-6 list the current primary drinking water standards for different categories of contaminants: microorganisms, disinfection byproducts, disinfectants, inorganic chemicals, organic chemicals, and radionuclides.

Secondary Drinking Water Standards

Secondary Standards regulate contaminants that cause offensive taste, odor, color, corrosivity, foaming, and staining in drinking water. The concentration limit is called the Secondary Maximum Contaminant Level (SMCL). Secondary Standards are not enforced because they are not considered to pose a risk to human health at the recommended SMCL. They are guidelines for water treatment plant operators and state governments attempting to provide communities with the best quality water possible. Table 2 lists the current secondary drinking water standards.

Drinking Water Standards Are Not Absolute

Drinking water standards do reflect sound scientific judgment and are based on the best and most current knowledge available. They also include margins of safety to reduce adverse health effects and protect human health. The Safe Drinking Water Act also requires EPA to review each national primary drinking water regulation at least once every six years and revise them, if appropriate. As part of the "Six-Year Review," EPA evaluates any newly available data, information, and technologies to determine if any regulatory revisions are needed. Revisions must maintain or strengthen public health protection.

However, it is also important to understand that Primary Standards for drinking water contaminants do not guarantee that water with a contaminant level below the standard is risk-free, nor do they mean that water with a higher level is unsafe. It is mainly because setting drinking water standards is an imperfect process:

  • Regulatory decisions are often complicated by economic, political, and social considerations.
  • Data relating human health effects to chemicals in drinking water are limited, and scientists have difficulty predicting the effects of drinking small amounts of chemicals for many years.
  • The standards do not take into account the possible presence of other chemicals, which may increase or decrease the toxicity of the contaminant.

Current Drinking Water Standards

As mentioned earlier, the EPA has set MCLs for microorganisms, disinfection byproducts, disinfectants, inorganic chemicals, organic chemicals, and radionuclides. The EPA periodically issues standards for additional organic and inorganic chemicals, microbes, and viruses. Many more organic chemicals known to be present in drinking water are not currently regulated by either state or federal standards.

Working through state governments, the EPA monitors community drinking water. When a standard is exceeded, the EPA requires that contaminant level to be reduced to the MCL. The corrective treatment is left to the individual water system, usually a private utility.

State Responsibilities

Ultimately, regulatory officials in your state set and enforce drinking water standards for EPA-regulated contaminants and for other contaminants. However, states are not permitted to set standards that are less stringent than the MCLs set by the EPA.

Drinking water standards represent conservative judgements of scientists and regulators and are based on all available information on the health effects of drinking water contaminants. Although current drinking water standards do not guarantee that the glass of water you draw from your tap will be absolutely safe and pure, they do reflect sound scientific judgment and are based on all the knowledge that is available.

Private Well Owner Responsibility

As a private well owner, you are responsible for the quality of your own drinking water. Private wells are usually not required to test their drinking water to meet primary drinking water standards. However, you can use the public drinking water standards as guidelines when evaluating the quality of your drinking water.

For more information about drinking water standards, please see US EPA, “Drinking Water Requirements for States and Public Water Systems”: https://www.epa.gov/dwreginfo.

Publication History

Stewart, Judith C., Ann T. Lemley, Sharon I. Hogan, and Richard A. Weismiller. 1989. “Health Effects of Drinking Water Contaminants.” Cornell University and University of Maryland.

Stewart, Judith C., Ann T. Lemley, Sharon I. Hogan, Richard A. Weismiller, and Arthur G. Hornsby. 2001. “Drinking Water Standards.” University of Florida Institute Food and Agricultural Sciences.

References

US Environmental Protection Agency. 2004. “Understanding the Safe Drinking Water Act.” https://www.epa.gov/sites/production/files/2015-04/documents/epa816f04030.pdf

US Environmental Protection Agency. January 26, 2022. “National Primary Drinking Water Regulations.” https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#six

US Environmental Protection Agency. February 17, 2022. “Secondary Drinking Water Standards: Guidance for Nuisance Chemicals.” https://www.epa.gov/sdwa/secondary-drinking-water-standards-guidance-nuisance-chemicals

Table 1-1. US EPA Primary Drinking Water Standards—Microorganisms.

