Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

Congressional research reportSep 10, 2024

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Regulating Contaminants

Under the Safe Drinking Water Act (SDWA)

Updated September 10, 2024

Congressional Research Service

https://crsreports.congress.gov

R46652

SUMMARY

Regulating Contaminants

Under the Safe Drinking Water Act (SDWA)

Detections of contaminants in public water supplies in numerous states have raised questions

about drinking water quality and have increased congressional interest in the Environmental

Protection Agency’s (EPA’s) efforts to regulate contaminants under the Safe Drinking Water Act

(SDWA). Congress is particularly interested in the EPA’s process for evaluating new

contaminants for potential regulation. Detections of already-regulated contaminants, such as lead,

have also raised concerns about the effectiveness of certain existing regulations.

R46652

September 10, 2024

Elena H. Humphreys

Analyst in Environmental

Policy

SDWA is the key federal law that authorizes EPA to promulgate regulations to control contaminants in public water supplies.

Since its enactment in 1974, EPA has issued drinking water regulations for 100 contaminants. Congress has twice revised the

act’s process for evaluating contaminants and developing drinking water regulations (in 1986 and 1996). In 1986, Congress

directed EPA to develop regulations for 83 contaminants within 3 years, and adopt regulations, every 3 years, for at least 25

new contaminants. In 1996, when this regulatory schedule proved unworkable, Congress amended SDWA to establish a riskbased process that prioritizes contaminants for regulation based on health effects and occurrence.

Under SDWA, EPA follows a multistep process to evaluate and prioritize contaminants for regulation. This process includes

identifying contaminants of potential concern, assessing health risks, collecting national occurrence data (and developing

reliable and field-tested analytical methods necessary to do so), and making determinations as to whether a contaminant

warrants regulation. Since 1996, EPA has considered over 7,500 contaminants for potential regulation, revised existing

regulations, and established new regulations and standards for several contaminants.

When EPA determines that a contaminant warrants regulation, SDWA directs EPA to propose a “national primary drinking

water regulation” and request public comment within 24 months. Within 18 months of the proposal, EPA is required to

promulgate a final rule. EPA is required to establish a nonenforceable maximum contaminant level goal (MCLG) at a level at

which no known or anticipated adverse health effects occur and allowing for an adequate margin of safety. Drinking water

regulations generally specify a maximum contaminant level (MCL)—an enforceable limit for a contaminant in public water

supplies. SDWA requires EPA to set the MCL as close to the MCLG as “feasible,” taking treatment efficacy and costs into

consideration. Concurrent with proposing a regulation, SDWA requires EPA to publish a “health risk reduction and cost

analysis” for each contaminant covered by the proposed regulation and make a determination whether or not the benefits of

regulation outweigh the compliance costs.

EPA’s regulations generally take effect three years after promulgation, though the agency may allow up to two additional

years, under certain conditions. For each drinking water regulation, SDWA requires EPA to identify a list of best available

technologies, treatment techniques, and other means that EPA finds feasible for meeting the MCL. In addition, EPA is

required to identify treatment technologies that achieve the MCL and are affordable for small systems. Each regulation also

establishes associated monitoring and reporting requirements. SDWA requires EPA to review—and, if necessary, revise—

each existing national primary drinking water regulation every six years. SDWA also requires that any revisions to drinking

water regulations maintain or provide greater health protection.

Under the current SDWA statutory framework, evaluating and developing regulations for contaminants requires data,

including data from peer-reviewed scientific studies on potential health effects and nationally representative occurrence data.

For some contaminants, the availability or development of (1) data, (2) analytical methods to detect contaminants in drinking

water, and (3) treatment technologies pose technical and resource challenges.

Congressional attention has centered on EPA’s implementation of SDWA regulatory development provisions. Some

stakeholders also have raised concerns about regulatory costs for communities. In recent Congresses, some Members have

raised concerns that the act’s process is lengthy and complicated and does not allow for the timely regulation of contaminants

of concern in drinking water. Others have expressed concern that proposals to expedite regulation by removing elements of

SDWA regulatory development provisions (e.g., the requirement to use peer-reviewed science or a health-risk-based

approach) may result in increased costs to communities without commensurate public health protection. This debate was

heightened prior to EPA’s determination to regulate per- and polyfluoroalkyl substances (PFAS) in 2021, yet stakeholders

raised similar concerns after EPA’s 2024 finalization of a regulation for six PFAS.

Congressional Research Service

Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

Contents

Introduction ..................................................................................................................................... 1

History of SDWA Section 1412 “National Drinking Water Regulations” ....................................... 2

Regulated Public Water Systems ..................................................................................................... 5

Regulating Contaminants in Public Water Supplies ........................................................................ 6

Identifying Contaminants for Consideration ............................................................................. 6

Evaluating Contaminant Occurrence ........................................................................................ 8

Determining Whether or Not to Regulate ................................................................................. 9

Regulatory Determination Cycles ..................................................................................... 10

Promulgating a Drinking Water Regulation ............................................................................ 12

Maximum Contaminant Level Goals ................................................................................ 13

Feasibility and Maximum Contaminant Levels ................................................................ 14

Additional Health Risk Reduction and Cost Considerations ............................................ 15

Health Risk Reduction Cost Analysis ............................................................................... 15

Variances and Exemptions ...................................................................................................... 17

Six-Year Reviews .................................................................................................................... 18

Considerations for Regulatory Determinations ............................................................................. 20

Data Availability and Quality .................................................................................................. 20

Availability of Analytical Methods and Laboratory Capacity ................................................. 21

Congressional Interest ................................................................................................................... 22

Figures

Figure 1. Simplified Process for Regulating Contaminants Under SDWA ................................... 13

Tables

Table 1. SDWA Contaminant Regulation Timeline ......................................................................... 4

Table 2. Public Water System Statistics .......................................................................................... 6

Table 3. EPA’s Drinking Water Contaminant Regulatory Development Actions .......................... 19

Table A-1. Contaminant Candidate Lists (CCLs) .......................................................................... 25

Table B-1. Unregulated Contaminant Monitoring Rules (UCMRs) .............................................. 26

Table C-1. Regulatory Determinations (RDs) ............................................................................... 27

Appendixes

Appendix A. Contaminant Candidate Lists ................................................................................... 25

Appendix B. Unregulated Contaminant Monitoring Rules ........................................................... 26

Appendix C. Regulatory Determinations ...................................................................................... 27

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Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

Contacts

Author Information........................................................................................................................ 28

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Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

Introduction

Detections of contaminants in public water supplies have raised questions about the quality of

drinking water and have increased congressional interest in the Environmental Protection

Agency’s (EPA’s) efforts to regulate contaminants under the Safe Drinking Water Act (SDWA).

Congress enacted SDWA in 1974 to address the quality of public drinking water supplies and

protect public health.1 A key part of the act is the authority for EPA to regulate contaminants in

public water supplies. Since enactment, Congress has revised the act’s process for contaminant

regulation twice, in 1986 and in 1996. The 1996 amendments established specific contaminant

identification, assessment, and regulatory determination processes for the purpose of focusing

regulatory resources and requirements toward contaminants of greatest public health concern.

Since 1996, EPA has updated several drinking water regulations, promulgated regulations for

additional contaminants under other SDWA authorities, and evaluated more than 7,500

contaminants for potential regulation. In April 2024, EPA finalized a national primary drinking

water regulation (NPDWR) for six per- and polyfluoroalkyl substances (PFAS).2

SDWA requires EPA to use the best available, peer-reviewed science to characterize a

contaminant’s health effects and occurrence in water supplies to determine whether a contaminant

warrants national regulation. EPA has long recognized that limited data on unregulated

contaminants of concern has hindered the agency’s ability to make regulatory determinations.3 In

a 2011 report, the U.S. Government Accountability Office (GAO) made a similar finding.4 EPA’s

efforts to develop peer-reviewed science necessary to support regulatory determinations for

unregulated contaminants—or to update existing contaminant regulations—have been affected by

data availability and available agency resources, among other factors.

This report discusses the SDWA provisions relevant to how EPA evaluates contaminants to

determine whether a contaminant warrants an NPDWR. It also provides an overview of the

regulatory development process, and analyzes certain issues that may affect implementation of

SDWA regulatory development provisions. Regarding specific SDWA drinking water regulations,

some have raised concerns over how the agency calculates costs when developing drinking water

standards. For individual contaminants, costs vary and involve specific considerations, as does

the ability of water systems to afford such costs. This report does not discuss EPA’s calculation of

costs for each regulation.

In addition to the agency’s work related to contaminant regulation, EPA has issued other SDWA

regulations applicable to public water systems. These include regulations to reduce lead content

in drinking water pipes and plumbing and to increase consumer information and public

notification about drinking water quality and compliance.5 The report is primarily limited to

1 Safe Drinking Water Act of 1974 (P.L. 93-523), enacted December 16, 1974.

2 U.S. Environmental Protection Agency (EPA), “PFAS National Primary Drinking Water Regulation,” 89 Federal

3 See, for example, Table 2, “Information Gaps for the CCL 2 Chemical Contaminants,” EPA, “Drinking Water:

Regulatory Determinations Regarding Contaminants on the Second Drinking Water Contaminant Candidate List,” 73

Federal Register 44251-44261, July 30, 2008.

4 U.S. Government Accountability Office (GAO), EPA Should Improve Implementation of Requirements on Whether to

Regulate Additional Contaminants, 11-254, May 27, 2011, at https://www.gao.gov/products/GAO-11-254.

5 Other regulations include the “Use of Lead Free Pipes, Fittings, Fixtures, Solder, and Flux for Drinking Water” rule

(85 Federal Register 54235-54259) and “right-to-know” rules (e.g., public notification rule [65 Federal Register

25982-26049] and consumer confidence report rule [63 Federal Register 44512-44536]).

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EPA’s implementation of the process outlined in SDWA Section 1412 “National Drinking Water

Regulations” for evaluating contaminants for regulation.6

History of SDWA Section 1412 “National Drinking

Water Regulations”

The Safe Drinking Water Act of 1974 established the federal role in regulating contaminants in

public water supplies. The 1974 act directed EPA to promulgate “national interim primary

drinking water regulations,” with enforceable standards (i.e., maximum contaminant levels), for a

list of contaminants based on the 1962 U.S. Public Health Service interstate carrier drinking water

quality standards.7 It also directed the National Academy of Sciences to conduct a study and

recommend maximum contaminant levels to protect human health. EPA was required to set the

interim regulations’ revised levels as close as “feasible” to the National Academies of Sciences’

recommended levels—using the best available technology, treatment techniques, and other

means—taking costs into consideration.8 The act provided EPA with discretionary authority to

issue drinking water regulations for additional contaminants.9 By 1985, EPA had issued interim

regulations with standards for the initial list of contaminants, yet EPA had revised existing

regulations or established regulations for few other contaminants.

