Clean Water Act (CWA)

Key Concepts

  • The act protects surface waters (not groundwater) by regulating discharges from point sources, such as pipes and channels.
  • The primary approach is national technology-based standards to limit effluent discharges. Stricter standards apply to new sources. Standards also vary according to type of pollutant, type of industry, and whether the facility discharges directly to surface waters or to a treatment plant.
  • If technology-based standards do not achieve clean water, there are backup ambient water quality standards. These vary according to use (such as recreational use).
  • The Clean Water Act relies heavily on permits to enforce standards.

On June 22, 1969, the Cuyahoga River caught fire in Cleveland, Ohio. The river was a mass of oil slicks and other pollution; in its lower stretches it showed no signs of aquatic life—not even sludge worms. The Cuyahoga had burned a dozen times from 1868 to 1952. Perhaps the difference in 1969 was that every home in America could watch the flames on television. The images of a river on fire helped spur grassroots demand for environmental protection. Three years later, Congress enacted the federal Clean Water Act of 1972.

Before 1972, water pollution control was left to the individual states, and federal law just played a supportive role. The Clean Water Act changed that: it imposed more stringent antipollution regulations, and it instituted much greater federal control.

The Clean Water Act (CWA)1 is the main federal act protecting against pollution of surface waters, although there are two major water issues not included. The protection of drinking water is covered by the Safe Drinking Water Act; oil spill prevention and response are covered by the Oil Pollution Act. These two acts are discussed in later chapters.

The Clean Water Act’s chief target is industrial pollution discharged from point sources (such as pipes). The act does not directly regulate sheet runoff, notably urban storm runoff or agricultural runoff—two intractable problems. Despite the act’s shortcomings and the enormity of challenges it faces, it has succeeded in greatly improving the quality of surface waters in America. Stretches of the Cuyahoga River that were virtually dead in 1969 now support abundant aquatic life, including steelhead trout and dozens of other fish species.


This act has two names. Almost everybody calls it the Clean Water Act. But it’s also known as the Federal Water Pollution Control Act, so you may occasionally see that name.

Legislative Goal

The goal of the Clean Water Act is to restore and maintain the chemical, physical, and biological integrity of the nation’s waters. As part of this, the act seeks water quality that is fishable and swimmable. The act also seeks to eliminate discharge of pollutants. This latter goal was not met by the original deadline of 1985, nor has it been achieved even today. But progress has been made; pollutant discharges have been reduced, although not eliminated.

The Discharge Prohibition

The CWA makes it unlawful for anyone to discharge any pollutant except in compliance with the act. This key provision is commonly called the discharge prohibition, and it is the foundation of federal strategy against water pollution. To understand the scope and impact of the prohibition, and of the act itself, requires a few definitions.2

discharge prohibition

The default control measure of CWA that prohibits discharge of any pollutant not expressly allowed by a facility’s permit, or in excess of the amount allowed in the permit

What’s a Discharge?

A discharge of a pollutant refers only to a discharge from a point source, meaning a confined conveyance such as a pipe or conduit. By contrast, agricultural runoff or sheet runoff from city streets—are not discharges within the scope of the CWA even though they are potentially significant sources of water pollution.

What’s a Pollutant?

The act’s definition of pollutant is extremely broad. It includes dredged spoil, solid waste, incinerator residue, sewage, garbage, chemical wastes, and just about anything else you would expect—and a few you might not expect, such as heat, rock, and sand. It even includes munitions, such as shells or bombs from military exercises. If you accidentally drive your car off the end of a dock, that’s not a pollutant. But if you get rid of an old, rusted jalopy by pushing it off the end of a dock, that’s a pollutant.


Under CWA, almost anything placed in surface waters for purposes of disposal

What Waters Are Covered?

