Safe Drinking Water Act (SDWA)

Key Concepts

  • The act takes a highly precautionary approach to keep our drinking water safe and reliable.
  • Water utilities are responsible for removing contaminants from water, regardless of whether the contaminants are there naturally or resulted from human activity.
  • Consumers have the right to know about the quality of their drinking water.

Historically, once people started living in close proximity in cities and towns, they started suffering epidemics of water-borne intestinal diseases such as cholera, typhoid fever, and others. With no other ready explanation, they believed these diseases came from miasmas—an undefined, evil quality of air, especially misty, dank air. So their main defense was to close their windows and drain their swamps. What they didn’t understand was that their own dense populations were the source of the problem. Human excretory wastes fouled the drinking water with disease-causing microbes and parasites. Scientific discoveries of the cause and transmission of these diseases enabled preventive approaches. The field of sanitary engineering made rapid advances in technology to appropriately handle excretory wastes. People could then have safe drinking water, uncontaminated by human wastes.

When we turn on our kitchen tap in the United States, we take for granted that the water will be clean. This doesn’t happen automatically, and it certainly doesn’t happen all over the globe. If the topic of safe drinking water seems boring, it is because you have it. Our water is safe thanks only to behind-the-scenes actions dealing with numerous threats. Before the water reaches us, someone has to treat and disinfect it. Someone also has to maintain and ensure the safety of the mains and pipes that bring the water to our homes. Moreover, the lakes, streams, and wells that provide the water must be protected against contamination.

The primary federal law that provides this protection is the Safe Drinking Water Act (SDWA).1 Its goal is to assure a safe supply of drinking water. To accomplish this goal, it requires identification, monitoring, and control of harmful contaminants before the water is piped to our homes. The act also has anti-pollution provisions for the protection of source waters, both surface and ground (subsurface) waters. The other major federal act protecting water is the Clean Water Act, covered in the previous chapter.

The SDWA is implemented by the EPA and the states. The principal regulated community consists not of polluters, but of utilities, specifically public water system (PWS). These utilities didn’t put contaminants into the water, but they are responsible for taking them out, in compliance with the standards set under this act.

public water systems (PWS)

A water utility (whether publicly or privately owned) that has at least fifteen connections or serves at least twenty-five individual customers


What Is a Public Water System (PWS)?

This statutory term is deceptive. As used here, public does not necessarily mean publicly owned. A PWS can be either municipally or privately owned. Under the SDWA, a public water system is a utility that provides water for human consumption, through a delivery system (pipes), and serves at least twenty-five customers. That means twenty-five individuals, not households. Alternatively, a water system qualifies as public if it has at least fifteen connections—for example, households, schools, and offices—regardless of the number of individual users. Thus size, not ownership, determines if a water utility is a public water system. More information about public water systems, where they get their water, and how many people they serve, is given later in this chapter.2

The EPA is not authorized to regulate private drinking water wells that have fewer than fifteen service connections and serve fewer than twenty-five persons. Nor does the act apply to bottled water, which is regulated by the Food and Drug Administration.

Regulatory Approach

Public water systems are unique among utilities in that their product is taken into the body and is essential to life.


A public water system must be certified by the state where it operates. Each state adopts its own certification standards. However, states are expected to meet at least minimum certification standards set by EPA guidelines.3

Supportive Approach

A PWS is responsible to monitor and treat or remove contaminants from the water it delivers to its customers, to ensure its safety as drinking water. How well the public water system does its job obviously has a direct impact on public health. Whereas certification and regulation of other utilities is aimed mainly at controlling unintended side effects, such as pollution or fire, a PWS is closely regulated in the performance of its basic functions.

When other utilities—or other industries in general—do not meet environmental standards, the ultimate threat is to close down their operation. But closing down a PWS would leave its customers with no water supply. Therefore, government provides substantial assistance, including financial, technological and educational assistance, to help public water systems comply with standards. Such support is especially needed by small rural water systems.


Contaminants are selected for regulation by the EPA based on the best available science.4 The intent is to focus government resources where they will do the most good in terms of protecting health. Regulation can apply to any substance capable of contaminating water, regardless of whether it is a microbial, chemical, or physical agent.

