A dust filter includes a filter medium configured to filter foreign substances, such as dust, from atmospheric air. The dust filter also includes a case within which the filter medium is disposed. A first chamber in the case on one side of the filter medium defines a clean side, and a second chamber in the case on the other side of the filter medium defines a dirty side. The case includes a first port that provides fluid communication between the first chamber and the air passage, and a second port that provides fluid communication between the second chamber and the surrounding atmosphere. The second port is configured to allow water accumulated in the case to drain to the outside of the case by gravity while the case is mounted on the vehicle.