A way to purify water by using a pressure floatation method

PURPOSE: Provided is a method for purifying water in-situ using a dissolved air flotation (DAF) process, thereby treating even sediment deep in the water in situ. CONSTITUTION: The method comprises the steps of supplying pressurized water deep inside water to be treated using a pressurized water distributor(3), and scooping or pumping sediments up to a position from where the pressurized water is distributed using a sediment suction unit(1) and a sediment transporting pipe(2) so that the sediment comes into contact with the pressurized water, and contaminants in the sediment are floated and removed on the surface of water and cleaned materials (sand, gravel) are redistributed onto the bottom of a river.