Water is pumped into the treatment plant from the reservoir or stream through  rotating screens .
Alum is added to cause flocculation .
After rapid mixing (20-40 minutes), the water remains in  the settling basin while sedimentation of floc occurs (2-4 hours). The sediment (sludge) is pumped from the bottom of the pools and stored in holding lagoons to dry.
The softening process  involves the addition of sodium carbonate 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 to lower the pH level to approximately 7.8. Water is held in a  stabilizing basin for another 2-4 hours.
Water then flows through large dual media rapid sand filters made up of layers of gravel, sand, and anthracite coal .
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, neither screening nor initial sedimentation is needed.