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. The central concern is waterborne pathogens including but not limited to
, Hepatitis A,
Drinking water sources are subject to contamination from agriculture, discharge of human waste 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 the following:
Coagulation and Flocculation
Coagulation and flocculation are often the first steps in water treatment. Chemicals with a positive charge (Al
) are added to the water. The positive charge of these chemicals neutralizes the net negative charge of dirt, clay and other small dissolved particles in the water that cause turbidity. When this occurs, the particles bind with the chemicals and form larger particles, called floc.
During sedimentation, floc settles to the bottom of the water supply through gravitational settling
Once the floc has settled to the bottom of the water supply, the clear water on top will pass through rapid filters of varying compositions (sand, gravel, and charcoal) and pore sizes, to remove particles, including small flocs, dust, parasites, bacteria, viruses, and chemicals.
After the water has been filtered, a disinfectant (for example, chlorine or chloramine) may be added to kill any remaining parasites, bacteria, and viruses, and to stabilize the water against microbial growth as it is piped to homes and businesses.