NOVELTY - An apparatus (70) for supplying water to a reformer in a fuel cell system, comprises a constant-volume container (71) receiving water and fuel; and a separation layer (78) located between and in contact with the fuel and water in the container, to transmit pressure of the fuel to the water. The fuel is positioned above the water. The separation layer is formed of a material that floats on the water in the container.    USE - As an apparatus for supplying water to a reformer in a fuel cell system; useful in a fuel cell system (claimed) such as polymer electrolyte membrane fuel cell system, used in electronic devices and transportation vehicles.    ADVANTAGE - The water supply apparatus provides controlled supply of water to the reformer in the fuel cell system. The separation layer transmits pressure of fuel to the water in the water supply apparatus. Thus, the water supply apparatus discharges water using the pressure of fuel (e.g. gaseous fuel), eliminating the use of a pump for supplying water to the reformer in fuel cell system. As a result, the water supply apparatus provides a compact and lightweight fuel cell system, with reduced noises and electric consumption. In addition, the separation layer blocks contact of the gaseous fuel with water. Therefore, bubble generation due to the fuel is restrained. As a result, it is possible to supply water to the reformer in corresponding quantity, so that efficiency of the fuel cell system is increased.    DETAILED DESCRIPTION - An apparatus (70) for supplying water to a reformer in a fuel cell system, comprises a constant-volume container (71) receiving water and fuel; and a separation layer (78) located between and in contact with the fuel and water in the container, to transmit pressure of the fuel to the water. The fuel is positioned above the water. The separation layer is formed of a material that floats on water in the container. The separation layer is preferably a liquid layer containing a liquid material (e.g. oil) that is immiscible with the fuel and water. The separation layer is preferably a flexible film. The container is connected to a fuel tank and a reformer of the fuel cell system. The container has a water opening for water input/output, and a fuel opening for fuel input/output. An INDEPENDENT CLAIM is included for controlling a supply of water to a reformer in a fuel cell system, involving providing the container containing water and fuel, separated by the separation layer; and flowing fuel into the container such that the fuel is pushed against the water via the separation layer, to cause the water to flow out of the container to the reformer.    DESCRIPTION OF DRAWING(S) - The figure shows a sectional view of a water supply apparatus useful in a fuel cell system.    Water supply apparatus (70)    Container (71)    Water-accommodating portion (73)    Fuel-accommodating portion (75)    Separation layer (78)    Oil layer (79)    Fuel tank connecting line (81)    Reformer connecting line. (83)