In the 99th Congress, concerns about the pace at which EPA issued drinking water regulations

prompted legislation intended to expedite regulation of drinking water contaminants.10 In the Safe

Drinking Water Act Amendments of 1986 (P.L. 99-339), Congress directed EPA to promulgate

drinking water regulations for 83 contaminants by June 1989 and for 25 additional contaminants

every 3 years thereafter.11 Following the 1986 amendments, EPA promulgated new regulations

and revised existing regulations for more than 80 contaminants, attempting to keep pace with the

statutory requirements. Water utilities, state drinking water regulators, and EPA expressed

concern that the regulatory schedule imposed significant burdens and did not prioritize

contaminants based on risk to public health.12 In its report on the 1996 SDWA amendments, the

6 42 U.S.C. §300g-1.

7 U.S. Congress, House Committee on Interstate and Foreign Commerce, Safe Drinking Water Act, 93rd Cong., 2nd

sess., July 10, 1974, H.Rept. 93-1185, pp. 1-11. (SDWA, as amended, comprises Title XIV of the Public Health

Service Act, 42 U.S.C. §§300f-300j-26.) With congressional approval, the Nixon Administration established the U.S.

Environmental Protection Agency (EPA) in 1970 under an executive branch reorganization plan, which consolidated

numerous federal pollution control responsibilities that had been divided among several federal agencies. In 1970,

Congress transferred responsibility for implementation and enforcement of the interstate carrier drinking water

standards from the Public Health Service to EPA. See Appendix B for the 1962 standards, EPA, 25 Years of the Safe

Drinking Water Act: History and Trends, EPA 816-R-99-0007, Washington, DC, December 1999, p. 6.

8 According to the House report accompanying the 1974 act, “the level (i.e., drinking water standard) should be

achievable by large metropolitan water systems treating relatively clean source water.” U.S. Congress, House

Committee on Interstate and Foreign Commerce, Safe Drinking Water Act, 93rd Cong., 2nd sess., July 10, 1974, H.Rept.

93-1185, p. 18.

9 Safe Drinking Water Act (P.L. 93-523), Section 2(a). As discussed in U.S. Congress, Senate Committee on

Environment and Public Works, Safe Drinking Water Act Amendments of 1985, 99th Cong., 1st sess., May 15, 1985,

S.Rept. 99-56.

10 U.S. Congress, Senate Committee on Environment and Public Works, Safe Drinking Water Act Amendments of 1985,

99th Cong., 1st sess., May 15, 1985, S.Rept. 99-56.

11 According to the Senate Debate on these amendments, setting regulatory schedules for specific contaminants is not

normally a legislative function (Sen. Durenberger, “The Safe Drinking Water Act Amendments Conference Report,”

Senate debate, Congressional Record, May 21, 1986, pp. 6284-6301).

12 U.S. Congress, House Committee on Commerce, Safe Drinking Water Act Amendments of 1996, 104th Cong., 2nd

sess., June 24, 1996, H.Rept. 104-632, p. 6.

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Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

House Committee on Commerce stated that, particularly for small water systems, the 1986

regulatory schedule resulted in increased compliance costs without a commensurate increase in

public health protection.13

Adding to these findings, a 1993 outbreak of Cryptosporidiosis in Milwaukee’s public water

supply focused congressional attention on whether the regulatory pace established by the 1986

SDWA amendments reduced EPA’s focus on high-risk contaminants, such as microbial pathogens

that pose acute health risks. In response to calls for “a more streamlined and flexible approach to

controlling drinking water contamination consistent with continued protection of the public

health,”14 the 104th Congress amended SDWA to establish the current health risk-based regulatory

process.15 The House Committee on Commerce stated that the purpose of the Safe Drinking

Water Act Amendments of 1996 was

to help make more effective and more cost-effective Federal regulation of drinking water

and to help small communities pay for improvements to their public water systems, while

ensuring that health protections are maintained or improved.16

Table 1 outlines EPA actions and timelines regarding the regulation of contaminants since the

1974 enactment of SDWA.

13 H.Rept. 104-632, p. 10.

H.Rept. 104-632, p. 6.

15 P.L. 104-182.

16 H.Rept. 104-632, p. 6.

Congressional Research Service

Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

Table 1. SDWA Contaminant Regulation Timeline

Type of Regulatory

Action (# of

Contaminants)

Cumulative #

of Regulated

Contaminants

Date

National Primary Drinking Water

Regulations (NPDWRs)

December 1975

and July 1976

National Interim Primary Drinking Water

Regulations

New (22)

November 1979

Total Trihalomethanes Rule

New (1)

April 1986

Fluoride Rule

Revised (1)

July 1987

Phase I NPDWRs

New (8)

June 1989

Total Coliform Rule

Revised (1)

June 1989

Surface Water Treatment Rule

New (4) and Revised

(1)

January 1991 and

July 1991

Phase II NPDWRs

New (27), Revised

(11), and Deleted (1)

June 1991

Lead and Copper Rule

New (1) and Revised

(1)

July 1992

Phase V NPDWRs

New (22) and Revised

(1)

June 1995

Nickel NPDWR

Remanded (1)

December 1998

Stage I Disinfectant and Disinfection Byproduct

Rule

New (6) and Revised

(1)

December 1998

Interim Enhanced Surface Water Treatment

Rule

New (1) and Revised

(2)

January 2000

Lead and Copper Rule

Revised (2)

December 2000

Radionuclides Rule

New (1) and Revised

(4)

January 2001

Arsenic Rule

Revised (1)

June 2001

Filter Backwash Recycling Rule

Revised (1)

January 2002

Long Term I Enhanced Surface Water

Treatment Rule

Revised (2)

January 2006

Long Term II Enhanced Surface Water

Treatment Rule

Revised (1)

November 2006

Groundwater Rule

New (3)

October 2007

Lead and Copper Rule

Revised (2)

October 2009

Aircraft Drinking Water Rule

Newa

February 2013

Revised Total Coliform Rule

Revised (1)

December 2021

Lead and Copper Rule

Revised (1)

April 2024

Per- and polyfluoroalkyl substances (PFAS)

Rule

New (6)

100

Source: Compiled by CRS from the U.S. Environmental Protection Agency (EPA) website “Regulation Timeline:

Contaminants Regulated Under the Safe Drinking Water Act” at https://www.epa.gov/sdwa/regulation-timelinecontaminants-regulated-under-safe-drinking-water-act.

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Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

The Aircraft Drinking Water Rule addresses microbial contaminants in water served by aircraft that meet

the SDWA definition of a public water system. The contaminants addressed in the rule, total coliform and

Escherichia coli (E. coli), are regulated under an existing rule for other public water systems.

Regulated Public Water Systems

National primary drinking water regulations apply to public water systems. SDWA generally

defines a public water system as a system that provides water through pipes or other conveyances

to at least 15 service connections or that regularly serves at least 25 individuals.17 Primary

enforcement responsibility (primacy) of public water system compliance with SDWA

requirements, including drinking water regulations, may be assumed by states that meet statutory

criteria, under SDWA Section 1413.18

Public water systems can be divided into three subset categories: (1) community water systems,

(2) non-transient non-community water systems, and (3) transient non-community systems.

Community water systems are systems that regularly serve at least 25 individuals year-round.19

Federal drinking water regulations apply to these systems, which collectively provide drinking

water to more than 322 million individuals. As presented in Table 2, more than 50% (26,577) of

community water systems serve 500 or fewer individuals, yet these systems serve roughly 1.4%

of the total population served by community water systems. Non-transient non-community water

systems, such as schools or factories, have their own water supplies and generally serve the same

individuals for more than six months but not year-round. Most drinking water regulations apply

to these systems. Transient non-community water systems, such as campgrounds and gas stations,

provide their own water to transitory customers. Only regulations for contaminants that pose

immediate health risks apply to these systems.

17 42 U.S.C. §300f(4). The act does not specify ownership of public water systems.

18 42 U.S.C. §300g-2. Currently, 49 states, the territories, and the Navajo Nation have applied for and received primacy

for the drinking water program. EPA retains implementation and enforcement authority for Wyoming, the District of

Columbia, and Indian tribes other than the Navajo Nation.

19 42 U.S.C. §300f(15).

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Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

Table 2. Public Water System Statistics

Very Small

Small

Medium

Large

Very Large

500 or

fewer

501 to

3,300

3,301 to

10,000

10,001 to

100,000

100,001 or

Population served

Community

water

system

Total

# of Systems

26,577

13,282

5,013

4,055

469

49,397

Pop. Served

4,525,250

19,114,428

29,518,867

117,103,336

152,492,594

322,754,475

% of Systems

53.80%

26.89%

10.15%

8.21%

0.95%

100%

% of Pop. Served

1.40%

5.92%

9.15%

36.28%

47.25%

100%

NonTransient

noncommunity

system

# of Systems

14,571

2,431

144

17,194

Pop. Served

2,041,430

2,621,545

829,507

1,005,615

453,484

6,951,581

% of Systems

84.74%

14.14%

0.84%

0.26%

0.02%

100%

% of Pop. Served

29.37%

37.71%

11.93%

14.47%

6.52%

100%

Transient

noncommunity

system

# of Systems

73,780

3,039

76,921

Pop. Served

6,974,364

2,841,441

425,958

437,314

10,679,077

% of Systems

95.92%

3.95%

0.11%

0.02%

0.00%

100%

% of Pop. Served

65.31%

26.61%

3.99%

4.10%

0.00%

100%

# of Systems

114,928

18,753

5,242

4,117

472

143,512

Total

Source: Prepared by CRS from EPA’s Safe Drinking Water Information Systems, Water System Summary

report generated on May 13, 2024.

Regulating Contaminants in Public Water Supplies

As revised in 1996, SDWA’s regulatory development provisions reflect themes of prioritizing

contaminants for regulation based on public health risk, considering compliance costs to

communities with health risk reduction benefits, and science-based decisionmaking. The act

requires EPA to identify contaminants that may require regulation, assess health risks based on

the best available peer-reviewed science, conduct a monitoring program to estimate the frequency

and levels of a contaminant’s occurrence, and make determinations of whether a drinking water

regulation is warranted.

EPA’s ability to implement these provisions—and to set scientifically sound standards—depends

on the availability of health effects and occurrence data as well as agency resources to collect

such data, among other factors. For many unregulated contaminants, health effects and

occurrence data may not be available and/or may take time to generate. The availability, as well

as the development, of such data poses challenges for EPA in evaluating contaminants for

regulation and for establishing regulations with enforceable standards for contaminants. (For

further discussion, see “Data Availability and Quality.”)

Identifying Contaminants for Consideration

SDWA requires EPA, every five years, to publish a list of unregulated contaminants known or

anticipated to occur in public water systems that may warrant regulation.20 EPA has termed this

20 SDWA §1412(b)(1)(B); 42 U.S.C. §300g-1(b)(1)(B). This provision directs EPA to consider contaminants defined as

(continued...)

