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What are RO (Reverse Osmosis) Water Purifiers? Pros & Cons

Reverse Osmosis Purification

In this age where we have polluted water, air and even vegetables and fruits. So it is essential to employ some form of purification before consuming all of them.

When it comes to water, there are many methods to do purification. RO purification is one such well known method.

In RO purification, water will be desalinated by the process of Reverse Osmosis. This involves forcing salt water to pass through a membrane that has pores to small to allow salt to pass through. It involves fairly high pressure across the membrane.

What is Reverse Osmosis?

Do you know what is the meaning of osmosis?

Osmosis process
Osmosis process

Liquids, especially water have a natural tendency to move from an area of lower concentration to a higher one when separated by a semipermeable membrane. The absorption of water by the roots of the plants is the best example of osmosis.

Then, what is reverse osmosis?

Reverse Osmosis(RO) process
Reverse Osmosis(RO) process

Reverse osmosis is the exact opposite of osmosis. In this process, the liquid moves from an area of higher concentration to that of a lower one, again through a semipermeable membrane. This is against their natural tendency.

Hence, you need to apply force. One of the best examples that come to mind is the desalination of water.

The role of the semipermeable membrane is very important in Reverse Osmosis. This membrane performs a selective role in the sense that it allows some molecules to pass through while restricting the others depending on their size.

Most of the houses have screen doors that allow air to pass through but deters the insects like flies and mosquitoes.

The semipermeable membrane is similar in many aspects. The best quality of the semipermeable membrane is that it allows for the flow of liquid in a single direction. This is because of the force you exert during reverse osmosis.

Reverse Osmosis is extremely useful for separating pure water from other solvents. It also helps in the elimination of dissolved solids in water whereby you get pure water to drink. RO forms the core aspect of most of the water purifiers in the market. Let us look at how RO water purifiers work.

Principle Behind RO Water Purifiers

In a normal filtration process, you see the collection of impurities on the filter media that you have to discard before reusing it.

This process requires frequent maintenance. The RO water purifiers work on a different concept known as cross filtration.

This concept provides for using two outlets. One is for the pure water to flow through whereas the other outlet caters to the elimination of contaminated water, also known as reject water in industry circles.

pH scale chart
pH scale chart

This reject water contains an overwhelming 93% to 95% of impurities.

Some people advocate recycling this water back into the filtering machine. However, that can cause a strain on the machine especially if the concentration of contaminants is high.

You can either drain this water out or use it for alternative purposes such as washing toilets, floors, etc.

An efficient RO system can eliminate 99% of TDS (Total Dissolved Salts), molecules, ions, and also impurities like viruses, bacteria, and pyrogens.

In the normal course, contaminants having a molecular weight in excess of 200 do not pass through the RO filters.

To put things in proper perspective, water (H2O) has a molecular weight of 18. At the same time, the RO filters do not allow ions of higher valency to pass through. Now, sodium is a monovalent ion.

Therefore, sodium ions pass through the RO filters necessitating the use of supplemental filters to eliminate such ions.

RO filters can take care of the heavy metal impurities but allow gases like Carbon dioxide (CO2) to pass through.

Hence, you find RO treated water as slightly acidic with pH value below 7. It is a very effective method to treat groundwater having a high concentration of TDS.

Different Components of RO Water Purifier

You have decided to purchase an RO water purifier system. Therefore, it is important you know the various components of an efficient RO system.

Inlet ValveSediment FilterPre-activated Carbon FiltersRO Membrane
This valve fits into the water source, your tap. You have a tube that attaches to the sediment filter.
This is the first stage of filtration. Your water source can contain visible contaminants like sand, dirt, etc that could clog the RO system. Passing the water through this sediment filter ensures the removal of such visible impurities.
Chlorine is an important ingredient in almost all municipal water sources. This chlorine can damage the RO membranes. Hence, you need to eliminate chlorine from water. The pre-activated carbon filters help you in doing so.
This part of the machine consists of the RO semipermeable membrane. The majority of the impurities are eliminated at this stage.

However, as stated earlier some contaminants like certain bacteria and microorganisms do sneak through the RO membranes. You need supplemental filtration methods like Ultra Violet (UV) and Ultrafiltration (UF) to ensure maximum purification.

UV filters help in removing bacteria and microorganisms whereas UF filters remove the remaining traces of contaminants.

The next stage of water purification involves passing of this filtered water through activated carbon filters to remove any unpleasant smell that remains after the filtration process.

The RO filtration can remove many vital minerals from the water. Hence, the final stages of water purification involve the use of mineralizers to enhance the mineral content of water.

Raw water to mineral water mechanism
Raw water to mineral water mechanism (ref:

The filtered water then passes on to a storage tank for human consumption.

There is an automatic Shut-Off valve that ensures to switch of the flow of water into the tank. This triggers a process whereby the system shuts off. As you consume the water from the tank, the pressure inside the tank reduces thereby activating the machine again.

The impure water or the reject water is drained off through a separate outlet.

