Water Purification Technologies – RO, UV, UF

Technological advancements in the water purification process has taken greater strides in the last few decades starting from its application in household to large scale water treatment plants.

As an individual, when you decide to purchase a water purifier for your home, you find a plethora of choices available. You have various technologies staring at you.

Choosing the best among water purification techniques like RO, UV, and UF can confuse you. These are different technologies, hence the uses are also different. You should have an idea which of these technologies suits your requirement. Let us look into these aspects. Prior to that, we shall have a brief background to have a clear understanding of the subject.

The Background

The quality of ground and surface water is far from satisfactory today. This is because of the rampant release of effluents and industrial waste into the water bodies. This contaminates the water thereby necessitating the governing municipal bodies to employ measures to purify it before distribution. Chlorination is one of the common methods of water purification employed by these municipal authorities.

Is this enough?

Unfortunately, it is not. You need to employ other means of filtration and purification to make the water safe to drink. The use of RO, UF, and UV water purifiers is one solution to this issue. Let us now look at the salient features of these three methods of water purification. We will also look at the factors that necessitate the use of these purification methods.

Reverse Osmosis (RO)

We shall begin with the most common/popular method of water purification, Reverse Osmosis. One should have a clear understanding of the RO concept. In order to do so, you need to understand the process of osmosis.

Osmosis is a natural process. Water has an inherent property of moving from an area of lower concentration to that of a higher concentration when you separate the liquids using a semipermeable membrane. The absorption of water by the roots of the plant is one of the most common examples of osmosis.

In the RO process, you reverse this property of water. Naturally, you need an external force to do so. Hence, we can say that reverse osmosis is a procedure where the water moves from an area of higher concentration to that of a lower concentration. Now, you need to apply this force at all times to prevent the return flow of water. The desalination of seawater is one example of Reverse Osmosis.

The drinking water sources contain a large amount of visible as well as dissolved impurities. Hence, RO is one of the best methods to separate the impurities from the drinking water source and enabling the supply of pure drinking water. This is an effective purification method as you are able to eliminate 95% to 99% of all dissolved impurities.

The RO Water Filtration Concept

Reverse Osmosis works on a unique concept of cross filtration. This entails the provision of two different outlets, one for the purified water and the other for the elimination of impure water. This water is also known as ‘Reject Water’. The RO process works on the principle of forcing contaminated water through a semipermeable membrane. This membrane can eliminate up to 99% of TDS from the water source.

Advantages and Drawbacks of RO

In the RO purification process, a selective membrane is used and it does not allow contaminants having a molecular weight exceeding 200 to pass through it. Water, having a molecular weight of 18 easily passes through. Most of the contaminants have heavy molecular weight, hence they are eliminated. But, there are contaminants having molecular weight less than 200 and they can still pass through the semipermeable membrane.

RO membrane also allows gases like carbon dioxide to pass through. As stated above, since certain fine impurities and contaminants manage to sneak through the semipermeable membrane, there is a need to use a supplementary system like UV or UF to remove such impurities.

Secondly, the pure water obtained from the RO process contains a very low amount of TDS. You need these salts for enhancing the taste of water. Therefore, you require mineralizers and TDS controllers to supplement the RO system. 

Ultraviolet Purification (UV)

RO is a good water purification process, but it is not the most perfect one. You have seen the shortcomings on the process in the previous paragraph. Certain bacteria, viruses, and microorganisms do manage to sneak through the semipermeable membrane of the RO water purifier. These germs can cause water-borne diseases like dysentery, diarrhea, and typhoid fever. The UV purification system eliminates these germs and bacteria from RO purified water. Therefore, you will usually find the UV system working in close coordination with the RO water purifier system.

How are UV filters different from RO systems?

RO water purifiers have a major disadvantage in the fact that they waste a lot of water. During the process of purification, the proportion of reject water is 3 times that of purified water. In these days of water shortage, this wastage of water is a serious problem. UV water filters do not waste water. They do not make use of chemicals to treat water. Hence, they are useful for maintaining the taste of water. RO filters require a lot of maintenance whereas the UV filters don’t.

The disadvantage of the UV system is that they are incapable of removing TDS like sulphates, nitrates, and fluorides. They do not remove heavy metal impurities like arsenic or lead. Hence, you have to use these filter systems in combination with the RO system for maximum efficiency.

What is Ultrafiltration?

In comparison with the RO membranes, the UF membranes have larger pores. These filters are successful in eliminating bacteria, viruses, and other microorganisms. However, they are not capable of handling TDS and heavy metal impurities. The advantage of using UF systems is that these filters do not require as much maintenance. The UF process is different from UV because it does not use ultraviolet radiation for the purification process. This system does not envisage the use of electricity.

Who should use the RO, UV, or UF filters?

We have seen the process involved in the RO, UV, and UF filters. We are also aware of the advantages and disadvantages of these systems. Let us now look at who can use these filters.