The Clean Water Act regulates discharges into navigable waters, but don’t be misled into thinking it only applies to waters that ships and boats can navigate. The act defines “navigable waters” to include all waters of the United States—another term that is not self-explanatory. These two terms are synonymous for purposes of the act, and they basically include

waters of the United States

Surface waters subject to regulation under CWA, including interstate waters, waters subject to the tides, waters that have some connection with interstate commerce; also called “navigable waters” even if they are not really navigable

  • Interstate waters: for example, any river or lake touching two or more states
  • Waters used in interstate commerce; for example, a river, canal, or lake that carries vessels between states
  • All waters subject to the tides—such as coastal waters of the Atlantic and Pacific Oceans

  • Intrastate waters, including wetlands, that have an adequate link to interstate commerce; for example, when fish caught there are sold in interstate commerce, or when the water body is used by interstate travelers for recreation
  • Tributaries and wetlands adjacent to any of the above

The definition of waters of the United States is important, because it defines and delimits the jurisdiction of federal agencies to regulate pollution under the Clean Water Act. After the CWA was enacted in 1972, the agencies gradually expanded their interpretation to include waters whose connection to interstate commerce was less and less obvious. That trend was abruptly interrupted in 2001, when the United States Supreme Court rejected the Army Corps of Engineers’ view that its jurisdiction under the CWA extended to an abandoned gravel pit that was seasonally filled with rainwater and had become a habitat for migrating birds.3 The question of what waters are covered by the act remains a controversial and oft-disputed issue.

For convenience, this chapter often refers to waters covered by the act simply as “waters” or “surface waters.” But keep in mind that not all intrastate water bodies qualify as “waters of the United States” and their status could be subject to debate. States generally have laws similar to the CWA and other federal environmental acts. So a water body found not to qualify as “waters of the United States” is not necessarily unprotected—it is still covered by state law.

Burden of Proof

The discharge prohibition makes it illegal to discharge any pollutant except in compliance with the act. That means in compliance with limitations on what pollutants can be discharged and in what amounts. These limits are set forth in published regulations and, what’s more, they are spelled out right in the permit issued to the individual facility. This is an effective regulatory approach, because it places the burden of proof on the discharger. In an enforcement action, it’s up to the polluter to prove that its discharge was permitted, rather than up to the agency to show that there was a violation.

Major Programs

The Clean Water Act includes several programs, of which we’ll discuss the following:

  • National Pollutant Discharge Elimination System (NPDES) regulates direct discharges to waters of the United States, mainly by industrial dischargers
  • Pretreatment program regulates industrial discharges to wastewater treatment facilities
  • Dredge and Fill Permit program: regulates the deposit of fill and dredged material to surface waters, including wetlands


The National Pollutant Discharge Elimination System (NPDES)4 is the centerpiece of the Clean Water Act. It regulates industrial facilities, as well as wastewater treatment plants, that discharge pollutants via point sources directly to surface waters. It uses a permit system that simplifies implementation and enforcement.

National Pollutant Discharge Elimination System (NPDES)

Major program of CWA that regulates discharge of pollutants to surface waters, including the requirement of a permit for any discharge

Some Definitions

The terms “pollutant,” “discharge,” and “surface waters,” as used in the CWA, were explained earlier. A few other definitions will be helpful here.

Point Source

Most commonly this is a pipe, but it can be any “confined and discrete conveyance.” Common examples of point sources are pipes, ditches, channels, and conduits, but they also include mobile conveyances such as boats.

Direct Discharger

A direct discharger is a facility that discharges, via a point source, directly into a river, lake, ocean, or other surface waters. Mostly, these are industrial and commercial facilities, and also include treatment facilities.

direct discharger

Under CWA, a point source that discharges effluent directly to surface waters

Publicly Owned Treatment Works (POTW)

These are wastewater treatment facilities, which are operated by a municipality or other local authority. After treatment, the POTW discharges the treated waste into rivers or other surface waters. Thus, POTWs are direct dischargers (by contrast, facilities that discharge their wastes via the sewer system to a POTW are called indirect dischargers).

