Contaminants Regulated by the U.S. Environmental Protection Agency and their Health Effects


What role does the U.S. Environmental Protection Agency play in
drinking water regulation?

The U.S. Environmental Protection Agency (US EPA) plays an important role in protecting human health and the environment. The agency is influential in developing regulations, in the United States, based around health and environmental protection. They also enforce each of the regulations that they have implemented. As of May 2009, the US EPA has put into action almost 90 primary and 15 secondary drinking water regulations. Primary regulations are enforceable standards. On the other hand, secondary regulations are recommendations for drinking water contaminant levels. Secondary regulations are not required to be abided by; these are in place to reduce or eliminate cosmetic and aesthetic effects of drinking water contaminants.

What are water contaminants and where do they come from?

A water contaminant is a substance which is found in water that has the potential to pose a risk to public health at certain levels. Some contaminants occur naturally in the environment and seep into water sources through erosion. Unfortunately, many of the contaminants found in water are a result of human activities. The industrial wastes from factories, refineries, mines and mills all contain harmful substances which can contaminate water sources. Agriculture also plays a part in the contamination of water. Many chemicals used in agriculture can leach into the water system. In terms of microbiological contaminants, many of them are found in human and animal biological waste. For this reason, water sources located too close to agricultural livestock may also become contaminated.

How does the US EPA determine which water contaminants to regulate?

Possible water contaminants are listed by the US EPA on a Contaminant Candidate List (CCL). This list is a requirement of the Safe Drinking Water Act (SDWA), and it is compiled every five years. This list is assembled in a few key steps. A very broad list of possible contaminants is created and then narrowed down based on the probability of occurrence in water, known or potential health effects, and expert advice. Once created, the CCL is used to determine which contaminants pose a health risk and should become regulated. The SDWA requires that five contaminants are selected from the list to be further analyzed for potential regulation. There are three criteria used by the US EPA to determine if a contaminant should be regulated. First, the contaminant in question may pose a potential health risk. Second, the contaminant has been found in water and is believed to contaminate water at a frequency that poses a danger to public health. Third, regulating the contaminant is believed to provide a reduction in public health risk. Once these three criteria are met, further research on the contaminant can be carried out to determine the maximum contaminant level (MCL) permitted in drinking water. The MCL is the highest concentration of a particular contaminant in drinking water that is not believed to pose a public health risk.

What types of contaminants are regulated?

The primary and secondary regulations cover disinfectants, disinfectant byproducts, inorganic and organic chemicals and microorganisms including bacteria, viruses, and protozoa. These organisms need to be regulated because many of them are known to cause illness, mainly gastrointestinal problems. Disinfectants are commonly used in the treatment process to kill microorganisms that may be present in the water. The levels of these disinfectants in water need to be regulated because they can have harmful effects on human health or go through chemical reactions in the water to create byproducts. These byproducts can be harmful if consumed. Inorganic and organic chemicals must be reduced or eliminated from drinking water as most are unsuitable for human consumption.

Tables of all the contaminants regulated by the US EPA can be found at the end of this fact sheet. This includes both the primary and secondary drinking water regulations. Also listed are the health problems associated with long-term exposure and the source of water contamination. The majority of the data in this table was taken directly from the US EPA website.

What health risks do these contaminants pose?

Different contaminants cause different problems which can be separated into two categories, acute and chronic. Acute health effects are more immediate. These occur within hours or days of ingesting the contaminated water. A certain level of contamination is required to cause acute health effects and this varies depending on the contaminant involved. Although individuals may become ill from acute contamination, most people recover fully. However, people who already have a compromised immune system can become severely ill and, in extreme cases, the illness may result in death.

Chronic health effects are those seen after many years of ingesting contaminated water. Many different water contaminants, consumed over time, can lead to an increased risk of cancer. The types of cancer vary considerably, but most are associated with chemical or radiological contaminants. There are many other severe health problems associated with long-term exposure to water contaminants. Liver and kidney problems are relatively common, along with reproductive difficulties. There are also quite a few contaminants that cause problems with the nervous system. These are just a few examples of health effects associated with water contamination; the tables at the end of this fact sheet show the contaminants and their effects in more detail.

Why are some contaminants regulated by the US EPA, but not Health Canada, and vice versa?

Health Canada’s guidelines vary slightly from that of the US EPA. There can be many reasons for this discrepancy. First and foremost, some contaminants are only found in certain regions. If there is little risk of water being contaminated with a particular substance, there is no need to regulate it. Some contaminants are not given a numerical guideline by Health Canada because the levels normally found in Canadian water are much lower than they believe would be necessary to cause health problems. In some cases there may not yet be sufficient research on a contaminant to support the implementation of a guideline. Health Canada follows similar criteria to the US EPA and once adequate research is done, a Canadian Guideline will be put in place if necessary. It is also important to note that some contaminants regulated by Health Canada are not regulated by the US EPA. The same reasons apply to this situation. Note that contaminants have regulations in the U.S. and guidelines in Canada. This means that the limits are not legally enforceable in Canada. For more information, please read the fact sheet: What is the Purpose of Drinking Water Quality Guidelines/Regulations?

Regulated Contaminants

Water Contaminants
Water Contaminants Continued
Disinfection Byproducts



See the High School Operation Water Drop Total Chlorine Lesson Plan to read more about Chlorine.

Inorganic Chemicals

Inorganic Chemicals
Inorganic Chemicals Continued

See the High School Operation Water Drop Arsenic lesson plan to learn more about arsenic.

See the High School Operation Water Drop Copper lesson plan to learn more about copper.

See the High School Operation Water Drop Nitrate lesson plan to learn more about nitrate.

Inorganic Contaminants

Organic Chemicals

Organic Chemicals
Organic Chemicals Continued
More Organic Chemicals
Even More Organic Chemicals
Still More Organic Chemicals



The Safe Drinking Water Foundation has educational programs that can supplement the information found in this fact sheet. Operation Water Drop looks at the chemical contaminants that are found in water; it is designed for a science class. Operation Water Flow looks at how water is used, where it comes from and how much it costs; it has lessons that are designed for Social Studies, Math, Biology, Chemistry and Science classes. Operation Water Spirit presents a First Nations perspective of water and the surrounding issues; it is designed for Native Studies or Social Studies classes. Operation Water Health looks at common health issues surrounding drinking water in Canada and around the world and is designed for a Health, Science and Social Studies collaboration. Operation Water Pollution focuses on how water pollution occurs and how it is cleaned up and has been designed for a Science and Social Studies collaboration. To access more information on these and other educational activities, as well as additional fact sheets, visit the Safe Drinking Water Foundation website at


U.S. Environmental Protection Agency, Drinking Water Contaminants

Health Canada