Gravity sand filters (GSF) provide rapid and efficient removal of relatively large suspended particles.

The major parts of a gravity sand filter are:
* Filter Chamber
* Filter media
* Gravel support
* Under drain system

The filter chamber is usually made out of reinforced concrete, filled with sand and gravel

The water is supplied to the top of the sand-bed and filtered as it flows through the layers of graded sand and gravel. A system of perforated pipes on the bottom drains the chamber.

In the course of filtration processes, more and more particles get accumulated and clogs the filter media. The system can be replenished by cleaning the filter bed. This is usually done by backwashing i.e the flow of water is reversed, so that treated water flows backwards through the filter. The sand is re-suspended and the solid matter is separated in the surface water. Air is injected additionally in order to support the cleaning process. Once the backwash is completed the filter is put back to regular operation.