Commonly used in desalination, Multi-Stage Flash Distillation involves the heating of seawater in a container known as a brine heater. This is usually achieved by condensing steam on a bank of tubes carrying seawater through the brine heater. Thus heated, the water is passed to another container known as a "stage", where the surrounding pressure is lower than that in the brine heater.

It is the sudden introduction of this water into a lower pressure "stage" that causes it to boil so rapidly as to flash into steam. As a rule, only a small percentage of this water is converted into steam. Consequently, it is normally the case that the remaining water will be sent through a series of additional stages, each possessing a lower ambient pressure than the previous "stage".

As vapor steam is generated, it is condensed on tubes of heat exchangers that run through each stage.

water - multi stage flash distillation