The sand filters perform the filtration through a thick layer of graded particles recognised as depth filtration, These particles can be sand , gravel or granular materials.The filtration rate depends on the effective size of the bedding and velocity through the filter, water enters through the filter inlet and percolates through the filter bed. When the suspended matter comes in contact with sand particles, it absorbs on it. Clean water goes via the filter outlet. Cleaning is done by backwashing, water is inserted in reverse direction from the nozzles upward causing suspension of the filter bed, thus releasing the suspended matter from the bedding and is flushed out through the backwash valve.