The single media filtration by use of filter sand is widely spread as a general filtering method. However in these days the treated water quality standards are tightened in addition to the deterioration problem of raw water quality arisen from the growth of algae and cryptosporidium, the part of filtration, which is a key point of water purification become more important and performace is required. Pre-filtration to protect membrane process from fouling. Filtration of cooling water to prevent heat exhanger fouling. Pressure filters uses granular media to remove contaminants from water.