Automated system for the real time monitoring of total toxicity in water, based on the toxic effects that contaminants have on the microbial metabolism of a continuous biological reference system. This apparatus may be incorporated into a Biological Early Warning System. Before an alarm signal is activated, the device captures a sample of the problem mixture from which posterior analyses can determine the qualitative nature of the toxicity. The capture and conservation of this´problem sample is acheived without interrupting the measurement cycle of the device and continued protection of thewater system.