Sand filtration is a simple process in which the water is allowed to filter through a layer of sand in a specially constructed tank. In the filtration process, the small remaining floc particles are removed by the sand grains and are retained in the bed of sand, while clean water flows out at the bottom of the sand bed. Filters act as sieves and form the final barrier for any particles, whether organic or inorganic. At Midvaal, silica sand is used as filtration medium and the filters are of the rapid gravity type. Two blocks of filters are available at Midvaal.