Abstract: A method and a basin serve the purpose of sedimenting sludge in waste water, which in a flow is supplied to the basin via an inlet and in clarified condition is removed via an outlet placed opposite to the inlet. In the inlet there has been built in resistances of flow which create a heavy turbulence in the water flowing and transform a substantial part of the energy of flow from the water into energy in the whirls which create the turbulence. Thereby there are created flow conditions which increase the creation of sludge flocs and the succeeding sedimentation of these.