Safe Drinking Water Act, MCLs & Drinking Water Regulatory Framework

The Safe Drinking Water Act, commonly called the SDWA, is the primary federal law governing public drinking water in the United States. It establishes the framework EPA uses to protect drinking water quality and gives federal, state, tribal, and local drinking-water programs defined responsibilities for implementing and enforcing drinking-water requirements.

Water operators do not need to memorize every section of federal law, but they should understand how drinking-water regulations are organized, what different regulatory terms mean, and how those requirements affect treatment, monitoring, reporting, and daily operation.

What Is the Safe Drinking Water Act?

Congress enacted the Safe Drinking Water Act in 1974. Major amendments followed in 1986 and 1996.

The law authorizes the U.S. Environmental Protection Agency, or EPA, to establish national drinking-water requirements designed to protect public health from naturally occurring and human-made contaminants.

The SDWA framework addresses more than treatment alone. It affects source-water protection, contaminant standards, treatment techniques, monitoring, reporting, public notification, operator responsibilities, and enforcement.

Who Must Comply with Federal Drinking-Water Rules?

National Primary Drinking Water Regulations apply to public water systems, commonly abbreviated PWS.

In general, a public water system provides water for human consumption and has at least:

• 15 service connections; or
• 25 people served for at least 60 days during the year.

Small private wells serving individual residences generally do not fall under the federal public-water-system regulatory structure unless they meet the definition of a public water system.

Public Water System Categories

Public water systems are commonly divided into three major types.

Community Water System

A community water system serves year-round residents.

Examples include:

• cities;
• towns;
• subdivisions;
• mobile-home communities.

Non-Transient Non-Community Water System

A non-transient non-community water system regularly serves many of the same people for an extended period but does not primarily serve their residences.

Examples can include:

• schools;
• factories;
• office buildings;
• hospitals with their own water supplies.

Transient Non-Community Water System

A transient non-community system serves people who do not generally remain at the location for long periods.

Examples include:

• campgrounds;
• highway rest areas;
• some restaurants or service facilities with independent water supplies.

Why System Type Matters

Not every drinking-water rule applies identically to every public water system.

Requirements can depend on factors such as:

• system type;
• population served;
• water source;
• treatment process;
• previous monitoring results;
• applicable contaminant rule.

An operator should therefore follow the requirements that apply to the specific system rather than assuming that every public water system has the same monitoring schedule or treatment obligations.

National Primary Drinking Water Regulations

EPA establishes National Primary Drinking Water Regulations, commonly abbreviated NPDWRs.

Primary regulations are health-based and enforceable.

They can establish requirements such as:

• Maximum Contaminant Levels;
• treatment techniques;
• maximum residual disinfectant levels;
• monitoring requirements;
• analytical requirements;
• reporting requirements;
• public-notification requirements.

Maximum Contaminant Level Goal

A Maximum Contaminant Level Goal, or MCLG, is a public-health goal.

The MCLG represents a contaminant level below which there is no known or expected risk to health, allowing for a margin of safety.

An MCLG is:

not federally enforceable.

This distinction is important. The MCLG helps establish the health objective, but compliance is normally determined using the enforceable requirement established by the regulation.

Maximum Contaminant Level

A Maximum Contaminant Level, or MCL, is the highest level of a regulated contaminant allowed in drinking water under the applicable federal regulation.

An MCL is:

enforceable.

EPA generally sets an MCL as close to the MCLG as feasible while considering available treatment technology and other statutory factors.

MCLG Versus MCL

For exam purposes, remember the basic distinction:

• MCLG: health-based goal and not enforceable;
• MCL: regulatory limit and enforceable.

Example of the Difference

Suppose a contaminant has a health-based goal below the concentration that can reliably be achieved and measured using feasible technology.

The MCLG can remain the health objective while the enforceable MCL is established at a concentration that can be achieved under the regulatory standard-setting process.

An operator must comply with the enforceable requirement, not simply know the health goal.

Treatment Techniques

EPA does not regulate every contaminant using a numerical MCL.

When establishing a reliable numerical contaminant limit is not the appropriate regulatory approach, EPA can require a treatment technique.

A treatment technique is an enforceable requirement involving a treatment process, procedure, or performance level intended to control a contaminant or public-health risk.

Examples of Treatment-Technique Rules

Federal drinking-water requirements that use important treatment-technique concepts include:

• Surface Water Treatment Rules;
• Lead and Copper Rule requirements;
• certain microbial-control requirements.

The key exam point is that a treatment technique is not optional guidance. When applicable, it is an enforceable regulatory requirement.

Maximum Residual Disinfectant Level

Some drinking-water regulations establish a Maximum Residual Disinfectant Level, or MRDL.

An MRDL is the maximum level of a disinfectant allowed in drinking water under the applicable regulation, subject to regulatory provisions and exceptions.