Contaminant

MCLG1

(mg/L)

MCL2 or TT3 (mg/L)

Potential Health Effects from Long-Term Exposure above the MCL (unless specified as short-term)

Sources of Contaminant in Drinking Water

Cryptosporidium

zero

TT

Gastrointestinal illness (such as diarrhea, vomiting, and cramps)

Human and animal fecal waste

Giardia lamblia

zero

TT

Gastrointestinal illness (such as diarrhea, vomiting, and cramps)

Human and animal fecal waste

Heterotrophic plate count (HPC)

n/a

TT

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

TT

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%

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

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

TT

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

TT

Gastrointestinal illness (such as diarrhea, vomiting, and cramps)

Human and animal fecal waste

1 MCLG—Maximum Contaminant Level Goal: 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 nonenforceable public health goals.

2 MCL—Maximum Contaminant Level: 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.

3 TT—Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water.

4 For the latest primary drinking water standards in microorganisms, please visit the US EPA National Primary Drinking Water Regulations website: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#Microorganisms.

Table 1-2. US EPA Primary Drinking Water Standards—Disinfection Byproducts.

Contaminant

MCLG1

(mg/L)

MCL2 or TT3

(mg/L)

Potential Health Effects from Long-Term Exposure above the MCL (unless specified as short-term)

Sources of Contaminant in Drinking Water

Bromate

zero

0.01

Increased risk of cancer

Byproduct of drinking water disinfection

Chlorite

0.8

1

Anemia; infants and young children: nervous system effects

Byproduct of drinking water disinfection

Haloacetic acids (HAA5)

n/a

0.06

Increased risk of cancer

Byproduct of drinking water disinfection

Total trihalomethanes (TTHMs)

n/a

0.08

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

Byproduct of drinking water disinfection

1 MCLG—Maximum Contaminant Level Goal: 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 nonenforceable public health goals.

2 MCL—Maximum Contaminant Level: 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.

3 TT—Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water.

4 For the latest primary drinking water standards in disinfection byproducts, please visit the US EPA National Primary Drinking Water Regulations website: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#Byproducts.

 

Table 1-3. US EPA Primary Drinking Water Standards—Disinfectants.

Contaminant

MCLG1

(mg/L)

MCL2 or TT3

(mg/L)

Potential Health Effects from Long-Term Exposure above the MCL (unless specified as short-term)

Sources of Contaminant in Drinking Water

Chloramines (as Cl2)

41

4.01

Eye/nose irritation; stomach discomfort, anemia

Water additive used to control microbes

Chlorine (as Cl2)

41

4.01

Eye/nose irritation; stomach discomfort

Water additive used to control microbes

Chlorine dioxide (as ClO2)

0.81

0.81

Anemia; infants and young children: nervous system effects

Water additive used to control microbes

1 MCLG—Maximum Contaminant Level Goal: 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 nonenforceable public health goals.

2 MCL—Maximum Contaminant Level: 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.

3 TT—Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water.

4 For the latest primary drinking water standards in disinfectants, please visit US EPA National Primary Drinking Water Regulations website: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#Disinfectants.

 

Table 1-4. US EPA Primary Drinking Water Standards—Inorganic Chemicals.

Contaminant

MCLG1

(mg/L)

MCL2 or TT3

(mg/L)

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

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 electronics production 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

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

4

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

Water additive that promotes strong teeth; erosion of natural deposits; discharge from fertilizer and aluminum factories

Lead

zero

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

1 MCLG—Maximum Contaminant Level Goal: 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 nonenforceable public health goals.

2 MCL—Maximum Contaminant Level: 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.

3 TT—Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water.

4 For the latest primary drinking water standards in inorganic chemicals, please visit the US EPA National Primary Drinking Water Regulations website: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#Inorganic.

