How Does Reverse Osmosis System Works

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Reverse Osmosis (RO) is commonly used in water filtration systems. But what is it and how does reverse osmosis system works? To know more about reverse osmosis, let understand the process of osmosis.


Osmosis is a natural process which allows a less solvent solution to moved to a higher concentrated solvent through a semi-permeable membrane. It is the most important natural process in the world. Some common examples are our skin will be puffed when showering too long and the absorption of water in the plants root.

Let’s take bathing as an example. When you are in the bath tub for long, your skin will tend to be puffed. Your skin is acting as the semi-permeable membrane where it allows water to pass through. That is osmosis.

What is semi-permeable membrane? Imagine the membrane as a thin layer film that has millions of hole in it. The diameter of the hole can be as fine as 0.25 micron which is 200 times finer than the diameter of an average human hair. Majority of the concentrated saline will not pass through the membrane.

Reverse osmosis is the opposite of the osmosis process. Reverse osmosis allowed more concentrated saline passing though a less solvent solution with a little pressure. This will allow up to 99% of the contamination such as minerals, bacteria, and salt to be left behind.

Below is the diagram of the process of reverse osmosis. When forces is applied at A, the more solvent area, B will be push towards the membrane, D and go to a less concentrated saline, E leaving behind the particles at C. Reverse Osmosis Diagram

A: Pressure Applied ;                         B: Concentrated Solution ;              C: Particles Left Behind
D: Semi-permeable Membrane ;     E: Less Concentrated Solution ;      F: Less Pressure Area

Is Reverse Osmosis water good or bad for health?

There are contradicting information on the benefits and drawbacks of different types water filter. This is due to some irresponsible sites or company trying to belittle a particular types of water filter to make their product stand up which is annoying and often confuse readers.

Water Quality Association (WQA) is the best reference on water related issue. They are a non-for-profit organization that provides accurate information and certified products in the market. This is a go-to place if you have any doubts on any types of filtration system.

Reverse osmosis water removes up to 99% of the minerals no matter is beneficial or harmful. Often people will argue on the removal of beneficial minerals such as calcium and magnesium which is a loss to our body.

According to WQA, reverse osmosis water is safe to consume. The loss of minerals is simply negligible as the quantity is small if it is compare to the food minerals that are consumed. Drinking water with

In the argument of reverse osmosis is more acidic, the pH is not acidic by a lot as compare to orange and lime juice. Based on the research from WQA, when the water in contact with saliva, the pH different can be ignore as it will neutralize.

Reverse Osmosis Water Filter System Are Normally Multi Stage Filters

Most of the reverse osmosis water filter in the market are multi stage filtration system. It comprise of at least 3 different segments.

Stage 1 : Pre-filter
It is normally sediment filter which removed foreign particles that mostly able to be seen from a naked eye such as dirt, sand and rust.

Stage 2 : Carbon Block Filters
There are normally multiple stage 2 filters which removed different types of minerals using carbon block filters. Carbons which is often used as filters to get rid of chlorine, lead, asbestos and other harmful minerals.

Stage 3: Reverse Osmosis membrane
After at least 2 stages of filtering, it will be channeled to the membrane to perform reverse osmosis to filter up to 99% of the contamination.

Some filtration system will have optional stages where they change the pH and adding beneficial minerals in to the filtered water. In my opinion, it is not necessary, but it is a plus point to have additional good minerals in the water.

The diagram below is explains how reverse osmosis water filter system works in one of the best seller filter in Amazon. iSpring RCC7 Reverse Osmosis Filter System receive a Gold Seal Certification from WQA.

iSpring Reverse Osmosis System


Is it Guaranteed up to 99% removal of minerals ?

Well, there is no guaranteed for 99% of removal for every minerals from all companies. Some of the product in the market have certifications from WQA on the minerals that is filtered which proofs their claims.

The diagram below is the minerals that was removed by APEC ULTIMATE RO-90 Multi Stage Reverse Osmosis Filter. The minerals listed below are just a portion of the minerals that are tested and certified by WQA and is not the complete list.

Certified Mineral Removal by WQA

Water filters are not required to be certified by WQA in order to put on the shelf. Hence, It should not be the only requirement of consideration on buying a water filter. However, it is an advantage if a product is certified. You can always refer to WQA whether a model that you purchase is WQA certified.

Maintenance & Replacement

Maintenance is a big part in making sure that the membrane can last longer without getting a replacement. Depending on the usage of the water, cleaning the membrane should be done every 4-6 months. If the water pressure is getting low on the faucet of the system, it is time to do some cleaning

Some system are having a backwash mechanism where it can do the self cleaning without removing the membrane while some required manual cleaning by pushing water across the membrane in the other direction.

To save the hassle of cleaning, you can hire a service company that specialize in cleaning the filtration system. The cleaning done offsite are often better than those that done onsite. They have proper cleaning tools to thoroughly clean your systems.

A normally reverse osmosis membrane typically can lasts for 3-5 years while still retained the filtering capability between 90%-99% if you are constantly cleaning the membrane.

Reverse Osmosis water is by far the cleanest water that are suitable for human consumption. Although the price might be a little high, it is still worthwhile to invest on clean water for your family.

You can also check out here on what are the available options of water filters if budget is a concern to you.

Are you ready to own a reverse osmosis system?



6 thoughts on “How Does Reverse Osmosis System Works”

  1. What a great informative site. I had no idea all the steps it took for reverse osmosis, Definitely made me rethink where I get my water from. What system would you recommend?

    • Dale, if you have a small family (less than 6) in a house, I will recommend you to check out the APEC ROES-50 as a start. This model is capable of producing 50 gallons of pure water daily. If you have a bigger family (More than 6), probably you can consider the iSpring RCC7 which is able to produce 75 gallons of pure water per day.
      In my opinion, both models are consider the entry models for RO water filters. Hope this helps.


    • Those model are just for drinking water only. There are only a handful of models in the market which is using RO on whole house water filter. In my opinion, it is not very cost effective to have whole house water filter on RO. A normal sediment filter with carbon blocks should be sufficient.


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