Disinfectants are necessary to control microbial risk, but excessive disinfectant exposure can also create health concerns and contribute to disinfection byproducts.

Maximum Residual Disinfectant Level Goal

A Maximum Residual Disinfectant Level Goal, or MRDLG, is the health-based goal associated with a disinfectant.

Like an MCLG, an MRDLG is not the enforceable compliance limit.

For exam purposes:

• MRDLG: non-enforceable health goal;
• MRDL: enforceable disinfectant limit under the applicable rule.

National Secondary Drinking Water Regulations

EPA also establishes National Secondary Drinking Water Regulations.

Secondary standards primarily address aesthetic or cosmetic effects rather than the health-based protection provided by primary standards.

Examples of concerns addressed by secondary standards can include:

• taste;
• odor;
• color;
• staining;
• corrosivity;
• other aesthetic water-quality characteristics.

Federal secondary standards are generally non-enforceable guidelines, although states can adopt their own enforceable requirements.

Primary Versus Secondary Standards

A useful distinction is:

• primary drinking-water standards protect public health and are federally enforceable;
• secondary drinking-water standards generally address aesthetic or cosmetic water-quality concerns and are normally not federally enforceable.

Do Not Assume Secondary Means Unimportant

Although secondary standards generally are not federal health-based compliance limits, the conditions they address can still create significant operational and customer-service problems.

Examples include:

• iron staining;
• manganese discoloration;
• taste and odor;
• corrosion;
• high total dissolved solids.

A state can also establish enforceable requirements that go beyond the federal secondary framework.

State Primacy

The Safe Drinking Water Act allows qualifying states, territories, and tribes to receive primary enforcement responsibility for the Public Water System Supervision program.

This authority is commonly called:

primacy.

Requirements for Primacy

To obtain and maintain primacy, the responsible agency must meet federal requirements.

Important elements include:

• drinking-water regulations no less stringent than federal National Primary Drinking Water Regulations;
• adequate enforcement authority;
• recordkeeping and reporting capability;
• appropriate variance and exemption procedures when applicable;
• emergency planning capability.

Why Primacy Matters to Operators

An operator often works primarily with the state or other primacy agency rather than communicating directly with EPA for routine compliance matters.

The primacy agency can:

• implement federal requirements;
• adopt state-specific requirements;
• review monitoring data;
• conduct inspections;
• issue compliance directions;
• take enforcement action.

Federal Requirements Are the Regulatory Floor

A primacy state must implement requirements that are no less stringent than applicable federal primary drinking-water regulations.

A state can impose additional or more stringent requirements.

Therefore, an operator preparing for a state certification exam must understand both:

• the federal regulatory framework; and
• the applicable state implementation requirements.

Operator Responsibility

Operators are not expected to function as attorneys or regulatory program administrators, but they are responsible for operating the system in a manner consistent with applicable requirements.

Operational compliance can require the operator to understand:

• required treatment processes;
• critical operating limits;
• sampling locations;
• sampling frequency;
• monitoring equipment;
• recordkeeping requirements;
• reporting deadlines;
• response to abnormal results.

Compliance Is More Than Producing Clear Water

Water that looks clear is not necessarily compliant or safe.

Many regulated contaminants:

• have no visible color;
• have no noticeable odor;
• have no obvious taste;
• cannot be evaluated without analytical testing.

Regulatory compliance therefore depends on treatment, monitoring, analytical data, documentation, and required reporting.

Monitoring Is Part of Compliance

Meeting a treatment target does not eliminate monitoring obligations.

A public water system must perform monitoring required by the applicable rule and approved monitoring framework.

Failure to collect a required sample can create a compliance problem even when there is no evidence that contaminant concentrations exceeded an MCL.

Reporting Is Part of Compliance

Collecting a valid sample is only one step.

Results and other required information must also be reported according to applicable regulatory requirements.

Operators should understand that compliance can involve several separate questions:

• Was the sample collected?
• Was it collected from the correct location?
• Was it collected at the required time?
• Was an approved analytical method used?
• Was the result reported correctly?
• Was required follow-up completed?

Recordkeeping

Public water systems must maintain records required by applicable drinking-water regulations.

Records help demonstrate:

• treatment performance;
• monitoring compliance;
• corrective actions;
• equipment operation;
• regulatory reporting.

Violations Are Not All the Same

A drinking-water violation does not always mean the same thing.

Depending on the rule, violations can involve:

• exceeding an MCL;
• failing a treatment-technique requirement;
• exceeding an applicable MRDL;
• failure to monitor;
• failure to report;
• failure to provide required public notice.

The required response depends on the specific rule and violation.

Do Not Guess the Required Response

If an abnormal result or operational condition occurs, the operator should determine which regulatory requirement applies and follow the facility's compliance procedures.

A response can involve:

• confirmation or repeat sampling;
• operational adjustment;
• additional monitoring;
• notification of management;
• notification of the primacy agency;
• public notification.

