Water Treatment Process
The City of Columbus, Division of Water uses a complex multi-barrier approach utilizing state of the art equipment and the latest treatment technologies.
Water flows (1) to the treatment plant from the reservoir or stream through rotating screens (2) to remove large debris.
It is then pumped into the plant where alum is added (3) to cause coagulation.
After rapid mixing, the water remains in the settling basin (4) while sedimentation of floc occurs (2-4 hours). The water treatment residual (settled floc) is pumped from the bottom of the pools and stored in holding lagoons to dry.
The softening process (5) involves the addition of sodium carbonate (soda ash) or caustic soda and hydrated lime to remove calcium and magnesium ions that are responsible for water hardness. This process takes an additional 2-4 hours. For each pound of chemical used in the treatment process, two pounds are removed.
After an additional sedimentation process, carbon dioxide is added (6) to lower the pH level to approximately 7.8.
Ozone is then added to the water to reduce dissolved organic matter (7). Water then flows through large biologically active filters made up of granular activated carbon (8) to remove any remaining particles and further reduce dissolved organic matter.
Addition  of chlorine to disinfect the water, fluoride to protect teeth and a corrosion inhibitor take place at the end of the process before water enters  large underground clearwells to be held until needed by the community .
Please note: When ground water is used (as in the case of the Parsons Avenue Water Plant), neither screening (2) nor initial sedimentation (3,4), nor ozone (7) is needed.