Device for treating water of a water body, having a first arrangement by means of which the water of the water body can be conveyed upwards through a pipe (17, 63) which extends in approximately vertical direction, a second arrangement being present, which is connected to the first arrangement and contains a calcareous granulate, past which the water can flow, so that the water can absorb lime particles, characterized in that the second arrangement is connected to the first arrangement and contains a calcareous granulate, which the water can flow past, so that the water can absorb lime particles, and in that the second arrangement contains a calcareous granulate, which the water can flow past, so that the water can absorb lime particles, characterized in that the second arrangement contains a calcareous granulate, which the water can flow past, so that the water can absorb lime particles, characterized - in that an upper end of the pipe (17, 63) is located below the water surface; - in that the first assembly has a platform carried by floats, - in that the pipe (17, 63) is arranged on an underside of the platform, - in that an electric motor is mounted on the platform, which drives a paddle wheel inside the pipe (17, 63) via a shaft, the shaft extending approximately coaxially with the pipe (17, 63) and extending from the electric motor into the upper region of the pipe (17, 63) below the upper end of the pipe (17, 63), and the paddle wheel being fastened to a free end of the shaft; - in that the second arrangement has a conveying device with which the water can be conveyed from the pipe (17, 63) in the direction of an outlet and can be discharged into the water body in the region of the water surface, - in that the second arrangement is arranged in the region of the water surface of the water body, - in that the second arrangement has a trough in which the granulate is contained, which is connected to the pipe (17, 63) and through which the water can be passed, and in that the second arrangement has a tank in which the granulate is contained, which is connected to the pipe (17, 63) and through which the water can be passed, and in that the second arrangement has a tank in which the granulate is contained. - in that the trough has a perforated plate on the upper side of which the granules are deposited. - in that an upper end of the pipe (17, 63) is located below the water surface; - in that the first assembly has a platform carried by floats, - in that the pipe (17, 63) is arranged on an underside of the platform, - in that an electric motor is mounted on the platform, which drives a paddle wheel inside the pipe (17, 63) via a shaft, the shaft extending approximately coaxially with the pipe (17, 63) and extending from the electric motor into the upper region of the pipe (17, 63) below the upper end of the pipe (17, 63), and the paddle wheel being fastened to a free end of the shaft; - in that the second arrangement has a conveying device with which the water can be conveyed from the pipe (17, 63) in the direction of an outlet and can be discharged into the water body in the region of the water surface, - in that the second arrangement is arranged in the region of the water surface of the water body, - in that the second arrangement has a trough in which the granulate is contained, which is connected to the pipe (17, 63) and through which the water can be passed, and in that the second arrangement has a tank in which the granulate is contained, which is connected to the pipe (17, 63) and through which the water can be passed, and in that the second arrangement has a tank in which the granulate is contained. - in that the trough has a perforated plate on the upper side of which the granules are deposited.