How Does Reverse Osmosis Work?

While the term osmosis is well known to junior high school students, reverse osmosis often first becomes known to those individuals who read the side of their bottled water bottles. Reverse osmosis is, quite simply, a method in which water impurities are taken out of a bottle of water thereby making the water safe to drink. However, how does reverse osmosis work as a water purification technology and what impacts the quality of the reverse osmosis process? These concepts will be the focus of this article.

Starting with Osmosis

To understand reverse osmosis it is important to understand osmosis. Osmosis works through the movement from a liquid that contains a high concentration of a substance into that of a lower concentration of a substance in a natural process. For example, if water with a high concentration of salt is put with water with a low concentration of salt, over time these substances will blend to perform a uniform level throughout once the substance passes through a membrane.

How Reverse Osmosis Works

Reverse osmosis relies on a scientific method in which high pressure is used to push water through a membrane that is semi-permeable. The pressure is used to reverse the natural flow that is present in osmosis. Osmotic pressure is used to push the substance through the membrane thus removing various particles and substances you wish to remove. A common usage of reverse osmosis is removing salt from sea water.

Differences Between Filtering and Reverse Osmosis

While this often sounds similar to filtering, it is more advanced than that. Filtration methods typically exclude certain membranes based upon the size of the various particles involved. These particles cannot pass through the filter thereby preventing them from getting into the final substance leaving a purer substance behind. The scientific process that is used in filtration is size exception.

Under reverse osmosis systems the semi-permeable membrane works primarily with pressure that exceeds the normal osmotic pressure which, when applied at different rates, results in the variance in the concentration of solutes to be transferred to the final pure water. This disrupts the normal osmotic process. When a high amount of pressure is applied alongside a high fluctuation of water to a semi-permeable membrane, only the pure portions of the water are able to penetrate the membrane. The remaining insoluble portions are not permitted the time to pass through the membrane and are flushed out of the system before portions are allowed to penetrate the membrane.

Water Purification through Reverse Osmosis

A reverse osmosis system for water purification is typically separate from filtration methods, in practice. Generally, sea water or other brackish water follows several processes to purify it, including reverse osmosis and filtration. Filtration removes larger particles and reverse osmosis completes the filtration process leaving potable water behind. Further, ultraviolet lights are used to further kill any bacteria that may have been able to make it through this process which adds to the purity of the process.


Reverse osmosis thereby provides an alternative method of water purification that is increasing in quality and popularity and increasing the amount of potable water available for consumption.

This article was written by Thomas Jay, professional writer for Sustainable Water Solutions. Thomas is from Orlando, Florida where he lives with his Wife and their two children.

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