What is Reverse osmosis (RO) system?

Representative Reuters photo

Reverse osmosis (RO) is a scientific principle based on the pressure of liquids to remove contaminants from unpurified water. It is also a popular method used in water purification machines and plants used for drinking water and other domestic purposes.

Unpurified water from the source is put into a container and pressure is applied to the water. This pressurised water is forced to flow through a semipermeable membrane.

The membrane only allows molecules of a certain size to flow through and to the other side of a membrane which is a catchment area for the purified water. The molecules that are trapped and cannot go through the membrane belong to various impurities such as dissolved salts, minerals, particles, colloids, organics and bacteria from the unpurified water. 

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An RO membrane rejects contaminants based on their size and charge. Most properly working RO systems remove over 99% of these contaminants although they cannot be relied upon to remove 100% of viruses and bacteria. The membrane used the system requires chlorine to be removed from the water beforehand in order to preserve the membrane.

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Though this the central process of a reverse osmosis machine, most domestic RO systems process the water before and after the central RO process. Some of these processes include sediment filtration to remove rust, calcium carbonate and an activated carbon filter before the RO process and sometimes, a secondary carbon filter and UV sterilisation after the process. Although this is how a typical domestic reverse osmosis machine works, there may be some variations based on what the use case of the machine may be and manufacturer of the reverse osmosis plant.

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