Regulatory Criteria

The Safe Drinking Water Act authorizes the EPA to regulate any contaminant that meets all three of the following criteria:

  • It may have an adverse effect on human health, and
  • The frequency and levels at which it occurs create public health concerns, and
  • Regulation “presents a meaningful opportunity for health risk reduction.”5

The first criterion embodies the precautionary nature of the act: the EPA need not wait for scientific proof, or for people to get sick, before it can regulate a suspect contaminant. The second and third criteria embody the practical nature of the act. It doesn’t matter that a substance is dangerous if nobody is exposed to it; the EPA is not authorized to regulate a contaminant that is too scarce to pose a risk. Nor is the EPA to issue regulations if they won’t do any good—for example, if there is no known technology for treating the contaminant.

How a contaminant gets into the water is not a criterion for regulation. Safe drinking water standards apply to contaminants that occur naturally as well as those that result from human activity.

Contaminant List

Contaminants that have been determined to meet the regulatory criteria are identified on a Contaminant List maintained by the EPA.6 This is the official list of regulated contaminants. The list contains close to ninety contaminants that present an actual or anticipated danger to health. These are the contaminants that a PWS must monitor and treat in compliance with the standards discussed later in this chapter. The list is not static—the act specifically provides for periodic review and update.

Contaminant List

Official list of contaminants subject to regulation under SDWA

Updating the Contaminant List

Selecting new contaminants for regulation is almost reminiscent of auditioning actors for a starring Broadway role. But here, the bad actors win.

The Candidates

Under the act, the EPA maintains a second list called the Contaminant Candidate List (CCL). These are contaminants that are not regulated, but which are likely suspects for future regulation. As of this writing, there are 116 contaminants on the candidate list. A PWS is not required to treat the listed candidates, but it is required to monitor up to thirty of them, designated by the EPA, to see if frequency and concentration might warrant closer scrutiny.

Contaminant Candidate List (CCL)

List of contaminants not regulated under SDWA, but identified by EPA as potential additions to the Contaminant List

To meet the challenge of new and worrisome contaminants, the act mandates reviews every five years to update the Contaminant Candidate List, and, if appropriate, the Contaminant List as well. (This five-year requirement does not limit the EPA’s authority to take action between reviews.)

Auditions for New Candidates

For the five-year update of the Contaminant Candidate List, the EPA enlists broad participation—asking for suggestions from scientists, including its own National Drinking Water Advisory Board, and even soliciting nominations from the public. With this input, the EPA creates a large slate of contenders. After an initial screening, the EPA focuses on the most worrisome nominees for a more detailed evaluation, based on public health risk and the likelihood of occurrence in drinking water. When it updated the CCL in 2009, the EPA started with about 7,500 contenders, from which it selected 116. The EPA’s decision to include or omit a contaminant from the Contaminate Candidate List is not subject to judicial review.

Auditions for New Regulated Contaminants

The other step of the EPA’s five-year responsibilities is to review five or more candidates to determine whether they should be added to the official Contaminant List and become regulated. The EPA, in consultation with the EPA Science Advisory Board, selects the five or more candidates that present the greatest public health concern. In making the selection of which candidates to review, particular attention is paid to at-risk subpopulations, such as infants, children, pregnant women, the elderly, and the chronically ill. The EPA evaluates the selected candidates in depth to determine whether they meet the three criteria described above—that is, adverse health effect, occurrence, and meaningful possibility of reducing risk through regulation. The conclusion of this in-depth evaluation is a formal decision by the EPA administrator, called a regulatory determination. If the EPA administrator determines that a candidate meets the criteria, it is added to the Contaminant List and the next step is to develop standards as discussed below. If the EPA administrator determines not to regulate, that is a final decision subject to judicial review.


How much of any given contaminant is allowed in the drinking water that reaches our taps? The act gives the EPA the task of setting standards to protect public health (primary standards) and public welfare (secondary standards).7

Primary Standards

The EPA sets standards for the protection of health, called National Primary Drinking Water Regulations (NPDWR) or simply primary standards. The act prescribes a two-step process to establish legally enforceable primary standards.

National Primary Drinking Water Regulations (NPDWR)

Regulations under SDWA for the protection of human health

Maximum Contaminant Level Goal (MCLG)

For each contaminant, the act directs the EPA to set the Maximum Contaminant Level Goal, meaning the ceiling needed to avoid any known or anticipated adverse health effect, with an adequate margin of safety. The act explicitly tells the EPA not to consider cost in setting the MCLG. Notice that this is a health-based standard—that is, based on the desired health outcome. Notice also that the legislative mandate is very precautionary.