Permit Requirement

All direct dischargers are required to have NPDES permits. It is illegal for a facility to discharge directly to surface waters without a permit.5

A facility’s NPDES permit specifies the types and amounts of pollutants the facility is allowed to discharge. It is illegal for a facility to discharge types or levels of pollutants not expressly allowed in its permit. Although effluent limits for each industrial category are published in regulations, the permit requirement facilitates enforcement of those controls. Spelling out the limits in the discharger’s individual permit eliminates later arguments.

Permits are issued by the EPA or by states with permit programs approved by the EPA. With few exceptions, each direct discharger must apply for and obtain an individual permit. In addition to specifying the pollutant limits for the facility, the permit contains other conditions. These include important requirements for monitoring its own discharges and reporting them to the EPA or the relevant state authority. Such reporting readily reveals any violations, thus aiding effective enforcement. Penalties for violations are discussed later in this chapter. The ultimate threat is revocation of a facility’s permit, without which the facility cannot legally operate.


Under the Clean Water Act, the EPA promulgates technology-based effluent limits. Technology-based means the standards are based on the EPA’s assessment of what is technologically feasible.

The act mandates various technology-based standards, which differ in their application and degree of stringency. This section will describe four major standards: best practical technology, best available technology, best conventional technology, and best available demonstrated technology. It is the EPA’s task to translate these ambiguous terms into numerical effluent limits. These limits are published in tables that fill multiple volumes. When an NPDES permit is issued, it is the permit writer’s job to select the appropriate effluent standard from those volumes, and incorporate those specific standards into the individual point-source permit.

effluent standard

A standard limiting the allowable concentration of a pollutant in discharges to surface waters

The Process of Promulgating Technology-Based Standards

The EPA looks at the actual performance of known technology and decides how low it can reasonably set effluent discharge limits. The regulations do not tell a discharger what technology it must use—just what performance it must achieve in controlling its pollutant levels.

As mentioned, the standards mandated by the act have different levels of stringency. Which standard applies depends on the type of pollutant and the type of discharger. The EPA must develop effluent limits for each standard, and for every discharger-pollutant combination. Moreover, the EPA must repeat this process for numerous different industrial categories. Because different technology-based limits apply to different industrial categories, these effluent limits are sometimes called categorical standards.

categorical standards

National effluent standards issued under the CWA, so called because different limits apply to different industrial categories

The effluent standards promulgated by the EPA are regulations with the force of law. Therefore, the EPA must follow the notice and comment procedures described in chapter 1, and the final regulations are subject to judicial review (see chapter 3).

The following sections describe the types of dischargers and pollutants, and the different standards applicable to them.

Types of Dischargers

The key distinctions among polluters are whether they are new or existing sources and whether they are direct or indirect dischargers. In addition, publicly owned treatment works (POTWs) are treated as a distinct group. Figure 4.1 is a simple diagram illustrating types of dischargers. The CWA is like the Clean Air Act, in that the term new source includes modified sources. Under both acts, a source is deemed new for purposes of an applicable regulation if it was constructed or modified after that regulation was first announced.6

new source

A source that was constructed or modified after an applicable standard was initially proposed

Figure 4.1 Types of Dischargers


As you would expect, new (or modified) sources are subject to more stringent controls than existing sources, because new sources can readily incorporate the best and latest technology. Indirect dischargers generally have easier standards than direct dischargers, because indirect discharges will be treated by a POTW.

Types of Pollutants

The CWA imposes different degrees of stringency, depending on the type of pollutant. The act addresses three categories of pollutants plus a few forbidden pollutants.

Conventional Pollutants

Conventional pollutants are the age-old public health foes, including microbial agents—the traditional targets of public sanitation and water pollution control. Their health and environmental effects are well understood. They are the types of pollutants that wastewater treatment plants can effectively treat. The act explicitly includes measurements of biological oxygen demand (BOD), an indicator of organic pollution; suspended solids; fecal coliform; and pH. The EPA has added oil and grease.7

conventional pollutants

Water pollutants, such as microbial agents and suspended solids, that are the traditional targets of public sanitation and water pollution control

