 The increasing global demand for freshwater has driven the development and implementation of various seawater desalination technologies. To assess the efficiency of these technologies, entropy generation analysis can be used to illustrate the influence of irreversibility on the required energy input. This analysis focuses on the minimum amount of useful exergy, the minimum amount of work needed to separate a unit of water from a given salinity required to extract a unit of water from a feed stream. The second law efficiency is then calculated as the ratio between the useful exergy output and the total exergy input. By applying physical models, the magnitude of entropy generation by different components and processes can be estimated. This includes entropy generated during the rundown to equilibrium of discharge streams, which must also be taken into account when calculating the total entropy generation. The relative importance of each source of entropy generation can then be determined, allowing for the identification of which systems operate closest to the reversible limit and which have the greatest potential for improvement.