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Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

list the contaminant candidate list (CCL). Prior to publishing a final CCL, EPA is required to

consider contaminant occurrence, to give notice and provide an opportunity for public comment,

and to consult with the scientific community, including the Science Advisory Board.21 In selecting

contaminants for regulatory consideration, SDWA requires EPA to select contaminants that

present the greatest public health concern, taking into consideration a contaminant’s health effects

on specified population subgroups (e.g., infants, children, and pregnant women) who may be at

greater risk due to exposure to a contaminant.22

Over time, EPA has revised the process to identify and list contaminants on the CCL.23 In 2009,

EPA published CCL 3, which was developed using a revised process based on recommendations

and advice from the National Research Council and National Drinking Water Advisory Council

(NDWAC).24 For CCL 3, EPA identified a broad “universe” of 7,500 potential drinking water

contaminants, which was narrowed to 61 on the final CCL through a screening process along with

public and expert input.25 This revised process was intended to be more easily reproducible than

the process EPA used to develop the first and second CCLs.26

Once the CCL is developed, EPA continues to evaluate listed contaminants to inform regulatory

decisionmaking.27 EPA typically divides the listed contaminants into groups: those prioritized for

drinking water research (e.g., health effects, analytical methods, treatment technologies), those

that require additional occurrence data, and those prioritized for future drinking water regulations.

For previous cycles, the agency carried forward contaminants from one CCL to the next to

continue evaluating contaminants. EPA published the final, fifth CCL (or CCL 5) in November

2022, and noted that for this cycle, the agency attempted to improve its process for developing the

CCL based on recommendations from the public and the Science Advisory Board.28 Appendix A

includes details about the first, second, third, fourth, and fifth contaminant candidate lists.

hazardous substances under §101(14) of the Comprehensive Environmental Response, Compensation, and Liability Act

of 1980 (CERCLA; 42 U.S.C. §9601(14)) and substances that are registered as pesticides under the Federal Insecticide,

Fungicide, and Rodenticide Act, as amended (7 U.S.C. §§136 et seq.).

21 The 1978 Environmental Research, Development, and Demonstration Authorization Act (P.L. 95-477) directed EPA

to establish the Science Advisory Board to provide scientific advice to the Administrator (42 U.S.C. §4365).

22 SDWA §1412(b)(1)(C); 42 U.S.C. §300g-1(b)(1)(C).

23 For the first CCL, EPA used screening and evaluation criteria for chemical contaminants from the National Drinking

Water Advisory Council (NDWAC) and convened an expert panel of microbiologists to recommend microbiological

contaminants. EPA also solicited public input through a hotline.

24 NDWAC, “National Drinking Water Advisory Council Report on the CCL Classification Process to the U.S.

Environmental Protection Agency,” May 19, 2004. National Research Council (NRC), “Classifying Drinking Water

Contaminants for Regulatory Consideration,” National Academy Press, Washington, DC. EPA, “Drinking Water

Contaminant Candidate List 3-Draft,” 73 Federal Register 9628-9654, February 21, 2008, at

https://www.federalregister.gov/documents/2008/02/21/E8-3114/drinking-water-contaminant-candidate-list-3-draft.

25 To develop CCL 3, EPA evaluated 284 data sources and selected approximately 7,500 contaminants. EPA then used

specified criteria (i.e., potential to occur in public water systems and potential for public health concern) to reduce the

number of contaminants that EPA included on the preliminary CCL. For the preliminary CCL 3, EPA included 532

contaminants. The agency then evaluated contaminants listed on the preliminary CCL further for their occurrence and

health effects through scoring and “structured classification models” to identify priority contaminants to include on the

final CCL. EPA solicited public input and expert review throughout the development of CCL 3. When finalized, CCL 3

included 116 contaminants.

26 EPA, “Drinking Water Contaminant Candidate List 3-Draft,” 73 Federal Register 9628-9654, February 21, 2008, at

https://www.federalregister.gov/documents/2008/02/21/E8-3114/drinking-water-contaminant-candidate-list-3-draft.

27 For more information, see EPA website “Basic Information on the CCL and Regulatory Determination” at

https://www.epa.gov/ccl/basic-information-ccl-and-regulatory-determination.

28 EPA, “Drinking Water Contaminant Candidate List 5-Final,” 87 Federal Register 68060-68085, November 14, 2022.

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Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

Evaluating Contaminant Occurrence

To gather data on contaminant occurrence at a national level, EPA is required to administer a

monitoring program for unregulated contaminants in public water supplies. SDWA directs EPA to

publish, every five years, a rule (Unregulated Contaminant Monitoring Rule [UCMR]) listing no

more than 30 unregulated contaminants to be monitored by public water systems.29 Only a

nationally representative sample of public water systems serving 10,000 individuals or fewer are

required to conduct monitoring.30 EPA funds the monitoring costs for this representative sample

of small public water systems.31 EPA uses monitoring results from the UCMR to assess the

frequency and levels of a contaminant’s occurrence nationwide.

EPA generally selects the list of unregulated contaminants for a UCMR based on the CCLs, but

may select other unregulated contaminants as well. SDWA directs EPA to include specific

contaminants in the UCMR when such contaminants have been nominated by the governors of

seven or more states.32

For each contaminant included in a UCMR, EPA specifies an analytical method that water system

operators and participating laboratories must use to measure the contaminant in drinking water.33

EPA may be unable to include one or more contaminants of concern in a particular monitoring

rule/cycle if no validated analytical method is available to detect and measure the contaminant in

drinking water. UCMRs set a minimum reporting level (MRL) for each contaminant. MRLs are

based on the capability of the analytical method and are typically set at levels below health-based

reference levels, where established. Prior to finalizing the UCMR, EPA seeks public input by

publishing a proposed contaminant list in the Federal Register.

SDWA requires community water system operators to provide UCMR monitoring results to their

customers in the consumer confidence report.34 Additionally, EPA may require public water

systems to notify consumers specifically about the levels of contaminants for which UCMR

monitoring was required.35 EPA publishes the UCMR monitoring results and reports the number

of detections at or above the MRL, as well as detections above EPA’s health-based reference

levels, when available.

29 SDWA §1445(a)(2); 42 U.S.C. §300j-4(a)(2). This provision requires all systems serving more than 10,000 people

and a sample of smaller systems to monitor for the contaminants. In the America’s Water Infrastructure Act, P.L. 115270, Congress amended §1445 to require public water systems serving between 3,300 and 10,000 individuals to

conduct monitoring—subject to the availability of appropriations. This requirement took effect three years after the

date of enactment of P.L. 115-270 (i.e., October 23, 2021). The National Defense Authorization Act, Fiscal Year 2020

specified for the fifth UCMR that any PFAS with a validated test method not count toward the 30 contaminant limit

(P.L. 116-92, §7311; 15 U.S.C. §8911).

30 SDWA §1445(a)(2); 42 U.S.C. §300j-4(a)(2). EPA estimates that approximately 83% of the population receives

water from public water systems that serve more than 10,000 individuals. This requirement took effect three years after

the date of enactment of P.L. 115-270 (i.e., October 23, 2021).

31 SDWA §1445(a)(2)(C)(ii); 42 U.S.C. §300j-4(a)(2)(C)(ii). This provision directs EPA to cover testing and laboratory

analysis costs for small systems, using funds reserved from the annual DWSRF capitalization grant (SDWA §1452(o);

42 U.S.C. §300j-12(o)).

32 SDWA §1445(a)(2)(B)(ii); 42 U.S.C. §300j-4(a)(2)(B)(ii).

33 The contaminants for which monitoring is required are divided into those for “assessment monitoring” (using test

methods that are widely used) and for “screening survey” (using test methods that are newer and less available).

34 SDWA §1414(c)(4)(B)(v); 42 U.S.C. §300g-3(c)(4)(B)(v). Community water system operators are required to

provide their customers with an annual consumer confidence report on their drinking water quality and SDWA

compliance. Community water systems serving more than 10,000 individuals are required to biannually produce and

distribute such reports.

35 SDWA §1414(c)(1)(C); 42 U.S.C. §300g-3(c)(1)(C); and SDWA §1414(c)(2)(F); 42 U.S.C. §300g-3(c)(2)(F).

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The agency uses UCMRs to gather national occurrence data. These data support evaluation and

prioritization of contaminants on the CCL and inform EPA’s review of contaminants that may

warrant regulation.36 Appendix B contains information on the first, second, third, fourth, and fifth

UCMRs.

Determining Whether or Not to Regulate

Using occurrence and health effects data, EPA is required, every five years, to make a

determination about whether or not to regulate (a regulatory determination [RD]) for at least five

contaminants on the CCL.37 Under SDWA, to make a positive determination to regulate a

contaminant, EPA must find that

•

a contaminant may have an adverse health effect;

it is known to occur or there is a substantial likelihood that it will occur in public

water systems with a frequency and at levels of public health concern; and

in the sole judgment of the Administrator, regulation of the contaminant presents

a meaningful opportunity for health risk reduction for persons served by water

systems.38

In selecting unregulated contaminants for regulatory consideration, SDWA requires EPA to give

priority to contaminants that “present the greatest public health concern.”39 EPA is specifically

required to take into consideration a contaminant’s health effects on specified population

subgroups (e.g., infants, children, pregnant women) that may be at greater risk due to exposure to

a contaminant.40

Before making a final determination, EPA is required to provide notice and opportunity for public

comment on the preliminary RD.41 If EPA makes a determination to regulate a contaminant, the

agency then begins to develop a drinking water regulation. Under the statute, a determination not

to regulate a contaminant is a final agency action and subject to judicial review.42 However, EPA

reconsiders such contaminants for inclusion on the CCL if new occurrence or health effects

information becomes available.43

To evaluate contaminants for regulatory determinations for CCL 3 and CCL 4, EPA used a

process that included three phases—(1) data availability assessment, (2) data evaluation, and (3)

regulatory determination assessment.44 In the final phase, Regulatory Determination Assessment

Phase, EPA evaluates each contaminant using the statutory criteria outlined in SDWA Section

36 EPA, “Revisions to the Unregulated Contaminant Monitoring Regulation for Public Water Systems,” 64 Federal

37 SDWA §1412(b)(1)(B)(ii); 42 U.S.C. 300g-1(b)(1)(B)(ii). Nothing in the statute prevents EPA from making a

regulatory determination outside of the five-year timeline.

38 SDWA §1412(b)(1)(A); 42 U.S.C. §300g-1(b)(1)(A).

39 SDWA §1412(b)(1)(C); 42 U.S.C. §300g-1(b)(1)(C).

40 SDWA §1412(b)(1)(C); 42 U.S.C. §300g-1(b)(1)(C).

41 SDWA §1412(b)(1)(B)(ii); 42 U.S.C. §300g-1(b)(1)(B)(ii).

42 SDWA §1412(b)(1)(B)(ii)(IV); 42 U.S.C. §300g-1(b)(1)(B)(ii)(IV).

43 EPA, “Announcement of Preliminary Regulatory Determinations for Contaminants on the Third Drinking Water

Contaminant Candidate List,” 79 Federal Register 62716-62750, October 20, 2014.

