Coagulation and FlocculationCoagulation 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 to the chemicals and form larger particles, called floc.SedimentationDuring sedimentation, floc settles to the bottom of the water supply, due to its weight. This settling process is called sedimentation.FiltrationOnce 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.DisinfectionAfter 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. 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 groundwater because lakes, rivers, and streams contain more sediment and pollutants and are more likely to be contaminated than groundwater.
Some water supplies may also contain disinfection 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.
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. To learn more about the 90+ contaminants EPA regulates and why, visit EPA's Drinking Water Contaminants page.