An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Report on the Environment

Drinking Water

What are the trends in the quality of drinking water and their effects on human health?

Importance of Drinking Water

The average American consumes 1 to 2 liters of drinking water per day. Virtually all drinking water in the United States comes from fresh surface waters and ground water aquifers.

Top of Page

Drinking Water Quality

Surface waters and aquifers can be contaminated by various chemicals, microbes, and radionuclides. Disinfection of drinking water has dramatically reduced the prevalence of waterborne diseases (such as typhoid, cholera, and hepatitis) in the United States. Other processes may also be used to treat drinking water depending on the characteristics of and contaminants in the source water.

Common sources of drinking water contaminants include:

  • Industry and agriculture. Organic solvents, petroleum products, and heavy metals from disposal sites or storage facilities can migrate into aquifers. Pesticides and fertilizers can be carried into lakes and streams by rainfall runoff or snowmelt, or can percolate into aquifers.
  • Human and animal waste. Human wastes from sewage and septic systems can carry harmful microbes into drinking water sources, as can wastes from animal feedlots and wildlife. Major contaminants include Giardia, Cryptosporidium, and E. coli.
  • Treatment and distribution. While treatment can remove many contaminants, it can also leave behind byproducts (such as trihalomethanes) that may themselves be harmful. Water can also become contaminated after it enters the distribution system, from a breach in the piping system or from corrosion of plumbing materials made from lead or copper.
  • Natural sources. Some ground water is unsuitable for drinking because the local underground conditions include high levels of certain contaminants. For example, as ground water travels through rock and soil, it can pick up naturally occurring arsenic, other heavy metals, or radionuclides.

Top of Page

Effects on Human Health

If drinking water contains unsafe levels of contaminants, it can cause health effects, such as gastrointestinal illnesses, nervous system or reproductive effects, and chronic diseases such as cancer. Factors that can influence whether a contaminant will lead to health effects include the type of contaminant, its concentration in the water, individual susceptibility, the amount of water consumed, and the duration of exposure.

  • Health effects of chemical exposure. Chemical exposure through drinking water can lead to a variety of short- and long-term health effects. Exposure to high doses of chemicals can lead to skin discoloration or more severe problems such as nervous system or organ damage and developmental or reproductive effects. Exposure to lower doses over long periods of time can lead to chronic, longer-term conditions such as cancer. The effects of some drinking water contaminants are not yet well understood.
  • Health effects of consuming water with disease-causing microbes. Most life-threatening waterborne diseases caused by microbes (such as typhoid fever or cholera) are rare in the United States today. The more common illnesses caused by viruses, bacteria, and parasites can result in stomach pain, vomiting, diarrhea, headache, fever, and kidney failure. Infectious diseases such as hepatitis can also occur. Hepatitis may be severe in people with weakened immune systems (e.g., infants and the elderly) and sometimes fatal in people with severely compromised immune systems (e.g., cancer and AIDS patients).

Top of Page

ROE Indicators

The ROE presents one Drinking Water indicator based on violations of drinking water standards that states report to EPA. This indicator covers community water systems, which served 94 percent of the U.S. population in 2017.

The ROE does not provide information about the quality of drinking water from private wells, which the federal government does not monitor. It also does not discuss the quality of bottled water, which is regulated separately by the Food and Drug Administration.

The ROE does not yet include any indicators related to the connection between drinking water and health. Although contaminated drinking water can lead to waterborne diseases, these illnesses are often under-reported and the route of exposure cannot always be determined.

Top of Page