44 EPA, “Announcement of Preliminary Regulatory Determinations for Contaminants on the Third Drinking Water

Contaminant Candidate List,” 79 Federal Register 62716-62750, October 20, 2014.

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1412(b)(1)(A). Under these criteria, EPA evaluates uncertainties or limitations of the health

effects and occurrence data for a contaminant.45

EPA uses available peer-reviewed health effects assessments to derive health reference levels

(HRLs). HRLs are a preliminary estimate of the concentration below which adverse health effects

are unlikely to occur.46 For contaminants with carcinogenic effects (i.e., potential increased risk of

developing certain cancers), EPA develops an HRL using a quantitative estimate of carcinogenic

risk to calculate a level in drinking water equivalent to a one-in-a-million increased risk of cancer

from a lifetime of exposure.47 For noncarcinogenic contaminants, EPA estimates the relative

source contribution, which is the percentage of the general population’s potential exposure from

drinking water to a contaminant (relative to other exposure pathways [including food, inhalation,

and dermal contact]).

EPA reviews the occurrence data for each contaminant, evaluating the number of public water

systems (and the population served) with detections at or above the HRL and above one-half of

the HRL.48 Using these data, EPA evaluates whether the contaminant occurs locally, regionally, or

nationally, and uses these findings to assess whether the contaminant warrants regulation under

the statutory criteria.

The first, second, third, and fourth regulatory determinations are discussed briefly below. (See

Appendix C for additional details.)

Regulatory Determination Cycles

In the first CCL, EPA initially categorized 20 contaminants as having sufficient health effects data

and occurrence information to support RDs, and noted that the agency would use this list to select

five or more contaminants to make regulatory determinations in 2001.49 Subsequently, EPA found

that the available health effects and occurrence data were insufficient to support RDs for 12 of the

20 contaminants.50 EPA selected nine contaminants for the first cycle of regulatory

determinations, and determined that none presented a meaningful opportunity of health-risk

reduction, citing few detections or low risk of adverse health effects, among other reasons.51

45 EPA, Chapter 2: Evaluation of Health and Occurrence Data, EPA Report 815-R-08-012, Washington, DC, June

2008.

46 EPA, “Regulatory Determination 3 Supporting Document,” EPA 815-R-15-014, December 2015. For a nonthreshold

toxicant, such as a carcinogen, EPA derives an estimated concentration below which adverse health effects have a

defined low probability of occurring. EPA states that “an HRL is not a final determination on establishing a protective

level of a contaminant in drinking water for a particular population; it is derived prior to development of a complete

health and exposure assessment and can be considered a screening value.” EPA, “Announcement of Preliminary

Regulatory Determinations for Contaminants on the Fourth Drinking Water Contaminant Candidate List,” 85 Federal

47 EPA, Chapter 2: Evaluation of Health and Occurrence Data, EPA Report 815-R-08-012, Washington, DC, June

2008.

48 EPA, “Announcement of Preliminary Regulatory Determinations for Priority Contaminants on the Contaminant

Candidate List,” 67 Federal Register 38222-38244, June 3, 2002. EPA added sodium to the initial list of eight

contaminants evaluated for possible regulation.

49 EPA, “Announcement of the Drinking Water Contaminant Candidate List,” 63 Federal Register 10285-10286,

March 2, 1998.

50 EPA, “Announcement of Preliminary Regulatory Determinations for Priority Contaminants on the Contaminant

Candidate List,” 67 Federal Register 38222-38244, June 3, 2002.

51 EPA, “Announcement of Preliminary Regulatory Determinations for Priority Contaminants on the Contaminant

Candidate List,” 67 Federal Register 38222-38244, June 3, 2002.

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For the second cycle in 2007, EPA made final determinations not to regulate 11 contaminants, due

to highly regionalized contaminant occurrence or few detections at levels of public health

concern.52 EPA solicited comments and provided an update on assessments of other CCL 2

contaminants, including perchlorate and methyl tertiary-butyl ether (MTBE).53

Regulatory Determination: Perchlorate

In 2008, EPA made a preliminary negative determination for perchlorate, but did not finalize the determination.54

In 2011, EPA reversed the proposed negative determination and published a final regulatory determination that

perchlorate warranted regulation, noting that the agency would begin the process of proposing a drinking water

regulation.55 After proposing a perchlorate regulation in 2019,56 EPA published in 2020 a “Notice of Final Action”

in the Federal Register withdrawing the 2011 positive regulatory determination for perchlorate.57 In 2023, the U.S.

Court of Appeals for the D.C. Circuit vacated EPA’s 2020 withdrawal of its regulatory determination.58 SDWA

requires EPA to propose and finalize a drinking water regulation for perchlorate. Following the 2023 decision, the

spring 2024 Unified Regulatory Agenda did not provide a timeline for a proposed drinking water regulation for

perchlorate and final rule.

For the third cycle in 2014, EPA made a preliminary determination to regulate strontium, and

proposed not to regulate four other contaminants.59 In the final RD 3, EPA determined not to

regulate four contaminants due to low detections and/or low risk to public health.60 For strontium,

EPA delayed a final determination to consider additional newly identified scientific data about the

contribution of other sources of strontium exposure.61

In March 2021, EPA finalized regulatory determinations for contaminants on CCL 4. EPA

determined to regulate two PFAS (i.e., perfluorooctanoic acid [PFOA] and perfluorooctane

sulfonate [PFOS]) and not to regulate six other chemicals.62 In the Federal Register notice for the

preliminary RDs, EPA provided an update on the agency’s efforts to evaluate strontium for

regulation.63

52 EPA, “Drinking Water: Regulatory Determinations Regarding Contaminants on the Second Drinking Water

Contaminant Candidate List—Preliminary Determinations,” 72 Federal Register 24016-24058, May 1, 2007. EPA

stated its intent to finalize a determination by December 2008.

53 EPA, “Drinking Water: Regulatory Determinations Regarding Contaminants on the Second Drinking Water

Contaminant Candidate List-Preliminary Determinations,” 72 Federal Register 24016-24058, May 1, 2007. For

perchlorate, EPA solicited additional information on exposure and associated health effects, and EPA delayed the RD

for MTBE while the agency revised the health risk assessment.

54 EPA, “Drinking Water: Preliminary Regulatory Determination on Perchlorate,” 73 Federal Register 60262-60282,

October 10, 2008.

55 EPA, “Drinking Water: Regulatory Determination on Perchlorate,” 76 Federal Register 7762-7767, February 11,

2011.

56 EPA, “National Primary Drinking Water Regulations: Perchlorate,” 84 Federal Register 30524-30569, June 26,

2019.

57 EPA, “Drinking Water: Final Action on Perchlorate,” 85 Federal Register 43990-44002, July 21, 2020.

58 Natural Resources Defense Council v. U.S. EPA, 20-1335 (U.S. Court of Appeals for the D.C. Circuit 2023).

59 EPA, “Announcement of Preliminary Regulatory Determinations for Contaminants on the Third Drinking Water

Contaminant Candidate List,” 79 Federal Register 62716-62750, October 20, 2014.

60 EPA, “Announcement of Preliminary Regulatory Determinations for Contaminants on the Third Drinking Water

Contaminant Candidate List,” 79 Federal Register 62716-62750, October 20, 2014.

61 EPA, “Announcement of Final Regulatory Determinations for Contaminants on the Third Drinking Water

Contaminant Candidate List,” 81 Federal Register 13-19, January 4, 2016.

62 EPA, “Announcement of Final Regulatory Determinations for Contaminants on the Fourth Drinking Water

Contaminant Candidate List,” 86 Federal Register 12272-12291, March 3, 2021.

63 EPA, “Announcement of Preliminary Regulatory Determinations for Contaminants on the Fourth Drinking Water

Contaminant Candidate List,” 85 Federal Register 14098-14142, March 10, 2020.

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Following EPA’s positive regulatory determination in 2021, the agency made an out-of-cycle

regulatory determination in March 2023. As a part of a proposed rule, EPA proposed that several

other PFAS (i.e., perfluorohexane sulfonic acid [PFHxS], perfluorobutane sulfonic acid [PFBS],

hexafluoropropylene oxide dimer acid [HFPO-DA] and its ammonium salt [also known as GenX

chemical], and perfluorononanoic acid [PFNA]) warranted regulation under SDWA.64 In April

2024, EPA finalized a positive regulatory determination for PFHxS, PFNA, and HFPO-DA,

individually, and for these substances and PFBS, as a mixture.65

Promulgating a Drinking Water Regulation

Once the Administrator determines to regulate a contaminant, SDWA requires EPA to propose a

“national primary drinking water regulation” within 24 months and request public comment on

the proposal. EPA is required to promulgate a final rule within 18 months after the proposal.66

EPA can extend the deadline to publish a final rule for up to nine months by notice in the Federal

For each contaminant that EPA determines to regulate, EPA is required to establish a maximum

contaminant level goal (MCLG) at a level at which no known or anticipated adverse health

effects occur and which allows an adequate margin of safety.68 Regulations also include a

maximum contaminant level (MCL)—an enforceable limit for a contaminant in public water

supplies—or a treatment technique if an MCL is not feasible.69 These regulations can cover

multiple contaminants and generally establish an MCL for each contaminant covered by the

regulation.70

For each drinking water regulation, SDWA requires EPA to identify a list of best available

technologies, treatment techniques, and other means that EPA finds to be feasible for the purposes

of meeting the MCL. In addition, EPA is required to identify treatment technologies that achieve

the MCL and are affordable for small systems.71 Each regulation also establishes associated

monitoring and reporting requirements.

When developing regulations, EPA is required to (1) use the best available, peer-reviewed science

and supporting studies and data; and (2) make publicly available a risk assessment document that

discusses estimated risks, uncertainties, and studies used in the assessment.72

Once finalized, regulations generally take effect three years after promulgation.73 EPA may allow

up to two additional years if the Administrator determines that more time is needed for public

64 EPA, “PFAS National Primary Drinking Water Regulation Rulemaking,” 88 Federal Register 18638-18754, March

29, 2023.

65 EPA, “PFAS National Primary Drinking Water Regulation,” 89 Federal Register 32532-32757, April 26, 2024.

66 SDWA §1412(b)(1)(E); 42 U.S.C. §300g-1(b)(1)(E).

67 SDWA §1412(b)(1)(E); 42 U.S.C. §300g-1(b)(1)(E).

68 SDWA §1412(b)(4)(A); 42 U.S.C. §300g-1(b)(4)(A).

69 SDWA §1412(b)(4)(B); 42 U.S.C. §300g-1(b)(4)(B).

70 By definition, a “primary drinking water regulation” includes an MCL and an MCLG for each contaminant, if

technically and economically feasible. SDWA §1401(1); 42 U.S.C. §300f(1).

SDWA §1412(b)(4)(E)(ii); 42 U.S.C. §300g-1(b)(4)(E)(ii).

