The Safe Drinking Water Act (SDWA): Summary and Impact

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The Safe Drinking Water Act (SDWA) is a law that protects the quality of drinking water in the United States. Passed by Congress in 1974 and amended in 1986 and 1996, the SDWA applies to every public water system in the country, as well as their sources in rivers, lakes, reservoirs, springs, and groundwater wells (whether they are publicly or privately owned).

The United States Environmental Protection Agency (EPA) works together with individual state governments to ensure that standards are met within local water systems, protecting communities from both naturally occurring and human-made contaminants. According to the EPA, "92% of the U.S. population with water supplied by community systems has access to drinking water that meets all health-based standards year round."

During the late 1960s, media reports of water pollution and waterborne disease outbreaks led the government to conduct several research studies to identify issues surrounding the country's water supply. In particular, a study conducted by the Public Health Service in 1970 discovered that 41% of the 969 public water systems investigated had been delivering inferior or potentially dangerous water to citizens. Seeing as the project only surveyed 5% of the national total, it was clear that the country needed to seriously rethink its water technologies, knowledge, and policies. These findings, among others, inspired Congress to pass the Safe Drinking Water Act.

When it comes to the United States, improperly disposed chemicals, animal waste, pesticides, and naturally occurring substances can all contaminate drinking water. Even clean water that runs through an improperly maintained distribution system or that isn’t treated correctly can pose health risks. The SDWA established minimum standards to protect the country’s tap water and required public water system owners and operators to comply. While the original SDWA focused primarily on treatment, amendments in 1996 recognized water protection from the source, providing operator training, funding for improvements, and accessible public information about source water. The 1996 amendments also required the EPA to consider the best available peer reviewed science in its SDWA decisions.

Summary of the Law

The SDWA not only protects source water, but also its treatment and distribution. Water systems are responsible for treating and testing their water to ensure contaminants in the tap don't exceed SDWA standards, reporting results to the state department. What’s more, if a water system isn’t meeting standards, the water supplier is required to notify its customers as well as the EPA. Some water systems also prepare annual reports for customers and rely on citizen advisory committees and civic leaders to protect resources.

The EPA generally uses a three-step process to set its water standards. First, it identifies contaminants that pose a risk to public health and submits them for further study. Second, the EPA determines a maximum contaminant level goal, which is essentially the concentration level of a specific pollutant below any known or expected risk to health. Then, the agency officially specifies the maximum permissible level of each contaminant.

Maximum Contaminant Level Goals

Sources for water contaminations can include naturally occurring chemicals and minerals (such as arsenic), land use practices (such as fertilizers or pesticides), manufacturing waste, and sewer overflows.

The maximum contaminant level goal (MCLG) refers to the level of a contaminant in water below which there is currently no known or expected risk to human health. It provides a margin of safety to public health goals but isn’t enforceable.

Maximum Contaminant Levels

Safety of drinking water concept
Illustration showing cysts of Giardia intestinalis protozoan, the causative agent of giardiasis and diarrhea due to contaminated drinking water. Dr_Microbe / Getty Images

The EPA has set limits and water testing schedules on over 90 contaminants to protect human health, giving individual states the responsibility to set and enforce its own drinking water standards as long as those standards are equal to or exceed the EPA’s national standards. If there isn’t a reliable or “economic” method to detect the contaminants, the EPA instead specifies a “treatment technique” that describes how to treat the water to remove contaminants instead.

The maximum contaminant level (MCL) is the highest level of contaminant allowed in drinking water, which is typically set close to the MCLG. However, unlike MCLGs, MCLs are enforceable by the EPA.

Contaminants are categorized into the following groups:

Microorganisms: Defined as any microscopic organism, such as a bacterium, virus, or fungus, microorganisms are one of the most common contaminants threatening drinking water safety. Giardia lamblia, a tiny parasite that spreads easily through accidentally swallowing contaminated water, can also spread from person to person and causes gastrointestinal illness. The maximum contaminant level goal for Giardia lamblia is zero, while the MCL is 99.99% removal.

Disinfectants: Disinfectants refer to the chemicals designed to destroy microorganisms, such as chloramines, which are formed when ammonia is added to chlorine to treat drinking water. Too much exposure can cause eye and nose irritation, stomach discomfort, or anemia. The MCLG and the MCL are both 4 milligrams per liter.

Disinfection Byproducts: Disinfection byproducts form when disinfectants react with compounds that occur naturally in the water. An example of this is chlorite, which can cause anemia (especially in infants and young children) and nervous system effects. The MCLG is 0.8 milligrams per liter and the MCL is 1 milligram per liter.

