Multi-stage flash distillation (MSF) is a water desalination process that distills sea water by flashing a portion of the water into steam in multiple stages of what are essentially countercurrent heat exchangers. Current MSF facilities may have as many as 30 stages.

Multi-stage flash distillation plants produce about 26% of all desalinated water in the world, but almost all new desalination plants currently use reverse osmosis due to much lower energy consumption.