72 SDWA §1412(b)(3); 42 U.S.C. §300g-1(b)(3).

73 SDWA §1412(b)(10); 42 U.S.C. §300g-1(b)(10).

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water systems to make capital improvements (states have the same authority for individual water

systems).74

SDWA requires EPA to review each existing national primary drinking water regulation every six

years. The review is intended to identify current health effects assessments, changes in

technology, and/or other factors that would support the revision of a regulation to be more

protective of public health.

Figure 1 outlines the SDWA processes for contaminant evaluation, regulation, and regulatory

review.

Figure 1. Simplified Process for Regulating Contaminants Under SDWA

Source: Modified by CRS from EPA.gov.

Notes: CCL = contaminant candidate list, UCMR = unregulated contaminant monitoring rule, NPDWR =

national primary drinking water regulation.

Maximum Contaminant Level Goals

Drinking water regulations specify a nonenforceable MCLG, which is based solely on health

effects data. Unlike an MCL, the MCLG does not reflect cost or technical feasibility

considerations. For contaminants with carcinogenic effects and for microbial contaminants, EPA

typically sets the MCLG at zero.75

For contaminants with noncarcinogenic effects, EPA derives an MCLG based on a reference dose,

which is an estimate of the amount of a contaminant that a person can be exposed to on a daily

basis that is not anticipated to cause adverse health effects for sensitive life stages and meaningful

populations (e.g., infants, children, pregnant women, the elderly, individuals with a history of

serious illness, or other sensitive subpopulations) over a lifetime.76 This amount incorporates

74 SDWA §1412(b)(10); 42 U.S.C. §300g-1(b)(10). EPA used this authority to provide two additional years for

community water systems serving 10,000 or fewer people to comply with the revised arsenic rule. EPA, “Proposed

Rule: Arsenic and Clarifications to Compliance and New Source Contaminants Monitoring,” 65 Federal Register

38888-38983, June 22, 2000.

75 For more information, see EPA website “How EPA Regulates Drinking Water Contaminants” at

https://www.epa.gov/sdwa/how-epa-regulates-drinking-water-contaminants#standards.

76 EPA, “Announcement of Preliminary Regulatory Determinations for Contaminants on the Fourth Drinking Water

Contaminant Candidate List,” 85 Federal Register 14098-14142, March 10, 2020.

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uncertainty factors to provide a margin of protection for sensitive subpopulations and to account

for uncertainties in the data.77

In developing an MCLG for noncarcinogens, EPA also estimates the general population’s

exposure to a contaminant from drinking water and other sources (e.g., food, dust, soil, and air).

After considering other exposure routes, EPA estimates the proportion of exposure attributable to

drinking water (i.e., the relative source contribution [RSC]).78 When exposure information is not

available, EPA uses a default assumption that 20% of exposure to a contaminant is attributable to

drinking water. EPA applies the RSC to ensure that an individual’s total exposure from all sources

remains within the estimated protective level.79 The MCLG provides the basis for calculating an

MCL.80

Feasibility and Maximum Contaminant Levels

SDWA generally requires EPA to set the MCL as close to the MCLG as “feasible.”81 The act

defines “feasible” to mean feasible with the use of the best available (and field demonstrated)

treatment technologies, taking cost into consideration.82 The level at which EPA is able to set the

MCL is determined by the ability of a treatment technology to reduce a contaminant to a certain

level. EPA’s ability to set the MCL at the MCLG also depends on the availability of a test method

that is sensitive enough to detect the contaminant at the MCLG. For contaminants regulated for

noncarcinogenic effects, EPA generally has set the enforceable standard at the same level as the

MCLG. If it is not technologically or economically feasible to ascertain the level of a contaminant

in drinking water, EPA may establish a treatment technique in lieu of an MCL.83 For example,

EPA’s Lead and Copper Rule includes a treatment technique—primarily relying on corrosion

control, among other actions—because lead and/or copper generally enters the water after it

leaves the plant.84

When developing an MCL that is feasible, EPA identifies and considers the costs to “large” water

systems, as guided by legislative history.85 Large water systems, serving more than 10,000

individuals, comprise roughly 9% of the number of community water systems and serve a

majority (83%) of individuals regularly served by such systems.86 By considering the costs to

these systems, Congress intended that MCLs would be established at protective levels that are

77 EPA, “Announcement of Preliminary Regulatory Determinations for Contaminants on the Fourth Drinking Water

Contaminant Candidate List,” 85 Federal Register 14098-14142, March 10, 2020.

78 Other exposure routes include food ingestion, inhalation, and dermal contact.

79 See, for example, EPA, Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA), EPA 822-R-16-005,

May 2016, p. 32, https://www.epa.gov/sites/default/files/2016-05/documents/pfoa_health_advisory_final-plain.pdf.

80 The Safe Drinking Water Act does not prohibit states from setting stricter standards.

81 SDWA §1412(b)(4)(B); 42 U.S.C. §300g-1(b)(4)(B). EPA may set a standard at other than the feasible level if the

feasible level would lead to an increase in health risks by increasing the concentration of other contaminants or by

interfering with the treatment processes used to comply with other SDWA regulations. In such cases, the standard or

treatment techniques must minimize the overall health risk (SDWA §1412(b)(5); 42 U.S.C. §300g-1(b)(5)).

82 SDWA §1412(b)(4)(D); 42 U.S.C. §300g-1(b)(4)(D).

83 SDWA §1412(b)(7)(A); 42 U.S.C. §300g-1(b)(7)(A).

84 40 C.F.R. §§141.80-141.91.

85 The meaning of “large” water system has changed over time. Prior to the 1996 SDWA amendments, EPA’s 1991

Lead and Copper Rule identified large systems as those serving 50,000 or more individuals, as guided by legislative

history. The 1996 SDWA Amendments added SDWA §1412(b)(4)(ii), which required EPA to identify compliance

technologies for small water systems defined as those serving 10,000 or fewer individuals.

86 From EPA’s “Safe Drinking Water Information Systems: Water System Summary” report at https://ofmpub.epa.gov/

apex/sfdw/f?p=108:1:::NO:1::. Report generated on May 13, 2024. The search parameters were “public water

systems.”

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achievable for large systems, and thus provide affordable drinking water to a majority of

individuals served by public water systems. This approach may make compliance with certain

regulations less affordable for small water systems. To address affordability, SDWA includes

numerous provisions intended to support small system compliance. For discussion of some of

these provisions, see “Variances and Exemptions.”

Additional Health Risk Reduction and Cost Considerations

SDWA provides EPA with limited authority to establish an MCL at a level other than the

“feasible” level in certain circumstances. EPA may use this authority if, based on a “Health Risk

Reduction Cost Analysis,” the Administrator determines that the benefits of the feasible level

“would not justify the costs of complying with the level.”87 In such a case, EPA may—after

providing opportunity for public comment—set the standard at a level that “maximizes health risk

reduction benefits at a cost that is justified by the benefits.” However, this authority is not

available if the benefits that would be experienced by (1) large water systems, and (2) those other

systems unlikely to receive small system variances (e.g., systems serving up to 10,000 persons),

would justify the costs.88 EPA has used this authority to establish MCLs at a level that was higher

(i.e., less protective) than what would be “feasible” for two contaminants—uranium and arsenic.89

For both contaminants, EPA established the MCL at a level higher than what was determined

“feasible” because the agency estimated that the costs to treat these contaminants would be

incurred primarily by small water systems.90

Health Risk Reduction Cost Analysis

Concurrent with proposing a regulation, SDWA requires that EPA publish and seek public

comment on a “health risk reduction and cost analysis” (HRRCA) for each contaminant covered

by the proposed regulation.91 While several congressional and presidential initiatives require

certain federal agencies to evaluate costs and benefits of rulemakings,92 SDWA outlines the

specific costs and benefits that EPA is required to estimate when preparing an HRRCA and

87 SDWA §1412(b)(6)(A); 42 U.S.C. §300g-1(b)(6)(A).

88 SDWA §1412(b)(6)(B); 42 U.S.C. §300g-1(b)(6)(B).

89 For uranium, EPA revised the MCL from 20 µg/L—which EPA considered the “feasible” level—to 30 µg/L due to

(1) the generation of additional health effects studies that indicate that “there is not a predictable difference in health

effects due to exposure” between the two levels, and (2) the cost differences between treating to the two different levels

(65 Federal Register 76708-76753). In EPA’s proposed arsenic rule, EPA determined that 3 µg/L was “feasible.” EPA

used this authority to set the revised MCL at a level where the benefits from health risk reduction outweigh the costs, at

10 µg/L (66 Federal Register 6976-7066). As with the previous standard (set at 50 µg/L), the MCL applies only to

community water systems.

90 EPA, “National Primary Drinking Water Regulations; Radionuclides; Final Rule,” 65 Federal Register 76715,

December 7, 2000. EPA, “National Primary Drinking Water Regulations; Arsenic and Clarifications to Compliance

and New Source Contaminants Monitoring,” 66 Federal Register 7033-7034, January 22, 2001. Small water systems

primarily rely on groundwater for their drinking water source. Some groundwater sources have naturally occurring

contaminants such as arsenic and radionuclides (including uranium). Under these rules, such system that rely on

groundwater, which are primarily small water systems, would face costs to treat for such naturally occurring

contaminants.

91 EPA may promulgate an interim standard without first preparing a health risk reduction and cost analysis or making

a determination as to whether the benefits of a regulation would justify the costs if the Administrator determines that a

contaminant presents an urgent threat to public health. SDWA §1412(b)(1)(D); 42 U.S.C. 300g-1(b)(1)(D).

Cryptosporidium is exempt from the health risk reduction and cost analysis requirement (SDWA §1412(b)(6)(C); 42

U.S.C. 300g-1(b)(6)(C)).

92 For more information, see CRS Report R41974, Cost-Benefit and Other Analysis Requirements in the Rulemaking

Process, coordinated by Maeve P. Carey.

