A filter cartridge for filtering water, for use in an air humidifier, having a storage chamber for storing filter material, and having at least one opening for feeding to the storage chamber and/or for releasing from the storage chamber the water to be filtered is proposed. For the purpose of relatively quick filling, the filter cartridge is formed to be arranged in a container, containing water to be filtered, such that the filter cartridge can project at least partially into the water stored in the container, with the at least one opening formed both as a water inlet for feeding water from the container into the storage chamber and as a water outlet for discharging water from the storage chamber into the container. A roller, an air humidifier and a filtering method are also proposed.