We can explain the term “reverse osmosis” as follows:

To desalinate water, we must create a flow through a membrane, causing the water to leave the salty side of the membrane, flowing into the unsalted side. To achieve this, pressure must be created upon the water column on the salt side of the membrane; firstly, to remove the natural osmotic pressure and secondly, to create extra pressure on the water column, in order to push the water through the membrane. For the desalination of seawater, the pressure must be about 50-60 bars.

There are several different techniques that can be applied for water desalination. Examples are reverse osmosis, electro dialysis, distillation and ion exchange.
Reverse osmosis is the most economic process for the desalination of brackish water and seawater. When we compare this process to the traditional thermic process of distillation, the capital investments and the energy use are much lower.