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We Know: Facts on Drinking Water
Where does drinking water come from?
Water for large cities comes form surface water sources, such as lakes, rivers, and reservoirs. The source may be local or from many miles away. It comes from the part of the river or lake that you can see, as well as the entire watershed. In rural areas, people are more likely to drink ground water that was pumped from a well.
How is drinking water treated?
Drinking water may be treated in several ways:
- Water from a river or reservoir often contains dirt and tiny pieces of leaves and other organic matter, as well as trace amounts of certain contaminants. At the treatment plant, water suppliers add chemicals called coagulants to the water. They cause dirt and other contaminants form clumps that settle to the bottom. The water then flows through a filter for removal of the smallest contaminants and viruses.
- Ground water is filtered as it passes through layers of the earth into underground reservoirs known as aquifers. Water that suppliers pump from wells generally contains less organic material than surface water and may not need to go through any treatments.
- The most common drinking water treatment, considered by many to be one of the most important scientific advances of the 20th century, is disinfection. Most water suppliers add chlorine or another disinfectant to kill bacteria and other germs.
- Water suppliers use other treatments as needed. For example, water that is contaminated with organic chemicals can be treated with activated carbon, which adsorbs or attracts the chemicals dissolved in the water.
Where do drinking water contaminants come from?
Contaminants may come from sources. These include:
- Erosion of natural rock formations
- Substances discharged from factories
- Substances applied to farmlands
- Substances used by consumers in their homes and yards
What contaminants can be found in drinking water?
Some of the contaminants found in drinking water are:
- Microbials like pesticides and bacteria
- Disinfection Byproducts
- Radon
- Radionuclides
- Arsenic
What affects does contaminated water have on people?
Health affects caused by water contaminates can be either acute, or chronic.
- Acute effects occur quickly after introduction of bacteria or other contaminant into the water. Most people's bodies can fight off these microbial contaminants the way they fight off germs, and these acute contaminants typically do not have permanent effects. They can be dangerous or deadly for a person whose immune system is already weak due to HIV/AIDS, chemotherapy, steroid use, or another reason.
- Chronic effects occur after people consume a contaminant at levels over EPA's safety standards for many years. Examples of the chronic effects of drinking water contaminants are cancer, liver or kidney problems, or reproductive difficulties.
What is being done to prevent contamination?
Some of the steps taken to prevent drinking water contamination are:
- Drinking water standards have been set by the Environmental Protection Agency.
- Some ground water systems have established wellhead protection programs
- Some surface water systems protect the watershed around their reservoir to prevent contamination.
- States and water suppliers are working systematically to assess every source of drinking water and to identify potential sources of contaminants.
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