NOVELTY - The mobile room with an additional unit (10), comprises a fuel cell system (12) and a sea water desalinating component of a desalination device (14, 16, 18) for the desalination of water to be desalinated. The fuel cell system provides the desalination device occasionally or indirectly with a first energy that is a nonthermal energy form, and with a second energy, whose energy form is different from the energy form of the first energy, and provides the desalination device occasionally or indirectly with electric, thermal-, mechanic, hydraulic, pneumatic and/or chemical energy.    USE - Mobile room such as land vehicle, air craft, floatable device or a mobile or half mobile housing useful for desalination of sea water.    ADVANTAGE - The mobile room requires less space and ensures complete desalination of sea water with low operation and maintenance costs.    DETAILED DESCRIPTION - The mobile room with an additional unit (10), comprises a fuel cell system (12) and a sea water desalinating component of a desalination device (14, 16, 18) for the desalination of water to be desalinated. The fuel cell system provides the desalination device occasionally or indirectly with a first energy that is a nonthermal energy form, and with a second energy, whose energy form is different from the energy form of the first energy, and provides the desalination device occasionally or indirectly with electric, thermal-, mechanic, hydraulic, pneumatic and/or chemical energy. The desalination is based on through-pressing of the water to be desalinated through a membrane (22). The desalination is based upon an evaporation of the water to be desalinated. The desalination device comprises two, three or more desalination steps and a filter for cleaning the water to be desalinated and is arranged for conventional-, cooling-, or drinking water extraction. The additional unit serves an air conditioner. The mobile room comprises a load compensation control that serves a power of the fuel cell system to such periods reinforces to lead to the desalination device in which a total thermal or electric power reduction of the energy consumers (20, 50, 74, 76) is lower than the fuel cell system in an optimal operation area. The mobile room comprises a water jet drive, whose water jet pump occasionally serves to press the water containing in the water to be desalinated through the membrane. The mobile room is a land vehicle, air craft, floatable device or a mobile or half mobile housing. An INDEPENDENT CLAIM is included for a method for desalination of sea water by additional unit for air-conditioning and/or power supply.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of additional units of mobile room.    Additional units (10)    Fuel cell system (12)    Desalination device (14, 16, 18)    Energy consumers (20, 50, 74, 76)    Membrane. (22)