What is reverse osmosis? How Does the Reverse Osmosis Process Work?

by | Oct 30, 2023

What is reverse osmosis

Are you looking for a water purifier for your home? If so, you might be wondering what exactly reverse osmosis or RO is. Well, the answer is hidden in your high school biology textbook. Are you starting to remember something now?

In this article, we will discuss reverse osmosis or RO filtration technology in detail so you can decide if your home requires RO water purification without going back to high school science class.

What is Osmosis?

Osmosis is the movement of a fluid through a filter, known as a semipermeable membrane, from an area of high fluid concentration to an area having a lesser fluid concentration.

Scientifically speaking, Osmosis is the movement of a solvent through a semipermeable membrane from an area of low solute concentration to an area of higher concentration. In biological systems, the solvent is typically water, but osmosis can occur in other liquids, supercritical liquids, and even gases.


What is Reverse Osmosis?

Reverse osmosis is the movement of a fluid through the semipermeable membrane from an area of low fluid concentration to an area with a higher concentration. In simpler terms, it is the exact opposite of osmosis.

Reverse osmosis is the most effective water filtration method as it pushes water through a microscopically small filter material. Chemical or carbon filtration systems, on the other hand, use specific materials to attract or directly target the contaminants in water.

CC: Chemical Engineering World

Principle of Reverse Osmosis:

Filtration is the main principle of Reverse Osmosis. When water is passed through the semipermeable membrane by applying pressure, solid impurities aren’t allowed to pass through due to the minimal size of the pores in the membrane.

When this happens, the water molecules start concentrating on one side while the other side of the membrane becomes dilute.

Roughly, reverse osmosis occurs when the water passes through the membrane against the concentration gradient. It moves from a higher concentration to a lower concentration.

How Does Reverse Osmosis Work?

Reverse Osmosis works in a way similar to osmosis but precisely opposite. We have already discussed osmosis earlier in this article, so let us jump straight into the workings of reverse osmosis.

In Reverse Osmosis, pressure is applied to the water to overcome the osmotic pressure and push it from a high to a low concentration of contaminants. The water is forced reversely, and the contaminated water is converted into pure water. 

As the water passes through a filter, the contaminants are stopped, and only pure water passes through. This results in the cleanest possible drinking water – precisely what we want!

Reverse osmosis involves four stages of filtration: 

1. Sediment Filter

The sediment filter removes the most oversized particles to prevent clogging of the subsequent filters.

2. Pre-Carbon Block

The pre-carbon filter utilises activated carbon to prevent particles more significant than a particular size (in nanometers) from passing through. It also attracts and bonds with positively charged ions to prevent compounds like chlorine and chloramines from passing through to the third filter.

3. Reverse Osmosis Membrane

The reverse osmosis membrane removes all molecules weighing more than water, such as sodium, high levels of lead, dissolved minerals, and fluoride.

4. Post-Carbon Filter

The post-carbon re-filters the water.

What Are The Benefits Of Using Reverse Osmosis For Water Purification?

Reverse Osmosis technology is the best when it comes to the purification of water in homes as well as at industrial scale.

Here are the main benefits of using reverse osmosis for water purification:

1. Removes contaminants

RO can remove impurities like chlorine, lead, arsenic, nitrates, and fluoride. This can result in water that is cleaner and purer, with a crisp, refreshing taste.

2. Better-Tasting Water

RO can remove 95-99% of total dissolved solids (TDS) from drinking water. It can also filter out bacteria because they are too large to pass through the membranes.

3. Simple Maintenance

RO systems are easy to maintain. You simply change the filters and membranes according to your system’s manual.

4. Environmental benefits

RO systems produce less hazardous wastewater because they don’t require any harmful chemicals.

5. Ultraviolet purification

Most RO water purifiers feature a UV chamber that neutralises remaining bacteria and viruses in the water.

What Are The Advantages And Disadvantages Of Reverse Osmosis?

The advantages of reverse osmosis far outweigh its disadvantages. Here are some of them:


1. Cost-Effective

After investing in an RO purifier, you no longer need to bear the high and regular bottled water costs.

2. Effectively Treats Hard-Water

Hard water c contains calcium, magnesium, and other minerals. One of the main benefits of RO water is that it treats hard water, making it safer to consume.

3. Removes Heavy Metals

RO purifiers can remove all sorts of impurities, including heavy metals, from the water, which technologies like UV and UF cannot.

4. Sustainable Alternative To Bottled Water

Reverse osmosis is an excellent alternative to bottled water, which mostly comes in plastic bottles which are harmful to the environment.


1. Wastes More Water

RO water purifier uses more water than it produces. Relatively much water is flushed out during the purification process as wastewater.

2. Removes Essential Minerals

Reverse osmosis removes more than 95% of all pollutants in drinking water, which may include essential minerals. This has been a matter of dispute among various experts.

3. Doesn’t Kill Bacteria And Viruses

RO system can only deny entry to bacteria and viruses and not kill them. If, by chance, these microorganisms pass through the RO system, they can cause life-threatening diseases.

4. Causes Pressure Drop

Many people using RO systems experience a reasonably significant pressure drop in their water flow.

Summing Up

Reverse osmosis technology, known as RO, is the best to purify water at any scale. The simplicity and cost-effectiveness of RO have made it the preferred choice for all sorts of fluid purification applications.

Now that we have refreshed your high-school chemistry memories, you must quickly get a safe and sustainable water source through an RO!!

Bhuwan Bhatia

Bhuwan Bhatia

Bhuwan Bhatia, an engineering graduate with a diverse background, has been passionate about entrepreneurship since age 13. Founder of edtech startup Technoshaala, Bhuwan now focuses on leading his innovative water management startup, FLOTAA, in Kanpur to create sustainable solutions.
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