Drinking water supplies in the United States are among the safest in the world. However, even in the U.S., drinking water sources can become contaminated, causing sickness and disease from waterborne germs, such as Cryptosporidium, E. coli, Hepatitis A, Giardia intestinalis, and other pathogens.
Drinking water sources are subject to contamination and require appropriate treatment to remove disease-causing agents. Public drinking water systems use various methods of water treatment to provide safe drinking water for their communities. Today, the most common steps in water treatment used by community water systems (mainly surface water treatment) include:
Coagulation and Flocculation Coagulation and flocculation are often the first steps in water treatment. Chemicals with a positive charge are added to the water. The positive charge of these chemicals neutralizes the negative charge of dirt and other dissolved particles in the water. When this occurs, the particles bind with the chemicals and form larger particles, called floc.
Sedimentation During sedimentation, floc settles to the bottom of the water supply, due to its weight. This settling process is called sedimentation.
Filtration Once the floc has settled to the bottom of the water supply, the clear water on top will pass through filters of varying compositions (sand, gravel, and charcoal) and pore sizes, in order to remove dissolved particles, such as dust, parasites, bacteria, viruses, and chemicals.
Disinfection After the water has been filtered, a disinfectant (for example, chlorine, chloramine) may be added in order to kill any remaining parasites, bacteria, and viruses, and to protect the water from germs when it is piped to homes and businesses. Learn more about water disinfection with chloramine and chlorine on the Disinfection page. http://www.cdc.gov/healthywater/drinking/public/water_disinfection.html
Water may be treated differently in different communities depending on the quality of the water that enters the treatment plant. Typically, surface water requires more treatment and filtration than ground water because lakes, rivers, and streams contain more sediment and pollutants and are more likely to be contaminated than ground water.
Some water supplies may also contain disinfections by-products, inorganic chemicals, organic chemicals, and radionuclides. Specialized methods for controlling formation or removing them can also be part of water treatment. To learn more about the different treatments for drinking water, see the National Drinking Water Clearinghouse's Fact Sheet Series on Drinking Water Treatments http://www.nesc.wvu.edu/techbrief.cfm
To learn more about the steps that are taken to make our water safe to drink, visit the United States Environmental Protection Agency's (EPA) Public Drinking Water Systems webpage. http://www.epa.gov/safewater/pws/index.html
Community water fluoridation prevents tooth decay safely and effectively. Water fluoridation has been named one of 10 great public health achievements of the 20th century. For more information on the fluoridation process and to find details on your water system's fluoridation, visit CDC's Community Water Fluoridation page. http://www.cdc.gov/fluoridation/
Consumer Confidence Reports
Every community water supplier must provide an annual report, sometimes called a Consumer Confidence Report, or "CCR," to its customers. The report provides information on your local drinking water quality, including the water's source, contaminants found in the water, and how consumers can get involved in protecting drinking water.