Abstract: A filter device for a water filter includes a coupling device and a filter cartridge. A water inlet opening and a water outlet opening are formed on the coupling device. The coupling device has an inner casing with a reversed cone shaped through hole in the center. A valve member controlled by an elastic element is configured within the coupling device. The valve member, which includes a hollow rod with through holes formed on the side wall, completely blocks the cone shaped through hole if no filter cartridge is connected. When the filter cartridge is securely fastened to the coupling device, the elastic element is compressed so as to form a water inlet path from the water inlet opening through the coupling device, the valve member and the filter cartridge. A separate water outlet path from the filter cartridge through the coupling device to the water outlet opening provides filtered water ready for drinking.