A system of components which, when assembled, form a rainwater separator for a downpipe, the system consisting of following components: a cylindrical screen, a cylindrical housing tube, a ring-shaped lid having a drain insert for the rainwater, a ring-shaped collecting basin, which has an inside wall and an outside wall and forms a central water outlet, wherein the dimensions of the screen, of the housing tube, of the ring-shaped lid and of the collecting basin are selected such that, in a first assembly arrangement, they can be arranged so that the screen is arranged in the housing tube concentrically with the longitudinal axis of the housing tube, so that an annular space is formed between the screen and the housing tube, the annular space is sealed by the ring-shaped collecting basin on its bottom side, wherein the screen sits on the edge of the inside wall, the cylindrical drain insert for the rainwater is arranged relative to the longitudinal axis of the screen and its lower edge is inserted into the upper end face of the screen, and wherein the outside wall of the collecting basin and the upper edge of the housing tube have the same contour, so that the ring-shaped lid can be placed on the housing tube as well as on the collecting basin to form a tight seal, wherein the dimensions of the ring-shaped lid and of the collecting basin are also selected such that they can be arranged in a second assembly arrangement, such that the ring-shaped lid is placed directly on the outside wall of the collecting basin, omitting the screen and omitting the housing tube, wherein the lower edge of the cylindrical drain insert is situated on the outside radially of the inside wall of the collecting basin, so that rainwater can enter the collecting basin directly, characterized in that a ring-shaped coarse screen is part of the system, its dimensions being selected such that, in the second assembly arrangement, it is arranged between the lower edge of the cylindrical drain insert and the inside wall of the collecting basin. a cylindrical screen, a cylindrical housing tube, a ring-shaped lid having a drain insert for the rainwater, a ring-shaped collecting basin, which has an inside wall and an outside wall and forms a central water outlet, the screen is arranged in the housing tube concentrically with the longitudinal axis of the housing tube, so that an annular space is formed between the screen and the housing tube, the annular space is sealed by the ring-shaped collecting basin on its bottom side, wherein the screen sits on the edge of the inside wall, the cylindrical drain insert for the rainwater is arranged relative to the longitudinal axis of the screen and its lower edge is inserted into the upper end face of the screen, and wherein the outside wall of the collecting basin and the upper edge of the housing tube have the same contour, so that the ring-shaped lid can be placed on the housing tube as well as on the collecting basin to form a tight seal, wherein the dimensions of the ring-shaped lid and of the collecting basin are also selected such that they can be arranged in a second assembly arrangement, such that the ring-shaped lid is placed directly on the outside wall of the collecting basin, omitting the screen and omitting the housing tube, wherein the lower edge of the cylindrical drain insert is situated on the outside radially of the inside wall of the collecting basin, so that rainwater can enter the collecting basin directly,