What is RO Water Purifier? Working, Benefits & Limitations

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In Brief: What is RO Water Purifier

An RO water purifier uses reverse osmosis to treat water. It can remove several types of impurities from water, including TDS and heavy metals. It uses external pressure to push water through a semipermeable TFC membrane. The pores of the membrane are small enough to retain all kinds of contaminants. A big drawback is that these water purifiers produce a lot of wastewater.

The water supplied to most houses isn’t meant to be consumed without some kind of treatment. This is because water passes through many channels before it reaches our homes.

This exposes it to countless contaminants that can be harmful if not removed. There are many different ways of purifying water to make it potable. [1]

RO water purifiers are one of the most commonly opted solutions for drinking water. But what makes an RO water purifier different from the other types of filtration systems available?

What is an RO Water Purifier and How it Works

An RO water purifier uses the technique of reverse osmosis to remove contaminants from water. [2]

Such a purifier can remove impurities like TDS, microorganisms, metals, chlorine, fluoride, and VOCs.

This process is called reverse osmosis because it applies pressure to overcome the natural osmotic pressure. Osmosis occurs when there is a chemical potential difference in a solution separated into two by a semipermeable membrane.

Normally, the part with more water and fewer impurities pushes water into the part with less water and more impurities.

In RO, an external pressure overcomes this flow, making all the water go past the membrane to the other side.

The RO membrane is a special thin composite film (TFC) membrane with extremely minute pores. These pores, being 0.001 micrometers in size, are too small to let the impurities pass through. [3]

As a result, only pure water flows past the membrane, thus making it potable.

The RO membrane is the core of these purifiers but an RO system has multiple stages leading to this. First, the feed water flows through a sediment filter that removes particles like dust, dirt, sand, and rust.

Next, an activated carbon filter takes care of volatile organic compounds (VOCs), chlorine, and substances causing bad smell or taste. [4]

Finally, the water flows through the TFC membrane where 98% of total dissolved solids (TDS) are removed.

The sediment filter and activated carbon filter together form the pre-filtration stages. Some RO systems come augmented with post-filtration stages like UV, post-carbon, and re-mineralization stages.

In most RO systems for home usage, the RO membrane comes in a cartridge. Inside this cartridge are layers of the TFC membrane wrapped in concentric circles around a core tube.

The purified water flows through these layers into the core tube. Whatever water does not flow in this tube, flows out of the system concentrated in all the impurities.

This wastewater is usually two or three times the amount of purified water. There are ways to reduce the amount of wastewater such as using a permeate pump or shutoff valve.

Watch this video to see a visual demonstration of the RO water purification process:

Benefits of an RO Water purifier

The biggest advantage of using an RO water purifier is that it can remove a wide variety of impurities from water.

This includes salts and TDS, something that other water purification systems are not capable of.

It manages to do this without using any chemicals for water treatment. The RO water purifier is very easy to use. Installation is also quite basic as the system has a modular design.

The purified water has minimized TDS levels, which makes it taste better.

This also makes food and beverages taste better when the purified water is used in cooking. Another advantage is that reverse osmosis is more energy-efficient than the process of distillation.

Limitations of an RO Water Purifier

One drawback that keeps buyers from opting for RO water purifiers is the wastewater production.

Usually, the amount of water wasted is 50% or more of the feed water. This is not good for the environment as water is a precious commodity.

Reverse osmosis requires high water pressure to be maintained.

This external pressure is supplied through a pump which requires electricity. As compared to water purification systems that run on little to no power, this is a blatant con.

The RO purifiers are also known to strip down the TDS to a very low level, thus making water quality unacceptable. This problem is generally taken care of by adding back TDS in later steps of purification or using a MTDS.

An RO water purifier will need regular maintenance to clean the system and prevent clogging.

The filter cartridges will also need to be replaced periodically. These cartridges need to be disposed of responsibly as they are highly non-biodegradable.

Other than being unsustainable for the planet, there is only one other problem with an RO water purifier.

The purification procedure is time-consuming and can take up to 20-30 minutes for one tank to fill up.

When to use an RO Water Purifier

An RO water purifier is ideal when the water supply has very high TDS levels. TDS or Total Dissolved Solids comprise a long list of impurities that cannot be filtered out by other water purifiers.

High levels of TDS affect the aesthetics of water and a level over 900 PPM makes water unfit for drinking.

RO water purifiers are also a good option if the feed water contains heavy metals like lead and copper. Contaminants like these can have serious detrimental effects on health.

This is especially so for children whose immune system is still developing.

When combined with a UV filter, an RO water purifier is great for removing microorganisms in water. Together, they not only kill pathogens like bacteria and viruses but also filter out the carcasses.


An RO water purifier uses reverse osmosis to filter out a wide variety of contaminants. These include bacteria, chlorine, fluoride, heavy metals, insecticides, pesticides, TDS, salts, and more.

It does this by using external pressure to push water through a special TFC semipermeable membrane. The filter pores are so small that only the water passes through them and the impurities stay back.

The end result is purified water fit for consumption. RO water purifiers are very easy to use and install. They are more energy-efficient than a distillation apparatus. But they need electricity and high water pressure to operate.

The biggest problem with using an RO system is wastewater production.

The amount of water wasted is often 50% or more of the feed water. Nevertheless, an RO water purifier is a good treatment option for water comprising high TDS, heavy metals, and pathogens.