Normally, you should not use these filters in isolation. It is always better to have a combination of all these three filters in a single water purifying machine. The present-day water purifiers adopt this combination of all the three filters. We shall look at the individual uses of these three filters.

I.  Ultrafiltration

Ultrafiltration is the simplest of the three filtration techniques in question. This system is extremely useful for removing visible as well as invisible impurities. Hence, you can use this technique as a sediment filter. The filters based on the gravitational method use this technique. The greatest advantage of these filters is that they are easy to clean. They do not require electricity to work. You can use these filters where the TDS component in the water source is within permissible levels.

The application of ultrafiltration is not limited for household use and is also used for other specific purposes and below listed are some of them.

  1. Wastewater Plants: Wastewater contains large quantities of insoluble and visible contaminants.  Ultrafiltration is perfect to remove these contaminants before subjecting the water to further treatment.
  2. Separating Oil and Water Emulsions: Ultrafiltration techniques are good for separating water contaminated with oil. The oil molecules are bigger than the water molecules. Hence, they cannot pass through the ultrafiltration membranes.
  3. Diafiltration Plants: The ultrafiltration process is also very useful in Diafiltration plants. This system ensures the separation of permeable molecules like salts, other solvents, and small proteins.
  4. Clarifying Juices: The concentrated fruit juices have a high proportion of pectin, fibres, proteins, and starch. The ultrafiltration technique is perfectly suited to clarify fruit juices.
  5. Dairy Products Manufacturing: Removing pathogens from milk and making cheese also requires the use of ultrafiltration techniques.

II.  Ultraviolet Filtration

Ultraviolet filtration techniques are rarely used in isolation. Usually you find a combination of UV and UF or UV and RO. The greatest advantage of UV filtration is that it does not alter the taste of the water. It kills the germs and other microorganisms present in the water source. It does not affect the sediments and other mineral contaminants. This is why you require supplementary filtration methods.

UV filtration has a variety of uses. Let us look at some of them in brief.

  1. Food Industry: The principal advantage of UV filtration is the elimination of bacteria. Hence, you have use for this technique in the food industry to guard the food against waterborne bacteria.
  2. Soft Drink and Wineries: This technique is also used in wineries, breweries, and soft drink bottling plants.
  3. Pharmaceutical and Cosmetic Industry: This technology ensures bacteria-free water for manufacture of medicines in the pharmaceutical industries. Similarly, the cosmetic industry requires pure water for manufacture of cosmetic products.
  4. Laboratories and Hospitals: Hospitals and laboratories require sterilized water for testing of medicines and equipment. This is an effective quality control measure.
  5. Homes, Schools, Offices, and Hotels: UV technology is the simplest way to get bacteria-free water. This technology is very useful in places where the TDS levels of the water source are within acceptable limits. When used in combination with UF or RO technology, you get pure water of the highest quality.
  6. Wastewater Treatment Plants: This technology is extremely useful as a secondary treatment of wastewater before releasing it into the sea. This process kills the germs and pathogens thereby helping to preserve marine life in the receiving waters.
  7. Swimming Pools: Water when treated with UV radiation allows the user to reduce the chlorine treatment. This helps control the growth of algae and slime.
  8. Ranches: Providing UV treated water to the farm animals help in improving the quality of the yield.

III.  Reverse Osmosis

We have already seen the concept of RO. The major beneficiary of the RO water purification system is the domestic use. You can find RO water purifiers in practically every home. But, the home water purification system invariably is a combination of RO technology along with either UV/UF or both UV and UF. In fact, you have six-stage filtration processes in the home water purifiers. They include the sediment filter and the pre and post activated carbon filters.

Other than providing pure drinking water, RO systems have various uses such as,

  1. Wastewater Treatment Plants: The semipermeable membrane used in the RO process ensures the elimination of visible as well as dissolved impurities.
  2. Desalination Plants: Some countries in the world such as the United Arab Emirates do not supply fresh groundwater. They have to depend on desalination plants to obtain fresh water from seawater. These seawater desalination plants work on the RO technology.
  3. Food and Beverage Industry: This industry needs good quality water. The RO systems are the right ones to provide water of the highest quality.
  4. Power Generation: Water is the main source for generating electricity. Water with a high proportion of sediments and other contaminants can affect the power generating equipment. Subjecting the water to RO treatment before use is extremely beneficial.
  5. Commercial and Industrial Operations: RO systems are of great use in industries. One of the principal uses is the pre-treatment of boilers and coolers. RO water has utility in water jet cutting or machining to cut soft non-metallic materials.
  6. Pharmaceutical Industry: This industry requires pure water for manufacturing medicines. RO technology in combination with UF and UV can provide perfect quality.


We have seen three common methods of water purification and their utility in various industries. The principal utility is for purifying drinking water. It is always beneficial to have a water purifier that uses all the three technologies, RO, UF, and UV for purification. These three technologies work in perfect coordination by cancelling out each other’s weaknesses. Hence, the ultimate beneficiary is the consumer who gets pure water of the highest quality to drink.