Abstract: An arrangement (2) for cleansing polluted water that enters into a catch basin includes a container (4), which is intended to be arranged in the catch basin and which has an upper, substantially horizontal intake opening (30) for receiving the downward moving polluted water, and a pollution-absorbing material (6) that is arranged in the container for cleansing polluted water that flows from the intake opening. The arrangement further includes a particle separator (8) which in arranged above the container (4) and which forms an outer surface (18) with a shape such that solid particles in the incoming, polluted water are diverted by the outer surface so that the particles fall outside of the intake opening (30) of the container, whereas water is led in under the particle separator (8) by surface wetting to the outer surface and falls down into the container via its intake opening.