In the last years the demand for fresh water is increasing tremendously all over the world. The future demand will be very high and the fresh water resources are getting depleted at a faster rate. We need to depend on the brackish water and oceanic water resources for meeting the fresh water demand. Furthermore non-conventional energy resources are required for meeting energy demand. One best option is to use solar energy for water distillation. This paper is about the numerical analysis and modelling of a solar still and enhancing its efficiency by mixing the still water with granular activated carbon. Matlab software is used to simulate the model. Matlab code was written for calculating the various heat fluxes in the still, to determine the hourly output of still and to find the efficiency of the still. Complete numerical analysis and various characteristics graphs of still were plotted using matlab. Simulink tool box is used to simulate the model.