Reverse Osmosis – Definition and Use

reverse-osmosis-systemsWhat is diffusion?

When it comes to osmosis, first we need to understand what diffusion is? This phenomenon occurs all the time. For example, if you pour a spoonful of vinegar into a glass of transparent water, you will have a glass of a mixture of water and vinegar. They mix together. We call a phenomenon similar to this case as diffusion. Generally, diffusion is a phenomenon in which atoms or molecules will move from one region of higher concentration to another region of lower concentration. In this case, a spoonful of vinegar is a region of higher concentration of vinegar and water is a region of lower concentration of vinegar.

What is osmosis?

Well, what is osmosis? Actually, osmosis is a special case of diffusion. In osmosis, the molecules are water molecules that will pass through a membrane that only let water molecules pass through, while other ions and large molecules are not allowed. Naturally, water molecules move from higher concentration side to lower concentration side.

Naturally, both osmosis and diffusion will never stop unless the concentration becomes evenly. They are thermodynamically favorable. As a special case of discussion, when enough pressure is applied to water on one side of the membrane, osmosis can be reversed, stopped, slowed or fastened. When the side of the water where pressure is applied is of high concentration of water, the water molecules will be forced into the lower concentration side, while other large molecules are left on the other side.

What is reverse osmosis?

Generally, reverse osmosis will not happen naturally unless pressure is applied to stop the osmosis. When pressure is applied to the higher concentration side, the water flow will be reversed, moving from higher concentration region to the lower concentration region. This process is very great, because we can use it to filter water. We use the membrane to filter contaminated water. At the first, some water will pass through the membrane to the other side of the membrane. However, when reaching the equilibrium, it will not occur any more. In this situation, the applied pressure on the contaminated water will force the water continuous pass through the semi-membrane, while other contaminants are still left in the higher concentration side. The reverse process separates water from contaminants.

Reverse osmosis is widely used in both commercial and residential water filtration. And there are plenty of reverse osmosis systems that you can install in your house to get clean water to consume. Plus, reverse osmosis is also used to desalinate water, which can relieve the strain on water resources in the future.

Pros & Cons


  • More effective to remove pollutants in the water and more efficient to treat water
  • More economical – Even if the initial cost is high, in the long run, it is more economical than other types of filtration, like carbon filtration, distillation


  • None – May be a little expensive.

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