A system is provided for detecting non-metallic, non-aqueous substances in an aqueous sample, comprising a transmitter section, which emits electromagnetic radiation in the terahertz range towards the sample, a receiver section, which detects radiation components of said electromagnetic radiation which are modified by the sample and/or the substances therein and an evaluation section, which evaluates radiation components which are detected by the receiver section in order to establish whether non-metallic, non-aqueous substances are present or not in the aqueous sample, a transition of the aqueous sample from the liquid aggregate state into the solid aggregate state or vice versa taking place, radiation components which are modified respectively, for a plurality of different states of the aqueous sample, during this transition being detected by means of the receiver section, and the radiation components thus detected being evaluated by means of the evaluation section.