Separator arranged in a container of circular or elliptical cross-section and having a container wall for separating a light liquid/water mixture such as for example oil-contaminated water, comprising: an inlet arranged at a first side of the container and having an inlet baffle which guides the supplied mixture downward and divides it into two flow portions (75, 75') of substantially equal size, an outlet having a drain pipe for draining the water, a flow wall of circular or elliptical cross-section and having an inner wall side and an outer wall side, wherein the flow wall passes through at least half of a full circle, preferably at least three quarters of a full circle and exhibits an opening facing a second side of the container opposite the inlet, wherein the flow wall, between the outer wall side of the flow wall and the container wall, forms two flow ducts (70, 71) at two opposite sides of the container wall each from the inlet to the second side of the container, wherein in each case a first one of the two first flow portions (75, 75') is guided within the flow ducts (70, 71) from the inlet to the second side of the container along the container wall such that the two first flow portions (75, 75') will meet at the second side of the container with substantially opposite flow directions and will be reunited, and perforated elements (9 - 12) which are arranged in the two flow ducts (70, 71) and through which the two first flow portions (75, 75') flow. an inlet arranged at a first side of the container and having an inlet baffle which guides the supplied mixture downward and divides it into two flow portions (75, 75') of substantially equal size, an outlet having a drain pipe for draining the water, a flow wall of circular or elliptical cross-section and having an inner wall side and an outer wall side, wherein the flow wall passes through at least half of a full circle, preferably at least three quarters of a full circle and exhibits an opening facing a second side of the container opposite the inlet, wherein the flow wall, between the outer wall side of the flow wall and the container wall, forms two flow ducts (70, 71) at two opposite sides of the container wall each from the inlet to the second side of the container, wherein in each case a first one of the two first flow portions (75, 75') is guided within the flow ducts (70, 71) from the inlet to the second side of the container along the container wall such that the two first flow portions (75, 75') will meet at the second side of the container with substantially opposite flow directions and will be reunited, and wherein the flow wall, between the outer wall side of the flow wall and the container wall, forms two flow ducts (70, 71) at two opposite sides of the container wall each from the inlet to the second side of the container, wherein in each case a first one of the two first flow portions (75, 75') is guided within the flow ducts (70, 71) from the inlet to the second side of the container along the container wall such that the two first flow portions (75, 75') will meet at the second side of the container with substantially opposite flow directions and will be reunited, perforated elements (9 - 12) which are arranged in the two flow ducts (70, 71) and through which the two first flow portions (75, 75') flow.