The Clean Water Act is regularly reviewed by Congress. You will find the Congressional Research Service's brief to the 109th Congress ("The Clean Water Act in the 109th Congress") to be extremely enlightening, not only in regard to the history of the act, but in regard to changes that Congress anticipates making in it.

Historical Timeline: The Sierra Club provides an interesting timeline for the Clean Water Act.

Introduction to CWA: To begin understanding how the Clean Water Act works, you might want to read the EPA's "Introduction to the Clean Water Act."  The entire Clean Water Act (a.k.a. Federal Water Pollution Control Act) can be accessed section-by-section at the following EPA web site. The CWA consists of six sections: (1) Title I - Research and Related Programs, (2) Title II - Grants for Construction of Treatment Works, (3) Title III - Standards and Enforcement, (4)  Title IV - Permits and Licenses, (5) Title V - General Provisions, and (6) Title VI - State Water Pollution Control Revolving Funds.

Navigable Waters: The CWA applies only to "navigable waters" so you ought to find out what that term means.

Regulating Point Sources: Whereas the Clean Air Act utilized ambient air concentration levels and then "worked backwards" to determine individual emission levels, the Clean Water Act is built around individual effluent levels built around what is called National Pollutant Discharge Elimination System or NPDES. The NPDES utilizes a system of "permits" relating to allowable levels of discharge of the following classes of pollutants:

• CONVENTIONAL POLLUTANTS - These pollutants encompass the sanitary wastes of households, businesses, and industries, to include human wastes, ground-up food from sink disposals, and laundry and bath waters.

• FECAL COLIFORM - These bacteria are found in the digestive tracts of humans and animals; their presence in water indicates the potential presence of pathogenic organisms.

• OIL & GREASE - These organic substances may include hydrocarbons, fats, oils, waxes, and high-molecular fatty acids. Oil and grease may produce sludge solids that are difficult to process.

TOXIC POLLUTANTS - These are pollutants that deemed to be particularly harmful to animal or plant life. They are primarily grouped into organics (including pesticides, solvents, polychlorinated biphenyls (PCBs), and dioxins) and metals (including lead, silver, mercury, copper, chromium, zinc, nickel, and cadmium).

• NON-CONVENTIONAL POLLUTANTS - These pollutants include any additional substances that are not conventional or toxic that may require regulation. These include nutrients such as nitrogen and phosphorus.

Pollutants that exceed the permitted level result in fines and criminal prosecution for the polluter. Under NPDES, the discharge of a pollutant is defined as "Any addition of any pollutant to navigable waters from any point source."

Basics of Water Permitting: For an  Overview to NPDES Permitting, you can go to the EPA's "Water Permitting 101" web site.

Publicly Owned Water Treatment Works (POTW): POTWs are a major source of "point-source" pollution. These are the municipal sewage treatment plants that are common to most municipalities and counties throughout the nation. These treatment facilities take raw sewage and take them through a process of "primary,"  "secondary"  and "tertiary" treatment prior to either releasing the water into a water body or stream, or prior to using the water for drinking purposes. For an overview of the sewage treatment process, you can go to the following "sewage treatment" website.

BPWTT: The Best practicable waste treatment technology (BPWTT) is defined by the United States Environmental Protection Agency as. BPWTT is "the effective technology that can treat wastewater, combined sewer overflows, and nonexcessive infiltration and inflow in publicly owned or individual wastewater treatment works" to meet applicable U.S. EPA standards for the secondary treatment of wastewater, in regard to marine discharge waivers, more stringent federal and state water quality standards in regard to so-called "alternate waste management techniques." BPWTT is based upon an evaluation of technologies included under each of the following waste treatment management techniques: (1) Biological or physical-chemical treatment and discharge to receiving waters; (2) Treatment and reuse; and (3) Land application techniques.

Industrial Point Sources: The EPA requires that "discharges of process or non-process wastewater from industrial facilities [must] be permitted either by coverage under a General Permit or an Individual Permit. Permit requirements depend on the nature and amount of products produced at a facility, and the resulting pollutants in the wastewater.  Many industrial categories have corresponding Effluent Limitations Guidelines, published in the Federal Register and subsequently added to the CFR (40 CFR Parts 405 - 471) .   These guidelines outline technology based effluent requirements for pollutants related to industrial activities by industrial category and achievable technology." 

NPDES in Statute: One of the central features of the CWA, the NPDES, is outlined in law in CFR 40 part 122, which also deals with Concentrated animal feeding operations (part 122.23), Concentrated aquatic animal production facilities (part 122.24), Aquaculture projects (part 122.25), Storm water discharges (part 122.26), Silvicultural activities (part 122.27), General permits (part 122.28), and New sources and new dischargers (part 122.29). The stature also includes the expectations for states in regard to NPDES in CFR 40 part 123. According to Section 402 of the CWA, two sets of standards are used to determine acceptable levels of discharge:

• "Water quality-based standards — designed to protect receiving bodies of water from failing to meet acceptable water quality standards.

• Technology-based standards — to ensure that, regardless of the quality of the receiving water body, a type of discharge meets a minimum level of control. Certain types of industrial discharges, such as those into sanitary sewer systems, may not require NPDES permits, but will be required to meet certain local standards, and may be subject to the Industrial Pretreatment Program. The Industrial Pretreatment Program prevents the discharge of pollutants to a Publicly Owned Treatment Work (POTW) which will interfere with the operation of the POTW or its use and disposal of municipal biosolids. In addition, the Pretreatment Program prevents the introduction of pollutants to POTWs that may pass into rivers, lakes, and streams, causing increased toxicity or other impacts. Implementation of the Pretreatment Program is outlined in 40 CFR 403.

