This paper evaluates the microbiologic quality of oral rehydration solution (ORS) prepared at a hospital during a cholera epidemic in Guinea-Bissau. The study tested a simple intervention using special vessels for disinfecting tap water with bleach and for preparing, storing, and dispensing ORS. Subjects included approximately 80% of the cholera patients seeking treatment, who were referred to the cholera ward of Simao-Mendes National Hospital. Results suggest that only few coliform bacteria and Escherichia coli were recovered from tap water; however, pre-intervention ORS contained numerous bacteria including E. coli and toxigenic Vibrio cholerae O1. In contrast, ORS samples from intervention vessels had few or no coliform bacteria, no E. coli, and no V. cholerae. This simple system using bleach disinfectant and special storage vessels prevents bacterial contamination of ORS and reduces the risk of nosocomial transmission of cholera and other enteric pathogens.