The gravity sand filter or rapid gravity filter are most commonly used in Municipal water purification plants
worldwide. They use relatively coarse sand and other granular media to remove particles and impurities that
have been trapped in a floc through the use of flocculation chemicals. Water and flocs flows through the
filter medium under gravity and the flocculated material is trapped in the sand matrix.
These filters are typically designed as part of multi-stage treatment systems used by large municipalities.