Toxic Pollutants

Under the Clean Water Act, the general definition of a toxic pollutant8 is a pollutant that can cause death, disease, behavioral abnormalities, cancer, genetic mutations, reproductive malfunctions, and other severe effects in humans or other organisms. There is a more specific definition for purposes of regulation: a toxic pollutant is anything on the EPA’s official list of toxic pollutants.

toxic pollutant

Under CWA, a pollutant that can cause death, disease, behavioral abnormalities, cancer, genetic mutations, reproductive malfunctions, and other severe effects in humans or other organisms; defined more specifically by a list of toxic pollutants

There are sixty-five pollutants on the list, but many more if subcategories are counted.9 They are organic chemical substances and metals. Some of the more recognizable examples for nonscientists are arsenic, asbestos, benzene, cadmium, chloroform, DDT, lead, and mercury. The EPA issues effluent standards only for the toxic pollutants designated on the list. If an industrial facility generates a toxic pollutant not on the federal list, the relevant state effluent standard applies. Thus, a point source’s NPDES permit might include a mix of state and federal effluent standards for the various pollutants it discharges.

The EPA can add or delete pollutants from the list. In making that decision, the EPA takes into account these factors:

  • Toxicity of the pollutant
  • Its persistence or degradability
  • Whether affected organisms are usually, or potentially, present in any regulated waters
  • The importance of organisms affected
  • The nature and extent of the effect on those organisms

The act requires the EPA to review the list every three years and revise it as needed, in light of new knowledge.

Nonconventional Pollutants

This is the catch-all category. Any pollutant that is not a toxic or conventional pollutant is a nonconventional pollutant10 under the CWA. The Clean Water Act specifically lists the following as nonconventional pollutants: ammonia, chlorine, color, iron, and total phenols. The EPA may add a pollutant to the nonconventional list, if certain criteria are met:

nonconventional pollutant

Under CWA, a pollutant that is neither a conventional nor toxic pollutant; a catch-all category defined by an EPA list and including, for example, ammonia and chlorine

  • First and foremost, the EPA must determine the substance is not a toxic pollutant as defined in the act. If it is, it must be added to the toxic pollutants list rather than the nonconventional pollutants list.

  • Further, there must be sufficient data and adequate test methods to conclude that, subject to appropriate discharge limits, the pollutant will not interfere with water quality and will not pose an unacceptable risk to human health or the environment.

Forbidden Pollutants

The CWA totally bans any discharge of a few very dangerous substances:11

  • Any radiological, chemical, or biological warfare agent
  • Any high-level radioactive waste
  • Any medical waste

Technology-Based Standards

There are actually multiple technology-based standards imposed by the Clean Water Act. Each standard has its own shorthand label and, of course, its own acronym. Don’t be distracted by the profusion of labels and letters. The key point to grasp is that there are varying levels of stringency, based on type of discharger (such as direct or indirect) and type of pollutant. The following sections describe each standard. Table 4.1 provides an easy reference.

Table 4.1 Alphabet Soup: Technology-Based Effluent Standards

Standard Pollutants Sources
BPT Best Practical Technology All: Conventional, Toxic, and Nonconventional Existing direct dischargers (as of 1972)
BCT Best Conventional Technology Conventional Existing direct dischargers (after 1977)
BAT Best Available Technology Toxic and Nonconventional Existing direct dischargers (after 1977)
BADT Best Available Demonstrated Technology All: Conventional, Toxic, and Nonconventional New (and modified) direct dischargers

Best Practical Technology (BPT)

Best practical technology (BPT) is sort of a baseline effluent standard for existing sources discharging directly to surface waters. When enacted in 1972, BPT was the first standard Congress intended to be met, in a plan to reduce effluent discharges over time, with the ultimate goal of eliminating them. To reach that goal, Congress set 1977 as a deadline to achieve BPT, and 1989 to achieve the more stringent standards (BCT and BAT) discussed in the following sections. The 1977 deadline wasn’t met. But BPT effluent limits remain on the books, forming a sort of baseline, and frequently adopted by reference in the volumes of BCT and BAT standards.

best practical technology (BPT)

First technology-based standard for effluent reduction under CWA

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