The exact response should come from the applicable rule and state implementation requirements.

Public Notification

The federal drinking-water framework requires public notification for specified drinking-water violations and situations.

Notification urgency depends on the type and seriousness of the condition.

The detailed Tier 1, Tier 2, and Tier 3 public-notification framework is covered separately in this Study Guide.

Consumer Confidence Reports

Community water systems are subject to Consumer Confidence Report requirements.

These reports communicate drinking-water information to customers, including information required by the applicable federal rule.

Detailed CCR requirements are covered separately in this Study Guide.

Major Federal Drinking-Water Rule Families

An operator may encounter several major federal rule families.

Examples include:

• Revised Total Coliform Rule;
• Ground Water Rule;
• Surface Water Treatment Rules;
• Lead and Copper Rule;
• Disinfectants and Disinfection Byproducts Rules;
• chemical contaminant rules;
• radionuclide requirements;
• Public Notification Rule;
• Consumer Confidence Report requirements.

The purpose of this article is to establish the regulatory framework. The detailed requirements of the major rule families are covered in the following articles.

MCL Compliance Is Not the Same as Treatment Performance

An operator should distinguish regulatory compliance values from operational process-control targets.

For example, an operator may maintain an internal treatment target that is more conservative than the regulatory limit.

This provides operating margin and can help prevent a compliance problem before one occurs.

Example: Internal Turbidity Target

A treatment plant may choose to operate filtration well below the maximum regulatory performance threshold.

The lower internal target is an operational control point.

The regulatory requirement remains the enforceable compliance standard.

Operators should know which numbers are:

• regulatory limits;
• permit or state requirements;
• facility action levels;
• normal process-control targets.

Example: MCLG and MCL

An operator is asked which value is enforceable.

The correct regulatory concept is:

MCL is enforceable. MCLG is a non-enforceable health goal.

Example: Treatment Technique

An operator is asked whether a treatment technique is merely EPA guidance.

The correct answer is:

No. An applicable treatment technique is an enforceable regulatory requirement.

Example: Primacy

An operator is asked why a state drinking-water agency can enforce federal-style drinking-water requirements.

The state may have EPA-approved primacy and therefore primary responsibility for implementing and enforcing the Public Water System Supervision program within the state.

Example: State Rule Is More Stringent

Suppose the federal rule establishes one minimum requirement and the primacy state adopts a stricter requirement.

The operator must follow the applicable state requirement.

The federal rule should not be treated as permission to ignore a more stringent state requirement.

Common Exam Mistakes

• Confusing an MCLG with an enforceable MCL.
• Assuming a treatment technique is optional guidance.
• Confusing an MRDL with an MRDLG.
• Assuming federal secondary standards are the same as primary health-based standards.
• Assuming every public water system has identical monitoring requirements.
• Ignoring state requirements because a federal rule exists.
• Assuming regulatory compliance depends only on finished-water appearance.
• Forgetting that monitoring, reporting, and recordkeeping can themselves be compliance requirements.

A Practical Regulatory Review for Operators

1. Identify the type of public water system.
2. Identify the source-water type.
3. Identify applicable federal and state rules.
4. Determine the enforceable MCL, treatment technique, or other standard.
5. Confirm required monitoring locations and frequencies.
6. Verify treatment and operational controls.
7. Review analytical results.
8. Complete required reporting and records.
9. Respond promptly to abnormal results or violations.
10. Follow required public-notification procedures when applicable.

What to Remember for the Exam

• The Safe Drinking Water Act is the primary federal law governing public drinking-water systems.
• SDWA was enacted in 1974 and significantly amended in 1986 and 1996.
• EPA establishes National Primary Drinking Water Regulations under the SDWA framework.
• A public water system generally has at least 15 service connections or serves at least 25 people for at least 60 days per year.
• MCLG means Maximum Contaminant Level Goal and is not enforceable.
• MCL means Maximum Contaminant Level and is enforceable.
• A treatment technique is an enforceable process or performance requirement.
• MRDL is an enforceable disinfectant limit under the applicable rule.
• MRDLG is a non-enforceable health goal.
• Primary standards are health-based and enforceable.
• Federal secondary standards generally address aesthetic or cosmetic water-quality concerns and are usually non-enforceable federally.
• Primacy means primary enforcement responsibility for the public-water-system program.
• Primacy agencies must implement drinking-water requirements that are no less stringent than applicable federal primary standards.
• States can establish requirements more stringent than the federal minimum.
• Compliance includes treatment, monitoring, reporting, recordkeeping, and required corrective actions.
• A failure to monitor or report can be a regulatory violation even without a confirmed MCL exceedance.
• Operators must distinguish regulatory limits from internal process-control targets.
• Detailed microbial, surface-water, lead and copper, DBP, monitoring, public-notification, and CCR requirements are addressed by separate drinking-water rules.