In motor vehicles many different ways of water entering the fuel supply system can be found. Due to permanent fuel-agitation in diesel-run-motor vehicles the water is carried along with the fuel-stream. Consequently an emulsion is generated with diesel as continuous phase that represents an water-in-oil-emulsion. To protect vehicle-components which are exposed to diesel or rather to the water-in-diesel-emulsion from damage, possible procedural methods for emulsion-destabilisation should be investigated within this work. To clarify whether destabilisation due to this considered methods is possible or not, experiments are done. Series of tests operated with electro-coalescence provide evidence of the practicability of the de-emulsification of water-in-diesel-emulsions in an electrical field. Treatments with ultrasonic do not succeed in reducing the fraction of the disperse phase and lead to further dispersion of the water-in-diesel-emulsion.