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requires EPA to present the uncertainties of such an analysis.93 The HRRCA is intended to

provide a transparent analysis of the costs and benefits, calculated using the available science, as

well as EPA’s assumptions when developing a drinking water regulation. To prepare an HRRCA,

EPA estimates the baseline conditions prior to drinking water regulation (based on contaminant

occurrence and effectiveness of existing treatment technologies already in use); estimates

national-level costs and benefits associated with the regulation of a specific contaminant; and

assesses distributional impacts and equity concerns.94

At the public water system level, EPA estimates costs associated with treatment (e.g., installation

and operation of contaminant removal technologies), training for staff, monitoring and analyzing

water samples, and management and oversight.95 In addition, the analysis may include costs to

primacy agencies to enforce regulations. SDWA directs EPA to evaluate costs for compliance

with the proposed MCL (and alternative MCLs), but specifically excludes compliance costs for

other proposed or promulgated drinking water regulations.96

When developing an HRRCA, EPA calculates primarily the benefits of avoided mortality or

morbidity (illness) from reduced exposure to a contaminant through drinking water for specified

sensitive subpopulations and for the general population. As provided in SDWA, sensitive

subpopulations include

infants, children, pregnant women, the elderly, individuals with a history of serious illness,

or other subpopulations that are identified as likely to be at greater risk of adverse health

effects due to exposure to contaminants in drinking water than the general population.97

EPA quantifies health benefits through a variety of methods, primarily estimating the cost of

illness or the cost of reduced physical and mental well-being. Other methods include estimating

willingness-to-pay to avoid negative health impacts. EPA may include other quantifiable and

nonquantifiable benefits such as “enhanced aesthetic benefits” (e.g., improved taste), avoided

materials damage (e.g., reduced corrosivity of drinking water), avoided costs of household or

water system actions to prevent contamination, as well as non-use benefits, among others.98

93 SDWA §1412(b)(3)(C); 42 U.S.C. 300g-1(b)(3)(C).

94 EPA, Preliminary Health Risk Reduction and Cost Analysis: Revised National Primary Drinking Water Standards

for Radionuclides, Cambridge, MA, January 2000.

95 For more information, see EPA website, “SDWA Economic Analysis” at https://www.epa.gov/dwregdev/economicanalysis-and-statutory-requirements.

96 SDWA §1412(b)(3)(C)(i)(III); 42 U.S.C. 300g-1(b)(3)(C)(i)(III).

97 SDWA §1412(b)(3)(C)(i)(V); 42 U.S.C. §300g-1(b)(3)(C)(i)(V).

98 For more information, see EPA website “National Benefits Analysis for Drinking Water Regulations” at

https://www.epa.gov/sdwa/national-benefits-analysis-drinking-water-regulations.

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Health Advisories

For unregulated contaminants, health effects and/or occurrence data often are limited. SDWA authorizes EPA to

issue health advisories for contaminants in drinking water that are not regulated under the act.99 Health advisories

provide information for states, water suppliers, and public health officials on health effects, test methods, and

treatment technologies for specific contaminants. Health advisories are nonenforceable and intended to help

states, water suppliers, and others address contaminants for which federal drinking water standards have not been

established. Health advisories include levels for contaminants in drinking water that can be used to address

different circumstances and exposure durations (e.g., 1 day, 10 days, a lifetime) and technical guidance on

identifying, measuring, and treating contaminants. EPA has issued health advisories to address various

circumstances: when contaminants do not meet the statutory criteria to warrant a national primary drinking water

regulation, as an interim measure while EPA evaluates a contaminant for regulation, or to address a short-term

incident or spill.

EPA sets the health advisory levels at concentrations that are expected to be protective of the most sensitive

subpopulations (e.g., nursing infants) from any deleterious health effects, with a margin of protection, over the

specified duration of exposure. Similar to the calculation of an MCLG, health advisory levels account for exposure

from other contaminant sources (e.g., dermal contact, inhalation, and food ingestion).

Some states have used health advisories to inform their own state-specific drinking water regulations. EPA has

issued health advisories for more than 200 contaminants to address different circumstances and subsequently

established regulations for many of these contaminants.100

Variances and Exemptions

As discussed above, national primary drinking water regulations consider the costs to large water

systems, which provide water to 83% of the total population regularly served by public water

systems, yet comprise roughly 9% of the total number of community water systems.101 The

remaining 91% of water systems that serve 10,000 or fewer individuals may lack technical,

managerial, and financial capacity, leading to regulatory compliance challenges. Congress has

long recognized the compliance challenges of “small” systems and has added a suite of provisions

to SDWA to address such challenges. Among these, SDWA includes provisions that provide for

“variances” from a drinking water standard and “exemptions” (i.e., additional time for

compliance with a standard) from drinking water regulations, under specified circumstances.

Specifically for small systems, states may provide variances if EPA cannot identify an affordable

technology that reduces the contaminant to the MCL.102 If EPA identifies no such technology,

then the agency is required to identify affordable variance technologies that may not meet the

MCL.103 After identifying variance technologies, states may grant small system variances to

systems serving 3,300 or fewer persons if through treatment, an alternative water source, or

restructuring, a system cannot afford to comply with the MCL and the variance ensures adequate

protection of public health.104 Under this type of variance, a state would allow the system to use a

99 SDWA §1412(b)(1)(F); 42 U.S.C. §300g-1(b)(1)(F).

100 EPA, 2018 Edition of the Drinking Water Standards and Health Advisories Tables, March 2018,

https://www.epa.gov/system/files/documents/2022-01/dwtable2018.pdf.

101 From EPA’s “Safe Drinking Water Information Systems: Water System Summary” report at

https://ofmpub.epa.gov/apex/sfdw/f?p=108:1:::NO:1::. Report generated on May 13, 2024. The search parameters were

“public water systems.” For more information about SDWA and small water systems, see CRS Report R47315, Small

Water Systems: Selected Safe Drinking Water Act (SDWA) Provisions, by Elena H. Humphreys.

102 SDWA §1415(e); 42 U.S.C. §300g-4(e). In addition, SDWA §1415 authorizes states to grant a public water system

a variance from an MCL if the untreated source water quality prevents meeting MCL even after application of the best

technology, and the variance does not result in an unreasonable risk to health.

103 SDWA §1412(b)(15); 42 U.S.C. §300g-1(b)(15).

104 SDWA §1415(e); 42 U.S.C. §300g-4(e).

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variance technology to comply with a regulation. With EPA approval, states may also grant

variances to systems serving between 3,301 and 10,000 persons. Variances are not available for

microbial contaminants. For every drinking water regulation, EPA has determined that

compliance technologies for all MCLs are affordable for small systems; therefore, small system

variances are not available.

SDWA Section 1416 authorizes states to grant public water systems temporary exemptions from

drinking water regulations if a system cannot comply for other compelling reasons (including

costs). An exemption is intended to give a water system additional time to come into compliance

with a regulation and is limited to situations where an exemption would not result in an

unreasonable health risk. Exemptions can be issued to a qualified system for up to three

additional years beyond the regulation’s effective date. Systems serving 3,300 or fewer persons

may receive a maximum of three additional two-year extensions for total exemption duration of

nine years.

Six-Year Reviews

SDWA directs EPA, every six years, to review and revise, if necessary, each regulation and

requires that any revision maintain or provide greater health protection.105 EPA considers possible

revisions if the revisions could improve the level of public health protection or achieve cost

savings while maintaining or improving public health protection.

Since 1996, EPA has completed three cycles of the “Six-Year Review.” For the first cycle, EPA

determined to revise the Total Coliform Rule.106 For the second cycle in 2010, EPA determined to

revise the regulations for four contaminants (i.e., acrylamide, epichlorohydrin,

tetrachloroethylene, and trichloroethylene).107 For the third cycle in 2017, EPA determined to

revise eight regulations, which are part of the following rules: (1) the Stage 1 and the Stage 2

Disinfectants and Disinfection Byproducts Rules, (2) the Surface Water Treatment Rule, (3) the

Interim Enhanced Surface Water Treatment Rule, and (4) the Long Term Enhanced Surface Water

Treatment Rule.108 For the fourth cycle in 2024, EPA determined that no additional drinking water

regulations warranted revision.109

Table 3 includes a summary of EPA’s actions to evaluate or revise contaminants for regulation

under the Safe Drinking Water Act since the 1996 SDWA amendments that established the act’s

current process.

105 SDWA §1412(b)(9); 42 U.S.C. §300g-1(b)(9).

106 EPA, “National Primary Drinking Water Regulations; Announcement of Completion of EPA’s Review of Existing

Drinking Water Standards,” 68 Federal Register 42908-42929, July 18, 2003.

107 EPA, “National Primary Drinking Water Regulations; Announcement of the Results of EPA’s Review of Existing

Drinking Water Standards and Request for Public Comment and/or Information on Related Issues,” 75 Federal

108 EPA, “National Primary Drinking Water Regulations; Announcement of the Results of EPA’s Review of Existing

Drinking Water Standards and Request for Public Comment and/or Information on Related Issues,” 82 Federal

109 EPA, Six-Year Review 4 of Drinking Water Standards, July 2024, https://www.epa.gov/dwsixyearreview/six-yearreview-4-drinking-water-standards.

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Table 3. EPA’s Drinking Water Contaminant Regulatory Development Actions

First

Second

Third

Fourth

Fifth

1998

2005

2009a

2016

2022

contaminants

51 contaminants

116

contaminants

109

contaminants

81 contaminants

or groups

1999

2007

2012

2016

2021

contaminants

25 contaminants

30 contaminants

Regulatory

Determination

(RD)

2003

2008

2016

2021

Evaluated

9 contaminants

11 contaminants

(including

perchlorate)

5 contaminants

8 contaminants

Determination to

Regulate

None

Noneb

Nonec

EPA determined

to regulate

PFOA and

PFOSd

Contaminant

Candidate List

(CCL)

Unregulated

Contaminant

Monitoring

Rule (UCMR)

In 2023, EPA

made an out-ofcycle

determination to

regulate six other

per- and

polyfluoroalkyl

substances

(PFAS)

Six-Year

Reviews

2003

2010

2017

2023

Evaluated

69 national

primary

drinking water

regulations

(NPDWRs)

71 NPDWRs

76 NPDWRs

All NPDWRs

except PFAS

Chosen for

Revision

1 NPDWR

4 NPDWRs

8 NPDWRs

No Additional

NPDWRs

Source: Compiled by CRS from epa.gov. For additional detail on CCLs, UCMRs and RDs, and specific

references, see Appendix A, Appendix B, and Appendix C respectively.

a. Over time, EPA has revised its approach to finalizing the CCL. For CCL 3, EPA identified a broad “universe”

of 7,500 potential drinking water contaminants, which the agency narrowed to 116 for the final list through

a screening process.

b. In 2011, the Administrator determined that regulation was needed for perchlorate, reversing the 2008

negative determination (76 Federal Register 7762-7767). In July 2020, the Administrator withdrew the 2011

determination to regulate perchlorate, and made a final determination not to regulate perchlorate (85

Federal Register 43990-44002). In 2023, the U.S. Court of Appeals for the D.C. Circuit vacated EPA’s 2020

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withdrawal of its regulatory determination. Therefore, SDWA requires EPA to propose and finalize a

drinking water regulation for perchlorate. Following the 2023 decision, the spring 2024 Unified Regulatory

Agenda did not provide a timeline for a perchlorate proposed drinking water regulation and final rule.

In 2016, EPA delayed the determination for strontium to consider additional data (81 Federal Register 13-19).

In March 2021, EPA finalized determinations to regulate perfluorooctanoic acid [PFOA] and

perfluorooctane sulfonate [PFOS] in 86 Federal Register 12272-12291.

