Since drinking water still is a problem in case of likely bio-incidents, the necessity to rediscover strategies for the treatment and disinfection of water remains a priority. The aim of our investigation was to establish the potential of using clays as disinfection materials for industrial applications and for household water treatment. In order to determine the efficiency of using clays as disinfecting agents, water samples from different sources were subjected to the action of different quantities of clay using a specific contact time. The antimicrobial effect against faecal indicator bacteria from water (total and faecal coliforms and faecal streptococci) was investigated by using the multi-tube test method as described in STAS 3001/1991-Water/Bacteriological analysis. The results point out the antimicrobial effect of clays and help us understand similar processes in nature - the role of nanoparticulate fraction in self-purification of waters.