In this article a large complex of researches on hydrodynamics and heat transfer is carried out on a current of thin film in up flow, down flow and horizontal-tube falling film desalination plants. Based on the results of observation of the mode of movement of a film on such heating surfaces and steam formation, explanations of physical features of hydrodynamics are given, and beat transfer for seawater and their essential difference in relation to distillate is shown. By results of data processing the currents, ensuring stability, minimal charge of seawater are offered for these processes, as well as an equation for calculation of average and maximal thickness of a film. The equations of heat transfer characteristics for all these thin film regimes are obtained.