Reverse Osmosis

To understand the process and purpose of Reverse Osmosis, we need to understand the process of Osmosis.

Osmosis is one of the most important processes in nature and a naturally occurring phenomenon. It is the movement of water molecules from higher water concentration to the area of lower water concentration through a semipermeable membrane. In other words, it can be defined as the diffusion of water molecules through a semipermeable membrane. It is a special case of diffusion of water (High to low). For example, water in the roots are transported through osmosis, plant roots absorbing water from the soil, and our kidneys absorbing water from the blood.

For example, water in the roots is transported through osmosis, plant roots absorbing water from the soil, and kidneys absorbing water from the blood.


A less concentrated solution has a natural tendency to migrate to a higher concentration solution. For instance, consider two containers. One container is filled with low salt concentrated solution and another container with a high salt concentration. A semi-permeable membrane separates these two containers, and the water that has a lower concentration would start to migrate towards the water container with a higher salt concentration. A semipermeable membrane is a membrane that allows some molecules to pass but not others.

What is Reverse Osmosis?

A reverse osmosis is a process in which pressure is applied to overcome colligative property and osmotic pressure that is directed by thermodynamic parameter and a chemical difference of a solvent. This application is mainly applied in the production of potable water, in water plants and in industries. The end result will be the solute. It happens when the pure solvent is allowed to follow to one end of the membrane thus allowing a solute to retain in a permissible side of a membrane. Reverse osmosis removes suspended and types of dissolved species from water including bacteria.

Reverse Osmosis

Working Of Reverse Osmosis Plant

Diffusion is a process by which the molecules move from the region of higher concentration to lower concentration. There is a net movement meaning more molecules moving in one direction than in the opposite direction.

In osmosis, the water molecules and the concentration gradient occurs over the semipermeable membrane which allows the entry of water and blocks the passage of ions and other larger molecules including sodium, chlorine, bacteria, glucose, etc.

Reverse osmosis is the process or the technology which is used to remove ions, mineral chemicals, and other impurities from drinking water. In this process, a greater pressure is applied, forcing the water to travel through the semipermeable membrane in opposite to natural osmosis.

Reverse Osmosis works on the same principle as osmosis, but in the reverse direction.In this process direction of water flow is reversed by applying greater pressure.

For instance, consider a semipermeable membrane placed in between the fresh water and concentrated aqueous solution. In natural osmosis, the fresh water will cross the semipermeable membrane and dilutes the concentrated solution. In reverse osmosis, the pressure is applied towards the concentrated aqueous solution and the water molecules are forced to cross the membrane towards the fresh water.

Stay tuned with BYJU’S to learn more about Osmosis, Diffusion and Reverse Osmosis.

Practise This Question

The osmotic pressure at 17°C of an aqueous solution containing 1.75 g sucrose per 150 ml solution is