The seasonal distribution of two vibrio species, V. cholarae and V. mimicus, in municipal water of three cities (Khairpur, sukkur and Rohri of Sindh, Pakistan, was investigated using membrane filtration technique. A total of 216 samples were collected over the period of 2005-2007. Samples from the main water storage reservoirs at Khairpur (n=72), Sukkur, (n=72), and Rohri (n=72) were collected at 15 day intervals. Densities of the two vibrio species were determined over this time. Both species were detected in the water of the three cities. Highest prevalence of the two vibrios was noted at Rohri city. Their prevalence turned out to be highly temperature and season dependent. The results show poor quality of the municipal drinking water at all sites, particularly at Rohri. The presence of Vibrio spp. in drinking water of these areas is bound to result in transmission of diarrheal diseases such as cholera.