Compared to conventional thermal desalination, only 15 % of energy is required to desalinate seawater. Freeze Desalination (FD) is a freezing-melting process in which freshwater in the form of ice crystals is separated from a seawater solution and eventually melted. Since ice crystals are made of only pure water, they reject salt in the rest of the solution making the solution further concentrated. Additionally, using unidirectional freezing, cornering out of impurities or salt is possible, thus making it easy to separate formed ice. In this work, an aqueous solution of NaCl and pure water is allowed to freeze from top (like mother nature does to lakes) in a rectangular cavity. Then it is experimentally and numerically assessed. A 2D planar CFD model of the freeze desalination process using species transport during solidification/melting and energy equation is developed to simulate the experimental apparatus. Numerical results show a successful top freezing where salt diffuses away from the freezing front and is carried away by the convection created by the thermo-solutal gradient. Its behaviour is analysed, when the freezing front progress. Experimental findings reveal four distinct regimes observed in the temperature history of the bottom surface, indicating the behaviour of thermo-solutal convection during the progression of the freezing front. The impact of input salinity on this signature is being examined.