 Discharges potentially regulated by NPDES fall into three categories:

• Conventional pollutants, such as sanitary waste or gray water.

• Toxic pollutants, which are grouped into organics (including pesticides, solvents, PCBs, and dioxins) and metals (including lead, silver, mercury, copper, chromium, zinc, nickel, and cadmium).

• Unconventional pollutants, such as nitrogen, phosphorus, or any other substance that is not conventional or toxic."

Industrial Waste Pollution Controls: According to EPA "Effluent guidelines are national standards for wastewater discharges to surface waters and publicly owned treatment works (municipal sewage treatment plants). [EPA issues] effluent guidelines for categories of existing sources and new sources under Title III of the Clean Water Act. The standards are technology-based (i.e. they are based on the performance of treatment and control technologies); they are not based on risk or impacts upon receiving waters." To get a feel for the top industrial point sources for pollution and to determine the toxins released from these sites you might want to peruse the 2005 EPA report "Preliminary 2005 Review of Prioritized Categories of Industrial Discharges." These categories covered by law are found in CFR 40 Parts 405-424, and at CFR 40 Parts 425-699, all of which can be perused online from the Code of Federal Regulations.

End of Pipe versus Cleaner Production: CWA makes use of what is called "end of pipe" technologies which are defined as "an approach to pollution control which concentrates upon effluent treatment or filtration prior to discharge into the environment, as opposed to making changes in the process giving rise to the wastes." However, this technology is considered inferior to "cleaner production"

"Best" Terminology: There are a number of terms related to the CWA that you need to become familiar with:

• Best Available Technology Economically Achievable (BATEA) 

• Best Available Control Measures (BACM)  

• Best Available Control Technology (BACT) 

• Best Available Technology (BAT)

• Best Demonstrated Available Technology (BDAT)

• Best Management Practice (BMP)

Indirect Sources: In an effort to respond to the predictable effort by some industries to avoid the restrictions of the CWA by discharging their effluent through POTWs, EPA formulated a set of "pre-treatment standards and limits." In this regard, they enforce three particular types of standards:

• Prohibited discharge limits,

• Categorical pretreatment standards; 

• Local limits

Non-Point Source Pollution: Non-point source pollution is the leading cause of water pollution in the U.S. According to the EPA, Non-Point Source pollutions is defined as " Nonpoint source (NPS) pollution, unlike pollution from industrial and sewage treatment plants, comes from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even our underground sources of drinking water. These pollutants include:

• Excess fertilizers, herbicides, and insecticides from agricultural lands and residential areas;

• Oil, grease, and toxic chemicals from urban runoff and energy production;

• Sediment from improperly managed construction sites, crop and forest lands, and eroding stream banks;

• Salt from irrigation practices and acid drainage from abandoned mines;

• Bacteria and nutrients from livestock, pet wastes, and faulty septic systems;

Atmospheric deposition and hydromodification are also sources of non-point source pollution."

Non-Point Source Pollution Control: A variety of state, tribal, federal and local agencies work together to control non-point source pollution. Pollution control has been managed in part through the awarding of so-called 310 funds or "section 319" grants (of the CWA) to states and territories to use "best management practices" clean up non-point source pollution. These and other state and federal funds have been used to combat non-point source pollution within the wide range of settings in which such pollution occurs, to include sources involving: 

• sea coasts, 

• in agricultural settings, 

• urban runoff, 

• forestry related runoff, 

• non-point source pollution emanating from boats and marinas, 

• household pollution;

• non-point source pollution impacting wetlands.

What Constitutes a "Discharge" Under the CWA: The CWA defines a discharge as "any addition of any pollutant from any point source" meaning that those seeking to avoid this requirement must assert that an effluent is either not a point source or does not add to the pollutants in the water. Numerous federal court cases have emerged in recent years in regard to the definition of "discharge." One of the most visible of these cases is South Florida Water Management District (SFWMD) v. Miccosukee Tribe of Indians (2004) in which the U.S. Supreme Court ruled that under Section 402 of the CWA a "discharge of pollutant" can only be considered to have occurred when the body of water that receives the pollutant is "meaningfully distant" from the source of the pollution. 

Designated Uses vs. Existing Uses of Water Under CWA: Section 303(c) of the CWA mandates that states create a scheme of  "uses" for every body of water within each state. Such uses are in turn referred to as "designated uses" (a.k.a. "swimmable/ fishable/ drinkable uses") or "existing uses" ("those which were occurring or have been achieved since November 28, 1978") and may apply to drinking water standards and resources, water habitats for fish and wildlife, and recreational water uses. 

Water Quality Standards Under CWA: The term "criteria" which relates to water quality under the CWA has a purposefully dual meaning (1) "Ambient criteria are part of state water quality standards in that an individual water quality standard is composed of designated uses and the water quality criteria necessary to protect those uses." (2) "water quality criteria that reflect the latest scientific knowledge of the effects on human health and aquatic life that can result from concentrations of pollutants in a water body." Another term which relates to water quality is "total maximum daily load" (TMDL). 

Interstate Efforts to Control Water Pollution: Section 103 (a) and Section 103 (b) of the CWA requires the U.S. EPA to facilitate "cooperative activities by the States" .. "relating to the prevention, reduction, and elimination of pollution." The vehicle for achieving this goal is via the use of interstate "compacts" which are developed to promote the health and quality of water that moves across state lines. Some of these compacts can be found at the U.S. Fish and Wildlife Service's web site.