Filtration : The water enters the filter tank through the inlet pipe and is evenly distribute over the top of the sand through a distribution system. As the water flows downward through the sand media, suspend solids, debris, and other impurities are trappe within the sand bed.
Accumulation of contaminants: Over time, the suspend solids and impurities build up in the sand bed, forming a layer known as the filter cake. 
Backwashing: As the filter bed becomes clogged with accumulate impurities, the pressure drop across the filter increases, and the flow rate decreases. To maintain the filter’s effectiveness, a backwashing process is initiated.
Rinse and Return to Service: After backwashing, a rinse cycle follows, during which clean water is pass through the filter to settle the sand and remove any remaining debris.