Simple and quick guide to understand which is better between RO & UV

At times when we look out for water purifier system, the keywords like RO, UV keep flashing alongside in the details section or on the product image itself. You may consider them as the methods of purification but, what among these two will suit you best is the real dilemma, Right? In this write-up, we are exactly going to explain these keywords, their impacts on water purification and at last the conclusion as which one will be the best fit for you.

Let me draw some points through which we’ll try to understand and find the best method of purification for you.

Reverse Osmosis Methods and its roles

Understand Osmosis first!

By default, water has this natural tendency of flowing from lower level concentration to higher level concentration. So, if you know this then Osmosis can be easily understandable. Osmosis, it is a naturally occurring phenomenon and one of the most important processes in nature. Similarly, like water’s flowing behaviour, Osmosis is a process where a weaker saline solution will tend to migrate to a strong saline solution. We can see various examples of osmosis from our surroundings like pruned fingers (If you’ve ever been in a bath or pool too long, then you’ve seen your fingers and toes get pruned), plant roots absorbing water from the soil and our kidneys absorbing water from our blood.

Image Courtesy- Puretec Industrial Water

Above is a diagram which shows how osmosis works. The movement of one, less concentrated solvent through a semipermeable membrane to another, more concentrated solvent. Speaking of the Semipermeable membrane, what is the role of the semi-permeable membrane? It is basically a membrane that will allow some atoms or molecules to pass but not others. A simple example is a screen door. It allows air molecules to pass through but not pests or anything larger than the holes in the screen door.

Graphic of spiral wound element courtesy of Dow.

For example, if we take a container full of water with a low salt concentration and another container full of water with a high salt concentration and separate them by a semi-permeable membrane, then you’ll see the water with the lower salt concentration would automatically begin to migrate towards the water container with the higher salt concentration.

Now, from the word ‘Reverse’ Osmosis we can clearly get the meaning that it is the reverse of Osmosis. Reverse Osmosis is the process of Osmosis in reverse. While Osmosis occurs by nature without energy required, to reverse the process of osmosis you need to apply energy to the more saline solution. A reverse osmosis membrane is a semi-porous film/membrane that allows the passage of water molecules but not the majority of dissolved salts, organics, bacteria and pyrogens. However, you need to ‘push’ the water through the reverse osmosis membrane by applying pressure that is greater than the naturally occurring osmotic pressure in order to desalinate (demineralize or deionize) water in the process, allowing pure water through while holding back a majority of contaminants.

Image Courtesy- Puretec Industrial Water

The best example of Reverse Osmosis is desalination plants.


A Basic Comparison between RO AND UV Purifier features—


RO Water Purifier UV Water Purifier
Requires Electricity to operate Requires Electricity to operate
Kills and Removes all the Bacteria and Viruses from the Water. Kills all Bacteria and Viruses but their Dead Bodies remain in the Water.
Requires Electricity to Boost the Tap Water Pressure UV Water Purifiers can work with Normal Tap Water Pressure.
Removes the Dissolved Salts Cannot remove Dissolved Salts
Suitable for TDS Level above 350ppm

RO Purifiers has Prefiltration system to work with the Dirty

Water should be clear for UV to work.


RO Function and its limitations

Well, before discussing how RO system works have a quick understanding of how Reverse Osmosis works?

A high-pressure pump increases the pressure on the salt side of the RO and forces the water across the semi-permeable RO membrane, leaving almost all (around 95% to 99%) of dissolved salts behind in the reject stream.

The water that gets demineralized is product/premate water whereas the water that is concentrated or hasn’t passed to the other side of the semi-porous film is called concentrated/reject water that comes out from your RO system in intervals.

Similarly, the RO system smartly separates the product and concentrated water. Well, if we talk in terminology then we can say it functions on cross filtration. Cross filtration is simply a mechanism where a solution(in this case water) passes through the filter, or crosses the filter, with two outlets: from one outlet the filtered water goes one way while from the other the contaminated water goes the other way(which is in normal case from the pipe to your kitchen sink). RO system is built that smart enough that it forces the build-up contaminants to sweep away & allow ample turbulence to keep the semi-membrane surface clean.

Diagram of a Reverse Osmosis System with Basic Components:

Diagram courtesy: esp water products

This was all about RO. You know it’s good for removing heavy metals, but like everything has its own limitations it also has some. In spite of RO processes being an effective one, certain microorganisms like bacteria and viruses manage to sneak through the semipermeable membranes.

The process does not allow any contaminant having a molecular weight exceeding 200 to pass through. Also, it doesn’t allow the atoms with higher valency to pass through which is, in this case, is Sodium.

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 can go with UV filtration to get rid of the residual bacteria and viruses.

The advantage of the UF water purifier is that it works without electricity as well and is sure to filter out any disease-causing germs, including the smallest of viruses. The UF membrane is also so small that it will filter out all dust and other particles and make the water safe to drink.

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 with the highest degree of purity.

The only issue with UF water purification system is the case of highly dissolved salts in the water, which it misses to filter out. Here, RO works well. It can filter out harmful dissolved salts from the water.



See, Reverse Osmosis is an effective and proven technology to produce water for the most demanding applications. It can be suitable for many, those who require demineralized or deionized water, especially the areas having higher TDS Level. It’s effective for removing metal impurities, pesticide residue, and bacteria. But, when it comes to removal of gases and other atoms of higher valency atoms it lags. And, where it lags there come to the UV system. UV system can filter out the microorganisms. It’s best for the areas where there is much of electricity shortage. But, the same thing goes with UV also. It cannot eliminate TDS and heavy metals.

So, cutting long story short, in a line we can say that with the use of both in a system as (RO+UV) you can achieve the highest degree of purification for your drinking water.

A last piece of advice to follow –Proper pre-treatment and monitoring of an RO system are crucial to preventing costly repairs and unscheduled maintenance. With the correct system design, maintenance program, and experienced service support, your RO+UV system will provide many years of high purity water.

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