Within the framework of SIR epidemic model with time-dependent recovery rate the time-behavior of infectives for cholera (+ve) and non-choleric diarrhoea has been studied. Here, the population of greater Calcutta has been considered. The infectivity curves for these diseases, as computed from this model, have been fitted with the data available upto 1991 and have been extrapolated upto 2000 years. The steady number of infectives for the forth coming year is being predicted here.