Basically, after a screen filter has removed larger debris, a media filter such as a rapid sand filter will further filter out organic matter like algae and bacterial sludge as well as fines. sediments such as silt and clay (Bartok, 2009). However, this treatment requires a large surface area. It may be different from the other media filter which is a slow sand filter. (Figure 1.5) As slow sand filtration used much finer sand than the rapid sand filter where the sand used was coarser than 1 mm