Sources of water contamination include naturally occurring chemicals and minerals (arsenic, radon, uranium), local land use practices (fertilizers, pesticides, concentrated feeding operations), manufacturing processes, and sewer overflows or wastewater releases.

Infants, young children, pregnant women, the elderly, and people whose immune systems are compromised because of AIDS, chemotherapy, or transplant medications, may be especially susceptible to illness from some contaminants.

This example is a small reflection of residents of the United States remain at risk of waterborne gastrointestinal illness under current water treatment practices.

The new study of more than 700 people in California's Central Valley found that those who likely consumed contaminated private well water had a higher rate of Parkinson's.

The concurrent written opinion of Justice Anthony Kennedy defined the term more broadly, including wetlands with a "significant nexus" to traditionally-defined navigable waters.

EPA develops those standards for categories of dischargers, based on the performance of pollution control technologies without regard to the conditions of a particular receiving water body.

The intent of Congress was to create a "level playing field" by establishing a basic national discharge standard for all facilities within a category, using a "Best Available Technology."

[22] States and Native American tribes also adopt general policies pertaining to water quality standards that are subject to review and approval by the EPA.

[24] Some microbiological test procedures use microbial source tracking (MST) techniques to calculate and identify biological and chemical trends that may support new regulatory limits on pollutants.

[27] Congress, however, provided support for research, technical and financial assistance programs at the U.S. Department of Agriculture to improve runoff management practices on farms.

EPA had declined to include urban runoff and industrial stormwater discharges in its initial implementation of the NPDES program, and subsequently the agency was sued by an environmental group.

The agency began to develop regulations for stormwater permit coverage but encountered resistance from industry and municipalities, and there were additional rounds of litigation.

Every two years states must submit reports that describe water quality conditions to EPA with a complete inquiry of social and economic costs and benefits of achieving goals of the Act.

[55] This program provides grants to states, territories and Indian tribes to support demonstration projects, technology transfer, education, training, technical assistance and related activities designed to reduce nonpoint source pollution.

[69] Essentially, all discharges affecting the bottom elevation of a jurisdictional water body require a permit from the U.S. Army Corps of Engineers (USACE).

[72]: 906  Throughout the hearing process, Congressmen of every environmental persuasion repeatedly stated that the over $5 Billion invested in drainage facilities could be maintained without government regulation of any kind.

A landowner who intends to make substantial investments in acquisition or improvement of land might lawfully proceed with exempt activity, a permit not being required.

Benefits of reusing sewage sludge from use of organic and nutrient content in biosolids is valuable source in improving marginal lands and serving as supplements to fertilizers and soil conditioners.

Materials flushed in household drains through sinks, toilets and tubs are referred to as domestic wastewater and include components of soaps, shampoos, human excrement, tissues, food particles, pesticides, hazardous waste, oil and grease.

Employees in the U.S. who believe they were fired or suffered adverse action related to enforcement of the CWA may file a written complaint with the Occupational Safety and Health Administration.

[83] Congress then passed a joint resolution under the Congressional Review Act overturning the WOTUS rule,[84] but President Barack Obama vetoed the measure.

[85] On February 28, 2017, President Donald Trump signed documents directing EPA and USACE to review and rewrite the Obama administration's "Clean Water Rule," which would clarify the WOTUS definition.

[92][93] Under the administration of President Joe Biden, USACE and EPA published a revised definition of WOTUS on January 18, 2023, restoring the pre-2015 regulations on the scope of federal jurisdiction over waterways, effective March 20, 2023.

[98] Congress first addressed water pollution issues in the Rivers and Harbors Act of 1899,[99] giving the Corps the authority to regulate most kinds of obstructions to navigation, including hazards resulting from effluents.

In 1910, USACE used the act to object to a proposed sewer in New York City, but a court ruled that pollution control was a matter left to the states alone.

Speaking to the 1911 National Rivers and Harbors Congress, the chief of the Corps, William H. Bixby, suggested that modern treatment facilities and prohibitions on dumping "should either be made compulsory or at least encouraged everywhere in the United States.

[108] The Attorney General of the United States, John N. Mitchell, gave a Press Conference December 18, 1970 referencing new pollution control litigation, with particular reference to work with the new Environmental Protection Agency, and announcing the filing of a lawsuit that morning against the Jones and Laughlin Steel Corporation for discharging substantial quantities of cyanide into the Cuyahoga River near Cleveland.

[122] It is argued in a 2008 paper that the Clean Water Act has made extremely positive contributions to the environment, but is in desperate need of reform to address the pollution problems that remain.

"[125] According to a paper published by the National Bureau of Economic Research, the Clean Water Act has been one of the most controversial regulations in the history of the United States.

An analysis conducted in the 1990s provided a summary of these uncertainties, “As we approached the twenty-year anniversary of [The Clean Water Act], no comprehensive analysis was available to answer basic questions: How much cleaner are our rivers than they were two decades ago?”[126] Council of Economic Advisers chair Paul McCracken described the Clean Water Act as an “...inefficient use of national resources that would not produce balancing [of] social and economic benefits”.