A washable filter for purifying water includes an upwardly open, upright vessel. A raw water inlet is provided above a filtration zone in the vessel. A sedimentation chamber is arranged underneath the filtration zone. A vertical wall arranged above the sedimentation chamber divides the filtration zone into two filter chambers, such that the filter chambers are connected to each other only through the sedimentation chamber. One of the filter chambers is arranged below the inlet and an outlet for the filtered water is arranged above the other of the filter chambers. A heavy material pump connected to a sludge outlet pipe is arranged in the sedimentation chamber.