The machine has a check valve that prevents the backward flow of water from the storage tank. Similarly, you have flow restriction to maintain the pressure on the inlet side of the membrane. This is to prevent wastage of water.

What is Reverse Osmosis Water Purifier?

A Reverse Osmosis Based Water Purifier Does not use any Compounds or Light to Purify the Water. The RO Purifier uses a Very Fine membrane up to a few microns to purify the water by hindering the impurities to pass through the membrane.

The Membrane in a Reverse Osmosis Purifier is what makes the RO Purifier Stand Out in the Crowd and makes it the Best Water Purifier for Home Purpose. The Membrane present in the RO Purifier can also remove the Dissolved Salts in the Water, which is not possible in other types of water purifiers.

The RO Membrane is capable of removing impurities like Dust and Mud from the water.

All the Bacteria, Viruses, Cysts, toxic antibodies, fluorides and Dissolved Salts like Arsenic, lead, iron and cadmium are removed from the Water.

If you live in an Area where the TDS levels in the water are high, you must consider buying an RO Water Purifier.

The Dissolved Salts like Arsenic, Lead are more Dangerous than the Bacteria and Dust. These are the Heavy Metals which Doesn’t show an immediate effect, rather they act like a slow poison and affect your health in the long term and can cause severe health issues like cancer and nerve damage.

Children are most affected than the adults by the TDS present in the water.The Heavy Metals I have mentioned above have 5 Times more Gravity than that of the Water.

  • Arsenic – 5.7 grams per cubic cm
  • Mercury – 13.546 grams per cubic cm
  • Cadmium – 8.65 grams per cubic cm
  • Lead – 11.34 grams per cubic cm

As I mentioned earlier, these Dissolved Poisonous Salts can be removed only by the RO Water Purifiers.

Reverse Osmosis Water Gives the Safest Drinking Water even with the Water that has High TDS levels.

Please note that a Normal RO water Purifier can not clean the Water that has TDS levels in Thousands.Note: Do not buy Cheap or Unbranded RO water purifiers. These types of water purifiers will remove all the dissolved salts from the water including the useful ones. So, Always go for an RO water purifier that comes with a TDS Controller or Mineralizer that retains the natural Minerals in the water.

Types of Reverse Osmosis Water Purifiers

In India, they are two kinds of RO purifiers available for the Home Purposes.

  • Undersink RO Purifier
  • Wall Mounted Ro Purifier

Both the Undersink and Wall Mounted RO Purifiers have a Storage Tank that stores the Purified Water. Even though there is a Power Outage, the water stored in the tank will be available for use.

Wall Mounted RO Purifier in India

The Wall Mount RO purifier is the most widely used purifier in India which commonly have a storage capacity of 5-10 liters.

Wall Mounted Reverse Osmosis

The Only Problem with the RO water purifiers is, there is some water wastage. So, you have to use the Dirty water in a proper way; to clean the house and mopping purposes.

Undersink RO Water Purifiers

The Undersink RO Purifiers are gaining a lot of popularity since they can be easily fitted under the Kitchen sink.

Undersink RO Water Purifiers

The Pure Water Outlet Tap is fixed next to your Kitchen Tap and will be very easy to operate.

These type of Ro Purifiers are fitted with the Air Pressurized RO Water storage containers that have a storage capacity of 5 liters.

These Purifiers are often referred as Under the Counter, Kitchen Sink Water Purifiers.

The Undersink RO Purifiers are acknowledged as the Best Water Purifiers for Home Purpose since the are Kept under your Kitchen Sink and doesn’t occupy much space.

The Pure Water comes from the Tap that will be fitted next to your kitchen sink tap.

As I mentioned earlier, the waste water can be used for Outdoor purposes. You can also use the water for Gardening.

The Undersink Water Purifier is more suited than the Wall Mount Ro Purifier. Since the under sink RO Purifier has a pressurized tank, the pure water comes out with more force.

Advantages of RO Water Purifier

  • The RO Water Purifier Not only kills the Viruses and Bacteria but also removes their Dead Bodies from the water which is not possible in UV water purifiers.
  • Removes the Heavy Metals like Arsenic, Lead and the Dissolved Salts from the Water.
  • RO with TDS Controller/Mineralizer retains natural minerals in the water.
  • Compact and Easy to Maintain, operate.
  • You get safe and tasty drinking water.

Disadvantages of RO Water Purifier

  • Requires High Pressure and the Water is wasted in Reject Stream.
  • If you input 2 liters of Water into RO Purifier, you will get only one liter of
    pure water. (you can use this water for Mopping, Gardening, and Outdoor purposes)
  • Requires Electricity to operate.
  • The Quantity of the Reject Water is the same as the Quantity of Pure Water you get. About 50% of the Water processed through the Ro Water Purifier is Rejected.

The Advantages of the RO Water Purifier Outdoes the Cons of it. The above disadvantages are very minor when compared to the Advantages of RO Water purifier.

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