Abstract: A process and apparatus for the treatment of untreated water. The untreated water mixed with a flocculating agent is introduced tangentially into the circumferential area of a tank through a feed connection directed at the tank wall. The tank includes a perforated partition circumferentially spaced from the wall of the tank and a conduit in the center of the tank which passes axially through the tank bottom and whose upper end carries a circular overflow disc located below the water level of the tank. Alternately, the partition comprises upper and lower rings, between which there are disposed guide plates which form openings distributed over the circumference of the partition. The circumferential speed of the water flowing through the partition is reduced by braking such that the occurrence of upwardly directed, secondary flows is prevented and clean water is led downward through the center of the tank.