Table 1-5.US EPA Primary Drinking Water Standards—Organic Chemicals.

Contaminant

MCLG1

(mg/L)

MCL2 or TT3 (mg/L)

Potential Health Effects from Long-Term Exposure above the MCL (unless specified as short-term)

Sources of Contaminant in Drinking Water

Acrylamide

zero

TT

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

3E-08

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

0.2

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

1 MCLG—Maximum Contaminant Level Goal: 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 nonenforceable public health goals.

2 MCL—Maximum Contaminant Level: 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.

3 TT—Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water.

4 For the latest primary drinking water standards in organic chemicals, please visit the US EPA National Primary Drinking Water Regulations website: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#Organic.

 

Table 1-6. US EPA Primary Drinking Water Standards—Radionuclides.

Contaminant

MCLG1

(mg/L)

MCL2 or TT3

(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

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

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)

zero

5 pCi/L

Increased risk of cancer

Erosion of natural deposits

Uranium

zero

30 ug/L

Increased risk of cancer, kidney toxicity

Erosion of natural deposits

1 MCLG—Maximum Contaminant Level Goal: 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 nonenforceable public health goals.

2 MCL—Maximum Contaminant Level: 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.

3 TT—Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water.

4 For the latest primary drinking water standards in radionuclides, please visit the US EPA National Primary Drinking Water Regulations website: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#Radionuclides.

 

Table 2. US EPA Secondary Drinking Water Standards.

Contaminant

Secondary MCL

Noticeable Effects above the Secondary MCL

Aluminum

0.05 to 0.2 mg/L

colored water

Chloride

250 mg/L

salty taste

Color

15 color units

visible tint

Copper

1.0 mg/L

metallic taste; blue-green staining

Corrosivity

Noncorrosive

metallic taste; corroded pipes/ fixtures staining

Fluoride

2.0 mg/L

tooth discoloration

Foaming agents

0.5 mg/L

frothy, cloudy; bitter taste; odor

Iron

0.3 mg/L

rusty color; sediment; metallic taste; reddish or orange staining

Manganese

0.05 mg/L

black to brown color; black staining; bitter metallic taste

Odor

3 TON (threshold odor number)

"rotten-egg," musty or chemical smell

pH

6.5–8.5

low pH: bitter metallic taste; corrosion

 

 

high pH: slippery feel; soda taste; deposits

Silver

0.1 mg/L

skin discoloration; graying of the white part of the eye

Sulfate

250 mg/L

salty taste

Total Dissolved Solids (TDS)

500 mg/L

hardness; deposits; colored water; staining; salty taste

Zinc

5 mg/L

metallic taste

1 For the latest second drinking water standards, please visit the US EPA Secondary Drinking Water Standards: Guidance for Nuisance Chemicals website: https://www.epa.gov/sdwa/secondary-drinking-water-standards-guidance-nuisance-chemicals#table.

 

Peer Reviewed

Publication #SL159

Release Date:June 30th, 2022

Related Experts

Albertin, Andrea R.

Specialist/SSA/RSA

University of Florida

Zhuang, Yilin

Specialist/SSA/RSA

University of Florida

Fact Sheet

About this Publication

This document is SL159, one of a series of the Department of Soil, Water, and Ecosystem Sciences, UF/IFAS Extension. Original publication date February 2001. Revised June 2022. Visit the EDIS website at https://edis.ifas.ufl.edu for the currently supported version of this publication.

About the Authors

Yilin Zhuang, regional specialized agent II, UF/IFAS Extension Central District; Andrea Albertin, regional specialized agent and Extension agent II, UF/IFAS Extension Northwest District; and Arthur G. Hornsby, professor emeritus (deceased), UF/IFAS Department of Soil, Water, and Ecosystem Sciences; UF/IFAS Extension, Gainesville, FL 32611.

Contacts

  • Yilin Zhuang