Chemistry Behind Reverse Osmosis Water Purification


Water is the most essential component of earth and a medium that supports living. Unfortunately, increases in natural calamities, like floods and droughts and man-built water pollution has disturbed the water levels, leading in scarcity of pure drinking water. Scientists and environmental experts are constantly searching for different water purification processes that can provide safe and pure drinking water for the humanity. One of the most reliable, tested, trialled and preferred water purification processes is Reverse Osmosis. It is worth and essential for the current user and future generations to have an in-depth insight on the chemistry behind reverse osmosis and its successful use in water purification.

Reverse Osmosis

Reverse osmosis water or more commonly known as RO water is the most acceptable water used in home and offices. First introduced in 1970s, the Reverse osmosis quickly gained trust and acceptanreverse_osmosisce from millions of users. In fact, various water treatment plants, bottled water companies and commercial water systems worldwide rely on science of reverse osmosis for water purification processes. It becomes highly essential to make the process of reverse osmosis water purification transparent to its end user.

In a layman language, Reverse Osmosis comprises of 2 words, “Reverse” and “Osmosis”. The power and chemistry behind these two can convert sea saline water to drinking water, which is a remarkable achievement for humanity. The chemistry behind the reverse osmosis says that Osmosis allows diffusion of water or dissolved solvents across a semi-permeable membrane while blocking the movement of dissolved solutes. Osmosis involves the movement of solvent from a solution of low concentrated solute via a semi permeable membrane to a higher concentrated solution, thus weakening the high concentrated solution.

Almost all RO water purification companies use this science for producing pure water. Household RO water purifiers work on the same principle, i.e. Forcing water via a semi permeable membrane filtering larger water contaminants. Smaller contaminants remain back mixed with drinking water. Reverse osmosis water purification mostly removes all unhealthy contaminants, such as Sodium, Arsenic, and Copper, Nitrates, Lead, additive Fluoride and even some organic chemicals. Absence of Reverse osmosis purification can lead to some of the most toxic disease, which can result in cognitive and orientation issues.

The contamination removal efficiency is dependent on the rejection percentage, and incoming pollutant concentrations for making drinking water safe. Apart from the membrane, an effective Reverse osmosis purification system must contain:

  • A pre-filter that can remove first stage fouling agents, like rust and lime.
  • An activated carbon post-filter that can essentially remove odor, residual taste, and small compounds left after membrane filtration.
  • Purified water storage tank and automatic shut-off valve when storage is complete.
  • An outlet to drain carrying waste water.

RO water purification systems also need regular maintenance and time to time replacement of components. A semi-permeable membrane needs replacement mostly after 3 years, and pre-filters and post-filters should be replaced regularly depending on water usage, quality, and concentration of contaminants, rejection percentages, and activated carbon removal efficiency. Reverse osmosis purification can generate a large amount of contaminated waste water. High pressure difference across the membrane will generate only small wastage, so RO with high pressures should be preferred. The RO water is mostly below the pH levels of 7 so it might produce acidity and tasteless for some.


Reverse osmosis is not successful in removing a variety of contaminants (VOCs) dissolved in water, organics, in-organics, particulates and bacteria that are high in contaminated water. The purified water accumulates on one side of a semi-permeable membrane. This water then can directly be used in homes or stored in RO bottled water plants. However, it is to be noted that Reverse osmosis cannot remove all the compounds efficiently. The efficiency of an RO water purification system will also be dependent on the levels, chemical properties and concentration of contaminant molecules. The chemistry behind the reverse osmosis clearly indicates the selection of only effective RO water purification process for safeguarding the health of loved ones.

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