Maximum Contaminant Level Goal

The level of a contaminant in drinking water that would lead to no adverse health effects

For carcinogens and microbial contaminants, it is EPA policy to set the MCLG at zero, because at least theoretically one single molecule is sufficient to cause disease, and one single microbe can divide until a sufficient number is present to cause disease. For noncarcinogenic organic chemicals, the EPA calculates the MCLG based on the reference dose (RfD)—that is, the maximum daily exposure, lifetime, without adverse health effects. The RfD is based on available epidemiological and toxicological studies and is published in the EPA’s Integrated Risk Information System (IRIS).

reference dose (RfD)

The maximum daily exposure, lifetime, shown not to cause adverse health effects

Integrated Risk Information System (IRIS)

EPA database of scientific information pertaining to risk from environmental agents

What is important to understand about the MCLG is that it is an ideal, not an enforceable limit. The ideal safe level is impossible to achieve, at least for carcinogens. So the MCLG serves as the first step to establishing the enforceable standard.

Maximum Contaminant Level (MCL)

The enforceable limit—the actual primary standard—is called the maximum contaminant level (MCL). The MCL is based on the MCLG; specifically, the EPA sets the MCL as close to the MCLG as is feasible. Under the act, feasible means the level that can be achieved with the use of the best available technology, treatment techniques, and other means, taking cost into consideration. Notice that these are technology-based standards—that is, standards based on feasibility. Notice also this is the stage where cost is considered. The EPA balances costs and benefits in setting MCLs.

maximum contaminant level (MCL)

Allowable level of a contaminant in drinking water

For carcinogens and microbial contaminants, there can be a significant difference between what is ideal (MCLG) and what is feasible (MCL). For noncarcinogenic organic chemicals, MCLG and MCL are often identical.

Treatment Techniques

For some contaminants, it’s not feasible to set a numeric MCL, for example, due to difficulty measuring actual concentration. In such cases, the EPA may prescribe a specific treatment technique An enforceable standard, prescribing a specific method of treatment that the EPA may issue if a numeric standard is deemed unfeasible that public water systems must use for that contaminant. This is an enforceable standard, just like an MCL. (See the following text box on American Water Works v. EPA.)

treatment technique

An enforceable standard, prescribing a specific method of treatment that the EPA may issue if a numeric standard is deemed unfeasible

Additional Regulatory Requirements

In addition to setting allowable limits on contaminants in drinking water, National Primary Drinking Water Standards impose further detailed responsibilities on public water systems, including:

  • Monitoring requirements (specifying location, frequency, and methodology for sampling)
  • Methodology for analyzing samples
  • Record keeping and reporting requirements (discussed later in the chapter)

The SDWA allows the EPA to prescribe a particular treatment technique as the primary drinking water standard for a contaminant if a numeric maximum contaminant level (MCL) is not economically or technologically feasible. The EPA adopted a treatment technique as the standard for lead contamination. The Natural Resources Defense Council (NRDC) challenged the EPA’s standard. The NRDC argued that lead in drinking water could be measured, so it was feasible and therefore mandatory for the EPA to adopt an MCL.

The EPA disagreed that feasible simply means measurable. The EPA interpreted feasible to mean that an MCL could be accomplished consistent with the overall public health purposes of the act. Lead gets into drinking water because it is leached from old lead pipes through which it flows. Compliance with a lead MCL would require public water systems to use aggressive corrosion control techniques. While reducing the amount of leached lead, such techniques could increase levels of other harmful contaminants, to the overall detriment of public health. The EPA concluded that an MCL was not feasible, and prescribing a particular corrosion control technique would best protect public health. The court upheld the EPA.

There was a second issue in the same case. The EPA exempted transient noncommunity public water systems from the lead standard. NRDC argued that a primary standard must apply to all public water systems, and the exemption was therefore improper. The EPA reasoned that lead poses a significant health risk only with chronic exposure. Applying the standard to a transient noncommunity system would therefore have no appreciable public health benefit, but it would be highly burdensome for these systems, many of which are quite small. The court expressed general approval of the EPA’s explanation.

Secondary Standards

The primary standards just discussed are intended to protect human health. The Safe Drinking Water Act also directs the EPA to establish National Secondary Drinking Water Standards to protect the public welfare. These apply to contaminants that can make consumers unwilling to use the water, even if it does not endanger health. For example, some contaminants cause adverse aesthetic effects (such as unpleasant taste, odor, or color) or cosmetic effects (such as discoloration of teeth or skin).

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