As you browse through the different types of water purification systems available on the market, you will frequently come across the words ‘Reverse Osmosis’ and ‘Ultraviolet Purification’.

What is the difference between these two methods? Let us look into these aspects in the following paragraphs.

Reverse Osmosis Method

In order to understand this process, you should be conversant with the Osmosis process. Liquids have a natural tendency to move from a level of lower concentration to a higher concentration through a semipermeable membrane. Plants absorbing water from the soil through the roots is the simplest example of osmosis.


Now, reverse osmosis is the reverse of the osmosis process. Hence, there is a flow of liquids from a level of higher concentration to a level of lower concentration, again through a semipermeable membrane. Naturally, you need to exert additional external pressure for this process to function.


The best example of this technique is the desalination plant. The RO water purifiers at home also function on the same principle.

The role of the semipermeable membrane

The semipermeable membrane mechanism is the defining factor in any RO process. This mechanism allows certain molecules to pass through while restricting the others depending on their size.

Secondly, it does not allow the reverse flow of liquid as well as the molecules. One simple example is the window screens. They allow the air to circulate while restricting the insects and larger visible impurities.

RO Water PurifierUV Water PurifierUF Water Purifier
Requires Electricity to operateRequires Electricity to operateNo Electricity required
Kills and Removes all the Bacteria and Viruses from the Water.Kills all Bacteria and Viruses but their Dead Bodies remain in the Water.Kills and Removes all the Bacteria and Viruses from the Water.
Requires Electricity to Boost the Tap Water PressureUV Water Purifiers can work with Normal Tap Water Pressure.UF Water Purifiers can work with Normal Tap Water Pressure.
Removes the Dissolved SaltsCannot remove Dissolved SaltsCannot remove Dissolved Salts
RO Purifiers has Prefiltration system to work with the Dirty Water.Water should be clear for UV to work.Works with Dirty Turbid Water.

How does RO function?

Reverse Osmosis functions on the principle of cross filtration. The feed water passes through the RO membrane where the TDS and other harmful metal impurities are eliminated thereby purifying the water.

The cross filtration method has two outlets. One outlet is for the reject water that contains a high concentration of impurities and TDS. The other outlet is for the pure water.

Reverse Osmosis is an effective system of purifying water, but it has its limitations. The process does not allow any contaminant having a molecular weight exceeding 200 to pass through.

At the same time, it does not allow ions having high valency to pass through. Sodium is a monovalent ion.

Therefore, the RO membrane does not restrict sodium ions. In the same way, the RO membrane fails to restrict gases like Carbon Dioxide. Similarly, it does not restrict all kinds of bacteria and viruses. You need UV filtration to get rid of the residual bacteria and viruses.

In spite of RO processes being an effective one, certain microorganisms like bacteria and viruses manage to sneak through the semipermeable membranes.

Hence, you find most of the RO filters having UV chambers for eliminating these microorganisms. UV filtration can remove 99.9% of microorganisms. Hence, you get water of the highest degree of purity.

Which of the systems is better, RO or UV?

Definitely, RO is the better one because this process can remove Total Dissolved Salts, heavy metal impurities, pesticide residue, and bacteria. On the other hand, the UV system does not eliminate TDS or other impurities. It can eliminate the microorganisms alone. Therefore, it is always better to use both the systems in combination rather than in isolation.

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