How Does Reverse Osmosis System Work? And What are the Benefits?

Before digging into the whole process of “Reverse Osmosis” one must know about the naturally occurring process of osmosis that how it works.


How Does Osmosis Work

Osmosis is one of the most important and naturally occurring processes among all that takes place in nature. In this process, a saline solution which is weaker in concentration moves towards a strong saline solution. Example of this process includes when plant roots absorb water from the soil for better growth and nourishment of plant.

Reverse Osmosis:

Now let’s talk about the term Reverse osmosis. This process is just the reverse of the naturally occurring “Osmosis” process. Osmosis occurs without the use of any kind of energy, but in the case of reverse osmosis, energy is required for the completion of the process. It contains a reverse osmosis membrane just like a semi-permeable membrane which is responsible for allowing the water molecules and stopping the entry of dissolved salts, bacteria and organics.

The pressure is applied to push the water against the membrane so that water can pass through.  The applied pressure must be higher than the naturally occurring pressure in simple osmosis process to demineralize the water in the whole procedure to get pure water and to hold the impurities.

How Does Reverse Osmosis Work?

In reverse osmosis, a high-pressure pump is used to increase the pressure on the salt side of the RO as well as force the water across the semi-permeable membrane, which leaves almost 99% of the salts back into the stream called as reject stream.  Now the amount of pressure required is not fixed here but depends on the salt concentration of the feed water. If the salt concentration is higher in the feed water then obviously pressure required would also be high and vice versa.

Reverse Osmosis Function

The demineralized water is known as permeate or product water, and the water stream that contains all of the concentrated salts or contaminants that fails to pass the membrane is known as the reject stream.

As the feed water enters into the RO membrane under an absolute pressure, the water molecules successfully pass through the semi-permeable membrane. On the other hand, the contaminants and many different salts that are not allowed to pass through it get discharged through the reject stream which is further sent to the drain system for recycling. The water that makes it to the RO membrane is termed as the product water with almost 95-99% impurity removal rate.

Here it is essential to understand that the RO system employs a process of cross filtration as compared to the standard filtration process. In the process of cross filtration, the solution is passed through the filter having two different kinds of outlets:

Filtered water moves to one way.

Contaminated water moves towards the other way.

Now to avoid the contaminants buildup, a process called cross-flow filtration is used that allows water to remove all of the impurities and prevent the contaminants build up.

Benefits of Using Reverse Osmosis System

Reverse osmosis helps in improving the taste of water

The reverse osmosis process helps to improve the taste, appearance as well as the odor of water by removing all of the contaminants that are not safe for human consumption.

Simple maintenance

RO system is quite easy to maintain. Its parts are easily removed for the cleaning and maintaining purposes.

Saves money

You must be thinking about how it can save money?

Many people purchase bottled water from markets as it is safe and pure, but the reverse osmosis filtration technique also provides clean and clear water which is way better than the bottled water.

Removes impurities

RO system removes several different pollutants from the water like pesticides, bacteria, arsenic and much more. RO systems now can also remove the excess amount of chlorine from the water which is not safe for human consumption.

RO Pretreatment

Pretreatment is necessary to prevent fouling, scaling and the chemical and mechanical damages.

Fouling is due to the accumulation of contaminants on the membrane surface that results in the blocking of the membrane.

Scaling is also something like fouling, but it is because of certain compounds that exceed their solubility limits and buildup on the RO membrane. This also results in the plugging of the membrane.

Chemical attack damages the membrane by using the chemicals like chlorine and chloramines.

The mechanical attack also plays its part in damaging the RO membrane. The mechanical damage is caused due to the excess amount of pressure exerted.

Multi Media Filtration

It uses the filter which consists of three layers: anthracite coal, sand and garnet and with a supporting layer of gravel at the bottom.


The filter used in this type of filtration has a pore size of 0.1-10um. It is best for the removal of colloidal and bacteria.

Sodium Bisulfite (SBS)

By adding sodium bisulfite in water before an RO membrane, it will remove residual chlorine.

RO membrane cleaning

It is the periodic cleaning of RO membranes like 3-4 times in a year, depending on the feed rate.

Factors that Can Affect the Performance of Reverse Osmosis Technique

  • Water temperature affects this technique as the cold water may take more time.
  • The pressure of the incoming water also affects the RO performance. If the pressure is too low then obviously the RO system will fail to work properly.
  • Another factor that declines the performance of the reverse osmosis technique is the use of different kind of membranes. Their quality should be good enough to deal with the contaminants perfectly.
  • Different kind of solids dissolved in the tap water.

Clean Water Supply

Every human being has a complete right to drink safe and clean water as it saves a person from a different type of diseases. Reverse osmosis technique has made our lives much better. If you properly take care of an RO system, it can last for almost 10-15 years but here lies a promise that you should clean it annually and the membranes should be changed as soon as they get damaged. It is highly recommended that you should install the RO system in your home to know the taste of the best-treated water.

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