These filters are normally used to remove suspended solid substances that cause turbidity from water. Their operation is very simple and consists in allowing water to pass through several layers of quartzite (sand) and, possibly, a layer of anthracite. The water passes through the filtering part, moving in the top-down direction, and during the process the substances retained on the first upper layer of sand increase filtration efficiency in the subsequent layers

To clean the sand and thus regenerate the filter it is necessary to perform a backwash, whereby water (or water and air) passes through the filter from the bottom upwards, so that the backwash water will draw the previously filtered substances towards the point of discharge.