Coagulation is usually the first step in water treatment. Positively charged chemicals are added to the water during coagulation. The positive charge neutralizes the negative charge of dirt and other dissolved particles in the water. When this occurs, the particles combine with the chemicals to form slightly larger particles. Common chemicals used in this step include certain types of salts, aluminum, or iron.
Flocking follows the coagulation step. Flocculation is the gentle mixing of water to form larger, heavier particles called flocs. Water treatment plants often add additional chemicals during this step to help floc formation.
Sedimentation is one of the steps used by water treatment plants to remove solids from the to separate water. . During sedimentation, flakes settle to the bottom of the water because they are heavier than water.
Once the flakes have settled to the bottom of the water, the clear water above is filtered to separate additional solids from the water. During filtration, clean water goes through filters with different pore sizes and made of different materials (e.g. sand, gravel and charcoal). These filters remove dissolved particles and germs such as dust, chemicals, parasites, bacteria and viruses. Activated carbon filters also eliminate bad smells.