Considerations for Regulatory Determinations

SDWA broadly outlines the regulatory assessment and development process, yet several technical

and policy considerations arise when implementing the process. Technical considerations include

the availability and quality of health effects and occurrence data, and the availability of validated

analytical test methods, as well as sufficient laboratory capacity and availability of a feasible

treatment technology. Overarching considerations include prioritizing among thousands of

potential contaminants, addressing contaminants that may not meet the act’s criteria to warrant

regulation but still generate public health concern, and competing priorities for agency resources

to support drinking water contaminant evaluation and regulation development.

Data Availability and Quality

Implementation of the act’s process for evaluating contaminants for regulation and developing

drinking water regulations depends on data availability and quality. For unregulated

contaminants, EPA may lack the necessary health effects and/or occurrence data to consider such

contaminants for regulation. To add a contaminant to the CCL, EPA requires initial data to

characterize the contaminant’s occurrence and adverse health effects.110 Similarly, when selecting

contaminants for monitoring as a part of a UCMR, EPA evaluates a contaminant’s health effects,

prioritizing contaminants associated with carcinogenic health effects.111 To make a regulatory

determination for a contaminant, EPA requires a peer-reviewed risk assessment and nationally

representative occurrence data.112 Without these data, EPA is unable to evaluate whether a

contaminant meets the statutory criteria for regulation. For example, as a part of RD 4, EPA

identified that 84 contaminants under consideration lacked either of these data.113

To establish an MCLG and drinking water standard, EPA requires a peer-reviewed risk

assessment to evaluate a contaminant’s health effects, as well as to identify and account for

effects on the most sensitive subpopulations.114 When developing an HRRCA, EPA requires

health effects data to estimate benefits associated with reducing the risk of exposure as well as

occurrence data and field-tested treatment technologies to estimate the cost of treatment needed to

comply. Without data to estimate the costs and benefits of regulating a contaminant, EPA is

unable to calculate the benefits from reduced health risks or the regulatory costs to communities

and others.

110 EPA, “Drinking Water Contaminant Candidate List 3-Draft,” 73 Federal Register 9628-9654, February 21, 2008.

111 EPA, “Revisions to the Unregulated Contaminant Monitoring Regulation (UCMR 3) for Public Water Systems,” 76

Federal Register 11713-11737, March 3, 2011.

112 EPA, “Drinking Water Contaminant Candidate List 4-Draft,” 80 Federal Register 6076-6084, February 4, 2015.

113 EPA, “Preliminary Regulatory Determinations for Contaminants on the Fourth Contaminant Candidate List,” 85

Federal Register 14098-14142, March 10, 2020.

114 EPA, “Preliminary Regulatory Determinations for Contaminants on the Third Contaminant Candidate List,” 79

Federal Register 62716-62750, October 20, 2014.

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The absence of sufficient data for unregulated contaminants has limited EPA’s implementation of

SDWA regulatory development provisions.115 EPA has often been unable to include unregulated

contaminants for regulatory determinations due to an absence of a peer-reviewed risk assessment

or nationally representative occurrence data. For several contaminants evaluated for RDs (e.g.,

perchlorate, strontium), EPA delayed finalizing determinations to collect additional data.116 In a

2011 report, GAO concluded that insufficient data to characterize contaminant occurrence or

health effects had impeded EPA progress in regulating contaminants in drinking water.117

Availability of Analytical Methods and Laboratory Capacity

EPA’s ability to develop contaminant occurrence data for the SDWA regulatory determinations

depends on the availability of analytical test methods and laboratory capacity. For each

contaminant in an UCMR, EPA requires a widely available analytical test method and sufficient

laboratory capacity to support nationwide monitoring.118 As a part of the UCMR, EPA may assist

with the development of new analytical methods and/or identify consensus organizationdeveloped methods.119

In preparation of a UCMR, laboratories across the country must receive EPA approval certifying

that they have demonstrated that they can perform the method with replicable results.120 EPA

requires laboratories that seek to participate in UCMRs to apply and receive approval through

EPA’s Laboratory Approval Program, which requires demonstrated method proficiency with

analytical standards.121 EPA cannot select a contaminant for a UCMR without a validated

analytical method and sufficient laboratory capacity to support a national monitoring program.

The availability of an analytical test method also informs EPA’s ability to establish an MCL as

close to the MCLG as “feasible.” To assess feasibility, EPA first evaluates the sensitivity of the

test method to detect a contaminant at levels close to the MCLG. Without a method that could

detect a noncarcinogenic contaminant at the “goal” level, EPA would not be able to set an MCL at

the MCLG.122

115 See, for example, Table 2, “Information Gaps for the CCL 2 Chemical Contaminants,” EPA, “Drinking Water:

Regulatory Determinations Regarding Contaminants on the Second Drinking Water Contaminant Candidate List,” 73

Federal Register 44251-44261, July 30, 2008.

116 EPA, “Drinking Water: Regulatory Determinations Regarding Contaminants on the Second Drinking Water

Contaminant Candidate List-Preliminary Determinations,” 72 Federal Register 24016-24058, May 1, 2007. EPA,

“Announcement of Final Regulatory Determinations for Contaminants on the Third Drinking Water Contaminant

Candidate List,” 81 Federal Register 13-19, January 4, 2016.

117 GAO, EPA Should Improve Implementation of Requirements on Whether to Regulate Additional Contaminants, 11254, May 27, 2011, at https://www.gao.gov/products/GAO-11-254.

118 EPA, “Drinking Water Contaminant Candidate List 4-Draft,” 80 Federal Register 6076-6084, February 4, 2015.

119 EPA, “Revisions to the Unregulated Contaminant Monitoring Regulation (UCMR 3) for Public Water Systems,” 76

Federal Register 11713-11737, March 3, 2011. For UCMR 3, EPA developed six analytical methods and identified

four equivalent methods from consensus organizations (e.g., Standard Methods and ASTM International).

120 EPA, “Revisions to the Unregulated Contaminant Monitoring Regulation (UCMR 3) for Public Water Systems,” 76

Federal Register 11713-11737, March 3, 2011.

121 EPA, “Revisions to the Unregulated Contaminant Monitoring Regulation (UCMR 3) for Public Water Systems,” 76

Federal Register 11713-11737, March 3, 2011.

122 For contaminants with carcinogenic effects, EPA sets the MCLG at zero. Without an available treatment technology

to reduce a carcinogen to zero, EPA would be unable to set the MCL at the MCLG.

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Consideration of Contaminant Group Regulations

The SDWA definition of a “primary drinking water regulation” specifies that each contaminant has an MCL or a

treatment technique. EPA has regulated some contaminants as groups (e.g., different types of disinfection

byproduct groups [total trihalomethanes and total haloacetic acids], and gross alpha radionuclides, etc.). EPA has

made regulatory determinations for individual contaminants, including as a mixture.

In 2010, EPA released its Drinking Water Strategy, which included a principle to address drinking water

contaminants as groups so that drinking water protection can be achieved cost effectively.123 To issue a single

drinking water regulation for a group of contaminants, EPA stated that, at a minimum, all the contaminants must

have the same specific adverse health effect (e.g., cancer, endocrine effects, or developmental effects), be

measured by the same analytical methods, be treated with the same treatment technology or treatment technique,

and/or been shown to occur individually (and possibly co-occur).124 For RD 3, EPA considered regulating several

contaminants as a group, but ultimately decided to address one group of drinking water compounds, carcinogenic

volatile organic compounds, through a separate regulatory process.125

For certain contaminants, group regulation may pose challenges. Certain contaminants may have some broad

chemical similarities; however, such contaminants may have different health effects or require different sampling

methods and treatment technologies or do not yet have analytical methods developed to detect their occurrence

in drinking water. Establishing an enforceable standard for a group of contaminants also poses a technical challenge

as the health risk reduction and cost analysis requires assessment of the risk reduction benefits and compliance

costs for each contaminant. Individual contaminants may have varying MCLs depending on the treatment costs and

health effects for each contaminant, which would affect the treatment technologies available to public water

systems to comply with such a regulation.

Congressional Interest

Congressional interest in SDWA regulatory development provisions has centered on EPA’s

implementation of these provisions, as well as the functionality of the current process.126 Since

the 1996 SDWA amendments, EPA has finalized positive regulatory determinations for seven

contaminants. Since 1996, EPA has considered thousands of chemicals for potential regulation,

and developed health effects and occurrence data for numerous unregulated contaminants. The

agency has also revised several drinking water regulations to tighten standards and has revised

and expanded other existing regulations to establish MCLs for additional contaminants. In April

2024, EPA promulgated a national primary drinking water regulation for six PFAS based on a

finalized positive regulatory determination.

In the 117th and 118th Congresses, Members introduced legislation regarding SDWA’s regulatory

development provisions primarily intended to expedite the regulation of PFAS.127 Since EPA’s

finalization of the drinking water regulation for six PFAS, some Members have raised concerns

that EPA’s regulation “lacks robust scientific support and did not fully consider the financial

123 EPA, A New Approach to Protecting Drinking Water and Public Health, EPA 815F10001, March 2010,

https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1006RG2.txt.

124 EPA, “Preliminary Regulatory Determinations for Contaminants on the Third Contaminant Candidate List,” 79

Federal Register 62715-62750, October 20, 2014, at https://www.regulations.gov/document?D=EPA-HQ-OW-20120155-0001.

125 EPA also considered regulating other contaminants as a group. For further discussion, see EPA, “Preliminary

Regulatory Determinations for Contaminants on the Third Contaminant Candidate List,” 79 Federal Register 6271662750.

126 Recent appropriations acts directed EPA to use specified funds to support MCL development and to brief the

conferees on the agency’s plans to develop MCLs for specific drinking water contaminants.

127 See, for example, Senate Committee on Environment and Public Works, “Stakeholder Comment on Draft PFAS

Legislation,” press release, June 22, 2023.

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strains for compliance, particularly for rural and historically disadvantaged communities.”128

These were concerns, among others, about EPA’s implementation of the SDWA regulatory

development provisions that were the subject of congressional debate in the 116th Congress.

Members were heavily focused on SDWA’s regulatory development provisions during the 116th

Congress due to widespread concerns about PFAS contamination. Some Members raised

concerns that the act’s process was lengthy and complicated and did not allow for the timely

regulation of contaminants of concern in drinking water.129 Other Members expressed concern

that proposals to expedite regulation by removing elements of SDWA regulatory development

provisions (e.g., the requirement to use peer-reviewed science or a health risk-based approach)

could result in compliance costs and affordability challenges for communities to address

contaminants that may not pose a significant threat to public health or regulations that are not

based on the best available, peer-reviewed science.130 This debate was heightened prior to EPA’s

positive regulatory determination for PFAS in 2021.131

When federal drinking water standards are absent, states are authorized to (and have) issued

regulations for contaminants, which may vary from state to state. Some Members have argued

that this patchwork of regulation undermines public confidence in drinking water quality.132 Other

Members caution that proposals to amend SDWA to increase regulatory pace would add to states’

financial burdens without meaningful health protection, as drinking water regulation enforcement

is generally a state responsibility.133 Other issues include how costs are considered in the

standard-setting process, whether the development of a “feasible” standard is sufficiently

protective of sensitive subpopulations, and the affordability of regulations for small and

disadvantaged communities.

