Many water bodies used for water supply may contain solid particles with a lower density. These solids are hardly removed in the sedimentation unit due to the own tendency of floating. In order to treat this type of water, the dissolved air flotation (DAF) unit is known to be an effective method. A series of laboratory experiments has been performed to investigate the characteristics of solid separation followed by simplification of DAF models in water treatment processes. Results of DAF treatment studies show that total solids removal efficiency depended on the amount of solids attached to bubble on the water surface and residual floating solids in the water. For the enhancement of solid removal efficiency, It is to be desired that surface loading should be operated less than rising velocity of residual floating particles as well as air volume concentration enough.