During the annual examination of drinking water, an abnormal quantity of cyanide was detected in the distribution network supplying four villages (35,000 people). The polluted water table was used by seven water catchments. One of them was closed following the detection of 250 µg/l (max. authorised concentration – 50 µg/l) of cyanide. The source of this pollution was unknown (industrial site, uncontrolled dumping, etc.). If the situation worsened, it was planned to interconnect the water supply network of the village to the network of adjoining villages. The water table and supplied water were analysed on a daily basis. A legal enquiry was conducted.