Some stakeholders have concerns about the third regulatory determination criterion, which gives

some discretion to the Administrator to assess what constitutes a “meaningful opportunity for

health risk reduction.”134 Others have argued that proposals that focus on the quantity of drinking

128 Senate Committee on Environment and Public Works, “Capito Statement on EPA’s New Drinking Water Standard

for PFAS,” press release, April 10, 2024.

129 See, for example, U.S. Congress, House Committee on Energy and Commerce, Subcommittee on Environment and

Climate Change, There’s Something in the Water: Reforming Our Nation’s Drinking Water Standards, Testimony of

Subcommittee Chairman Tonko, 116th Cong., 2nd sess., July 28, 2020.

130 U.S. Congress, House Committee on Energy and Commerce, Subcommittee on Environment and Climate Change,

There’s Something in the Water: Reforming Our Nation’s Drinking Water Standards, Testimony of Ranking Member

Walden, 116th Cong., 2nd sess., July 28, 2020.

131 In the 116th Congress, legislation was introduced to direct EPA to regulate specific contaminants (e.g., PFOA and

PFOS).131 Other bills would have established a different regulatory process and deadlines for specific contaminants or

groups of contaminants (i.e., PFAS). On occasion, Congress has directed EPA to promulgate a regulation for a

particular contaminant within a specified time frame. For example, in the Safe Drinking Water Amendments of 1996

(P.L. 104-182), the 104th Congress directed EPA to regulate radon, propose a new arsenic standard, and evaluate sulfate

for regulation (SDWA §1412(b)(12); 42 U.S.C. §300g(b)(12); SDWA §1412(b)(13); 42 U.S.C. §300g(b)(13)).

132 U.S. Congress, House Committee on Energy and Commerce, Subcommittee on Environment and Climate Change,

There’s Something in the Water: Reforming Our Nation’s Drinking Water Standards, Testimony of Subcommittee

Chairman Tonko, 116th Cong., 2nd sess., July 28, 2020.

133 U.S. Congress, House Committee on Energy and Commerce, Subcommittee on Environment and Climate Change,

There’s Something in the Water: Reforming Our Nation’s Drinking Water Standards, Testimony of Ranking Member

Walden, 116th Cong., 2nd sess., July 28, 2020. SDWA §1413 (42 U.S.C. §300g-2) requires EPA to delegate primary

enforcement authority for SDWA regulations to states that meet certain criteria. Currently, 49 states, the territories, and

the Navajo Nation have applied for and received primacy for the drinking water program. EPA retains implementation

and enforcement authority for Wyoming, the District of Columbia, and Indian tribes other than the Navajo Nation.

134 See, for example, U.S. Congress, House Committee on Energy and Commerce, Subcommittee on Environment and

Climate Change, There’s Something in the Water: Reforming Our Nation’s Drinking Water Standards, 116th Cong., 2nd

sess., July 28, 2020, testimony from Natural Resources Defense Council.

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water regulations, or the presence of a contaminant rather than risk, may lead EPA to focus

agency resources on promulgating regulations without a scientific basis or on regulating “lower

priority” contaminants with fewer health impacts to meet statutory quotas, as happened in the

1986 amendments, which directed EPA to regulate 25 contaminants every 3 years.135

Other concerns have involved how, under SDWA, regulatory costs to water systems and customer

affordability are considered when EPA sets a drinking water standard. Particularly for small water

systems, and communities with declining populations or economies, efforts to accelerate

regulatory pace by removing consideration of a contaminant’s health risk reduction benefits or

occurrence may increase the cost of providing water and result in more water affordability

challenges for people served by such systems. Similarly, representatives of state drinking water

administrators have raised concerns over their current resources to enforce drinking water

regulations.136 Others have argued that the act’s current consideration of regulatory costs must be

maintained to ensure that the benefits of public health protection are maximized.137 As EPA,

states, and water systems implement drinking water regulations, congressional interest in these

issues is likely to continue.

135 U.S. Congress, House Committee on Energy and Commerce, Subcommittee on Environment and Climate Change,

There’s Something in the Water: Reforming Our Nation’s Drinking Water Standards, Testimony of Subcommittee

Ranking Member Shimkus, 116th Cong., 2nd sess., July 28, 2020.

136 Association of State Drinking Water Administrators, “ASDWA Statement on Final PFAS Drinking Water

Standards,” press release, April 2024.

137 See, for example, U.S. Congress, House Committee on Energy and Commerce, Subcommittee on Environment and

Climate Change, There’s Something in the Water: Reforming Our Nation’s Drinking Water Standards, 116th Cong., 2nd

sess., July 28, 2020, testimony from Association for State Drinking Water Administrators, and Association of

Metropolitan Water Agencies.

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Appendix A. Contaminant Candidate Lists

Table A-1. Contaminant Candidate Lists (CCLs)

CCL

Date Issued

Contaminants and Notes

CCL 1

63 FR 10274-10287

1998

60 contaminants (50 chemical contaminants and 10

microbiological contaminants)

CCL 2

70 FR 9071-9077

2005

51 contaminants (42 chemical contaminants or

contaminant groups and 9 microbiological contaminants)

CCL 3

74 FR 51850-51862

2009

116 contaminants (104 chemicals or chemical groups and

12 microbiological contaminants)

CCL 4

81 FR 81099-81114

2016

109 contaminants (97 chemicals or chemical groups and 12

microbial contaminants)

CCL 5

87 FR 68060-68085

2022

81 contaminants or groups (66 chemicals, 3 chemical

groups [PFAS, cyanotoxins, and disinfection byproducts]

and 12 microbial contaminants)

Source: Prepared by CRS from Federal Register notices.

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Appendix B. Unregulated Contaminant

Monitoring Rules

Table B-1. Unregulated Contaminant Monitoring Rules (UCMRs)

UCMR

Date Issued

Monitoring Period

Contaminants

UCMR 1

(64 FR 50556-50620)

1999

2001-2005

36 contaminants (28 chemical contaminants and

8 microbiological contaminants or contaminant

groups)a

UCMR 2

(72 FR 367-398)

2007

2008-2010

25 unregulated chemical contaminants (3

explosives, 3 acetanilide compounds and 4

associated degradation products, 6 nitrosamines,

5 flame retardants)

UCMR 3

(77 FR 26071-26101)

2012

2013-2015

30 contaminants: 29 unregulated contaminants

(27 chemical contaminants and 2 viruses) and 1

regulated contaminant (total chromium)

UCMR 4

(81 FR 92666-92692)

2016

2018-2020

30 chemical contaminants (9 cyanotoxins and 1

cyanotoxin group; 2 metals; 9 pesticides; 3

brominated haloacetic acid disinfection

byproducts groups, 3 alcohols, and 3 semivolatile

organic chemicals)

29 of these contaminants are unregulated and 1

(Haloacetic Acids 5) is regulated under the

Disinfectant Byproduct Rule

UCMR 5

(86 FR 73131-73157)

2021

2023-2025

29 PFAS and lithiumb

Source: Prepared by CRS from epa.gov and Federal Register notices.

a. For UCMR 1, EPA interpreted SDWA Section 1445(a)(2)(B)(i) to mean “that the UCMR list may contain

more than 30 contaminants, as long as monitoring is not required for more than 30 contaminants during a

five-year listing cycle” (64 FR 50566).

b. For the fifth rule, the National Defense Authorization Act for Fiscal Year 2020 (P.L. 116-92), Section 7311

directs EPA to include any PFAS (or class of PFAS) with a validated test method and excludes such

substances from counting toward the 30 contaminant limit.

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Appendix C. Regulatory Determinations

Table C-1. Regulatory Determinations (RDs)

RD Cycle

Date

Issued

Other Actions

Taken

Contaminants Evaluated

Positive

Negative

Notes

RD1

(67 FR 38222-38244)

June 3, 2002

None

Acanthamoeba, aldrin,

dieldrin,

hexachlorobutadiene,

manganese,

metribuzin,

naphthalene, sodium,

and sulfate

EPA issued guidance

on Acanthamoeba and

health advisories for

magnesium, sodium,

and sulfate

RD 2

(73 FR 44251-44261)

July 30, 2008

None

Boron, Dacthal monoacid (MTP) degradate,

Dacthal di-acid (TPA)

degradate, 1,1Dichloro-2,2-bis(pchlorophenyl)ethylene

(DDE), 1,3Dichloropropene

(Telone), 2,4Dinitrotoluene, 2,6Dinitrotoluene, s-Ethyl

propylthiocarbamate

(EPTC), Fonofos,

Terbacil, 1,1,2,2Tetrachloroethane

EPA intended to finalize

an RD for perchlorate by

December 2008a

RD 3

(81 FR 13-19)

January 4,

2016

None

Dimethoate, 1,3dinitrobenzene,

terbufos, and terbufos

sulfone

EPA delayed a final

regulatory determination

on strontium

RD 4

(86 FR 12272-12291)

March 3,

2021

PFOS

and

PFOAb

1,1-dichloroethane,

acetochlor, methyl

bromide, metolachlor,

nitrobenzene, and

RDX

EPA presented an update

on strontium and 1,4dioxane and 1,2,3trichloropropane in the

proposed RD Federal

14098-14142)

EPA issued or revised

health advisories for

boron, dacthal

degradates, 2,4dinitrotoluene, 2,6dinitrotoluene, and

1,1,2,2tetrachloroethane

Source: Prepared by CRS from epa.gov and Federal Register notices.

a. In 2011, the Administrator determined that regulation was needed for perchlorate, reversing the 2008

negative determination (76 Federal Register 7762-7767). In July 2020, the Administrator withdrew the 2011

determination to regulate perchlorate, and made a final determination not to regulate perchlorate (85

Federal Register 43990-44002). In 2023, the U.S. Court of Appeals for the D.C. Circuit vacated EPA’s 2020

withdrawal of its regulatory determination. Therefore, SDWA requires EPA to propose and finalize a

drinking water regulation for perchlorate. Following the 2023 decision, the spring 2024 Unified Regulatory

Agenda did not provide a timeline for a perchlorate proposed drinking water regulation and final rule.

b. In March 2023, EPA made an out-of-cycle determination to regulate perfluorohexane sulfonic acid (PFHxS),

perfluorobutane sulfonic acid (PFBS), hexafluoropropylene oxide dimer acid (HFPO-DA) and its ammonium

salt (also known as a GenX chemicals), and perfluorononanoic acid (PFNA), as a part of its proposed

drinking water regulation for perfluorooctanoic acid [PFOA] and perfluorooctane sulfonate [PFOS] (88

Federal Register 18638-18754).

Congressional Research Service

Regulating Contaminants Under the Safe Drinking Water Act (SDWA)

Author Information

Elena H. Humphreys

Analyst in Environmental Policy

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Congressional Research Service

R46652 · VERSION 13 · UPDATED

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