a fuel cell system includes a fuel cell 1 , a fuel supply 2 , and a oxidant supply and / or oxygen supply 3 . fuel 4 is supplied to an anode 6 of fuel cell 1 and oxygen 5 is supplied to a cathode 7 of fuel cell 1 . fuel cell 1 also has a membrane 8 . in the variant shown as an example , fuel supply 2 has a gas tank 10 , a pressure reducer 11 , a pressure regulating valve 12 and pressure sensors 9 . oxygen supply 3 also has a compressor 13 , e . g ., a fan or a supercharger , and a pressure sensor 14 . a conditioning unit according to the present invention is located downstream of cathode 7 . the conditioning unit includes a pressure regulating valve 16 and exhaust - gas after - treatment 17 , and an optional sensor 18 for measuring the temperature and / or humidity of the cathode outflow . a control unit , which is not shown , evaluates the values determined by sensor 18 and monitors exhaust - gas after - treatment 17 . the exhaust - gas after - treatment heats , e . g ., the cathode flow in such a manner that , when the cathode flow enters the surroundings , it does not condense or form steam . the control unit includes an optional temperature sensor 19 for detecting ambient temperature and / or a humidity sensor 20 for detecting the ambient humidity . with this , e . g ., the operation of conditioning unit 15 can be matched to the ambient parameters . for example , if heating the cathode exhaust gasses to a temperature at which the dew point of the exhaust gas is markedly below the exhaust - gas temperature , the water vapor no longer condenses in the exhaust gasses , in particular since dilution of the exhaust gasses with the ambient air after the exhaust gasses leave the exhaust pipe is sufficiently high . as a result , the dew point constantly remains below the outside temperature . water does not condense out . the temperature can be raised via re - warming using an electric heater 17 or the like ( after - treatment ). likewise , the system temperature of fuel cell 1 can be raised by as much as possible ( e . g ., to approximately 90 - 95 ° c . ), so that the distance from the dew point ( e . g ., approximately 80 ° c .) and exhaust - gas temperature is as great as possible ( pretreatment ). in addition , the dew point of the cathode exhaust gasses can be changed by varying the lambda air value such that the distance increases again ( pretreatment ). since exhaust - gas after - treatment requires a relatively high energy expenditure , the heating can take place mainly at correspondingly low outside temperatures , e . g ., lower than approximately 5 ° c ., and / or at high ambient humidities , e . g ., greater than 80 %, to a minimum extent . to this end , the temperature and , possibly also the humidity of the outside air can be detected using sensors 19 , 20 . in addition , the after - treatment can be limited to start - up phases in which the temperature of the exhaust gasses is relatively close to the dew point . it is also possible for after - treatment to not be carried out at the lowest temperatures , either . it can be intentionally shut off , e . g ., if the driver wants to release steam ( for fun ), or if he wants to drive in an energy - saving mode . it is also possible to realize a coloration of the outflowing exhaust gas or steam , which can increase driving fun in particular or can be used for display purposes . for example , it could be used to signal an impairment and / or failure or the like of a vehicle component , in particular of safety - relevant component and / or the fuel cell system or one of its parts . signaling for these purposes is always an advantage with any type of vehicle . in general , with the aid of the present invention , formation of condensate ( formation of droplets , wetness underneath the vehicle , etc .) can be prevented by dissipating the cathode water in a gaseous state into the surroundings . it is also possible to prevent the formation of ice at cold points in the road where vehicles must often come to a standstill , e . g ., as traffic lights , barriers , etc ., or at points where vehicles typically lose water droplets , e . g ., on uneven surfaces , changes in inclination , etc . generally speaking , the present invention can be used at least with fuel cells 1 for vehicle drives and / or as an “ apu ”. it will be understood that each of the elements described above , or two or more together , may also find a useful application in other types of constructions differing from the types described above . while the invention has been illustrated and described as embodied in a fuel cell system with a hydrous fluid flow , it is not intended to be limited to the details shown , since various modifications and structural changes may be made without departing in any way from the spirit of the present invention . without further analysis , the foregoing will so fully reveal the gist of the present invention that others can , by applying current knowledge , readily adapt it for various applications without omitting features that , from the standpoint of prior art , fairly constitute essential characteristics of the generic or specific aspects of this invention .