The invention includes a device for determining the moisture or conductivity of a medium in a container. A measurement probe is plunged into the medium and consists of a conductive material, a conductive rod, and a first feed-through component designed such that the conductive rod can be fastened to an electrically conductive wall or holder. A rod of a non-conductive material and a second feed-through component are provided, where the non-conductive rod can be fastened to the wall, the conductive rod and the non-conductive rod are dimensioned and oriented that the measurement probe is oriented parallel to the longitudinal axis of the container and a signal-processing unit designed such that high-frequency measurement signals are conducted via the measurement line to the measurement probe and that the moisture or the conductivity of the medium is determined by means of a TDR method.