NOVELTY - A fuel cell system comprises fuel cell module; water supply apparatus; water container (16); and condenser. The water container has supply port (22) to supply water from condenser to water container, a discharge port (24), and a water channel (26) as a passage for water from the supply port to the discharge port. The water channel has an ion exchanger section (28) for removing impurities contained in the water supplied from the condenser and reversing sections (30a) for reversing a flow direction of the water.    USE - As fuel cell system (claimed) used as a stationary fuel cell system, a vehicle-mounted fuel cell system, or the like.    ADVANTAGE - The fuel cell system has a simple and compact structure in which a desired water processing function is maintained, improvement in the durability is achieved, and the maintenance cycle is extended. Further, since the ion exchanger section is included in the water container, there is no restriction on material that can be used for the water container, and the material can be selected more freely. The entire area of the ion exchanger section can be utilized effectively, and the ion exchanger section can be used effectively over a long period of time. Thus, durability of the ion exchanger section is improved, and the maintenance cycle of the ion exchanger section is extended easily.    DETAILED DESCRIPTION - A fuel cell system comprises a fuel cell module for generating electrical energy by electrochemical reactions of a fuel gas and an oxygen-containing gas; a water supply apparatus for supplying water to the fuel cell module; a water container (16) for supplying water to the water supply apparatus; and a condenser for condensing water vapor contained in an exhaust gas discharged from the fuel cell module and supplying the condensed water to the water container. The water container has a supply port (22) for supplying the water from the condenser to the water container, a discharge port (24) for sending the water to the water supply apparatus and a water channel (26) as a passage of the water from the supply port to the discharge port; and the water channel has an ion exchanger section (28) for removing impurities contained in the water supplied from the condenser, and reversing sections (30a) for reversing a flow direction of the water.    DESCRIPTION OF DRAWING(S) - The figure shows a cross sectional side view of the water container.    Water container (16)    Supply port (22)    Discharge port (24)    Water channel (26)    Ion exchanger section (28)    reversing sections (30A)