Desalination of seawater using reverse osmosis involves the application of pressure to the solution. Reverse osmosis is a process in which pressure is applied to a solution to force water molecules through a semipermeable membrane, leaving behind salts and impurities.

In reverse osmosis, the pressure applied is larger than the osmotic pressure. Osmotic pressure is the pressure required to prevent the flow of solvent (in this case, water) across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration. In the case of seawater, the solute concentration is higher than that of the pure water on the other side of the membrane.

By applying pressure larger than the osmotic pressure, the flow of water molecules is reversed, allowing them to move from the region of higher solute concentration (seawater) to the region of lower solute concentration (pure water). This allows the separation of pure water from the salt and impurities in the seawater.

It is important to note that the pressure applied in reverse osmosis is higher than the osmotic pressure to overcome the natural tendency of water to flow from a region of higher solute concentration to a region of lower solute