Slow sand filter Space Rate filtration Rapid sand filter Occupies large area Small area 0.1-0.4 m3/m2/ hour 5-15 m3 / m2/ hour Effective size of sand 0.2-0.3 mm 0.4-0.7 mm Preliminary treatment Plain sedimentation Chemical coagulation & sedimentation Washing By scraping the sand bed Backwashing Operation Less skilled Highly skilled Loss of head allowed 4 feet 6-8 feet Removal of turbidity Good Good Removal of colour fair Good Removal of bacteria 99.9-99.99 % 98-99%