Scientists and engineers are making progress in the technology of seawater-desalination plants. There are three major ways these plants remove salt and other minerals from seawater or brackish water:
Reverse Osmosis: The system takes in ocean or seawater through a water intake system (at a speed three times slower than a fish swims, to protect fish and marine life from getting caught). The water is then pumped through a pipe onto land, where it goes through a filtration system to remove all particles: colloids, algae, and sand. Only saltwater remains. Very high levels of pressure are then applied to push this salty water through a very finely permeable membrane. Incoming water is separated into desalted water and brine. After being treated and diluted, the brine is returned to the sea. The pure water is enriched with mineral salts, such as calcium and carbonates, and pumped into a city’s water distribution system
Multi-Effect Desalination: MED works on the principle of evaporation or distillation, like the natural precipitation cycle, whereby the Sun causes water to evaporate, leaving behind its salt, before falling as fresh rain. In MED, seawater is brought into a chamber and is sprayed over heated pipes, which like the Sun, cause it to evaporate. This hot water vapor, partly cleansed of its salt, cools and condenses into hot liquid water and enters a second, connected chamber. The process is repeated through as many as 14 chambers, in which the water is increasingly desalted into clean water, while recapturing as much of the heat as possible.
Multi-Stage Flash Desalination: MSFD works on the same general distillation principle as MED. The difference is using pressure rather than temperature to evaporate the water. The salty water is heated to between 90° and 110° Celsius (194-212° F) under low pressure, causing the liquid to flash into water vapor. The vapor is passed through successive boilers/chambers, where the process is repeated and even more salt is removed, broadly paralleling the MED process.