American Water
Works Association

Surface Water entering a water treatment plant contains lots of natural, organic particles suspended in the water. These particles make the water appear cloudy. This is often referred to as turbidity, which is a measurement of how clear the water is. The goal of the water treatment process is to decrease turbidity, making the water clear and removing any particles that may be harmful. The most common type of water treatment, known as conventional water treatment. These are the steps of that process:

Pre-sedimentation, Coagulation/Flocculation, Sedimentation, Disinfection

Watch this part of the video about water treatment.

  • The first step Pre-Sedimentation, is to slow the water down so heavy particles can settle out.
  • Next, chemicals are added to the water and gently mixed to bring the suspended particles together. This is called Coagulation/Flocculation. The small particles collide with each other and stick together forming larger particles.
  • The water continues through the plant to a Sedimentation basin where the large particles settle to the bottom of the basin and are removed from the water.
  • Water flows out of the top of the basin into a filter to remove the remaining particles. Filtration makes the water clear.
  • The final step is Disinfection, where a chemical such as chlorine is added, to remove and prevent potentially harmful microorganisms from growing. A small amount of disinfectant is required to be in the drinking water system and maintained until the water is delivered to homes and businesses.