The Barometric Evaporator is a thermal desalination distillation technology. It uses moderate temperature heat to directly desalinate brackish water or seawater by distillation. The system is easy to operate, easy to maintain with very low electrical power requirements. The systems patented technology lowers water’s boiling point to 122 from 212 degrees. If coupled with heat from renewable energy processes, the system operational costs are well below competing technologies. Saline water is evaporated using ultrasonic cavitation. This is a highly energy efficient process to produce heat and bubbles within an air free tube while flowing upward from a higher to lower pressure. Both the pressure difference and the expanding volume of vapor released by the saline water serve to drive saline water at increasing concentration up a tube against gravity. When the saline water inside the tube is heated by steam condensing on the outside, up to 200% improvement in heat transfer performance has been shown, caused by reducing the water in contact with the tube surface to a thin film. The Barometric Evaporation Process uses heat energy for evaporation introduced into the saline water before it is fed to a flash channel. A two-phase flow occurs. The saline water in the flash channel is allowed to cool as it rises in the flash channel releasing heat energy to evaporation. The process uses heating energy input from a kinetic chemical reaction in the water & power transformer stage. The features include the use of rising and falling barometric legs for feed from concentrate reject to atmospheric pressure respectively, vapor separation in an evacuated chamber at the top of the unit, a condenser at the top of the unit to recover distillate, and the use of low grade waste heat, solar, thermal or sonic cavitation heat to drive the evaporation process. The Barometric Evaporation Process uses a flash inducing orifice and vertical flash channel to facilitate evaporation in the rising saline water feed column and help draw feed upward against gravity. Barometric Evaporator applies a continuously declining pressure on the source water as it rises in a flash channel. The Barometric Evaporation Process is intended to operate efficiently over a range of low to moderate temperatures (120 f to 210 f).