Within the scope of a village hydraulic programme, in a Sahel rural area, an investigation was conducted in a school to determine the effect of the use of drinking water on fecal flora. One year following the installation of a hydraulic pump, it was observed that pathogenic salmonellae, shigellae and amoebic cysts had virtually disappeared. In contrast, the perennial character of viral contamination was demonstrated. Water guaranteed potable, therefore, appears to be an essential factor in the prevention of infections due to fecal pathogenic microorganisms. It is essential, however, that the areas surrounding the pumps be subjected to strict supervision to avoid pollution of the underground water sheet.