Inorganic Chemicals: Inorganic contaminants can include arsenic and iron. Arsenic can cause skin damage or circulatory system problems and even increased risk of cancer. It’s created by natural erosion as well as runoff from orchards or runoff waste from glass or electronic production. The MCLG is zero, while the MCL is 0.010 milligrams per liter.

Organic Chemicals: Organic pollution can happen when an excess of organic matter enters the water, such as manure or sewage. Dichloromethane, in particular, can lead to liver problems or increased risk of cancer, and occurs from drug or chemical factory runoff. The MCLG is zero and the MCL is 0.005 milligrams per liter.

Radionuclides: Radionuclides emit excess nuclear energy or radiation. Uranium, for example, happens when natural deposits erode, and can increase cancer risk or kidney toxicity. The MCLG is zero and the MCL is 30 micrograms per liter.

Secondary Standards and Health Advisories 

Dirty brown water running into a sink
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In addition to the maximum contaminant levels, the EPA also establishes non-mandatory national secondary drinking water regulations for 15 contaminants. While the secondary regulations aren’t necessarily considered a health risk, they’re recommended to manage more aesthetic qualities to drinking water — such as taste, color, or odor. Although they aren’t enforced, the EPA requires special notice when specific elements, such as fluoride (which can cause tooth discoloration), exceed certain levels.

Why include these contaminants if they don’t pose health risks? The EPA believes that when they’re present above standard levels, the contaminants can compel people to stop using water from the public water system, even if it’s safe to drink.


The 1996 amendment requires that the public be provided with an annual national compliance report summarizing violations to public water systems. In response, the EPA and primary agencies initiate enforcement actions within their jurisdictions. During 2016, there were 51,573 public water systems in the United State that had at least one violation.

Underground Sources of Water

Groundwater, or underground water sources, are found within cracks and spaces in soil, sand, and rock. Groundwater occurs when rain seeps into the ground rather than landing on a body of water or running off into a nearby body of water. Eventually, groundwater resurfaces when it is withdrawn from a well or spring, seeps out of an earth cutaway, or intersects with a nearby waterbody.

Groundwater can sometimes become contaminated through natural or human activities, for example by accidental industrial waste spills, septic systems, injection wells, or contaminated irrigation water. Since groundwater can be especially difficult or expensive to clean up if it becomes contaminated, the EPA implemented a Ground Water Rule in 2006 to protect public water systems from disease-causing microorganisms.

Current Status

Many residents of developed countries don’t think twice when they turn on the tap to wash their hands or take a shower — but clean, healthy water is a real luxury compared to the rest of the world. In reality, 1 in 3 people don’t have access to safe drinking water globally. According to UNICEF and the World Health Organization, there are about 2.2 billion people around the world who don’t have safely managed drinking water services and a total of 144 million people who drink untreated surface water.

House Committee Holds Hearing On Flint Water Contamination
Flint residents hold bottles full of contaminated water during a news conference after attending a House Oversight and Government Reform Committee hearing on the Flint, Michigan, water crisis. Mark Wilson / Getty Images

In 2014, a city water supply switch in Flint, Michigan, caused a massive public health crisis and subsequent federal state of emergency. Almost immediately after the city began drawing its water from the Flint River (reportedly as a money-saving move), residents began complaining about health issues like rashes and hair loss, as well as aesthetic concerns like water taste and smell. A series of reports, including a few conducted by the Michigan Civil Rights Commission argued that systemic racism and environmental injustice contributed to the crisis; the reports were supported by the fact that almost 39% of Flint residents live below the poverty line and 54% of residents are Black.

There have been other studies showing that Safe Drinking Water Act violations are greater in low-income communities with higher populations of minorities. A 2017 study by the American Water Works Association found that moving from a community with 0% Hispanic population to a community with 80% Hispanic population and 40% poverty increased the predicted number of violations from 0.09 to 0.17 per year; the average number of annual health violations in the United States overall is 0.19.

The EPA continues to work alongside federal, state, and private regulatory partners to ensure that the regulated community adheres to laws that protect human health and the environment with the Clean Water Act compliance monitoring program

View Article Sources
  1. McCabe, Leland J., et al. “Survey of Community Water Supply Systems.” Journal (American Water Works Association), vol. 62, no. 11, 1970, pp. 670–687.

  2. UNICEF and WHO. "Progress on Drinking Water, Sanitation and Hygiene." 2019.

  3. "Quick Facts: Flint, Michigan." U.S. Census Bureau.

  4. Switzer, David, and Manuel P. Teodoro. "The Color Of Drinking Water: Class, Race, Ethnicity, And Safe Drinking Water Act Compliance." Journal - American Water Works Association, vol. 109, 2017, pp. 40-45., doi:10.5942/jawwa.2017.109.0128