Water is essential for life. It needs not to be explained how vital it is. We can feel the problems of contaminated water everywhere. Drinking water may contain numerous impurities, bacteria, chemicals, etc. which are dangerous to health.

A water purifier is necessary to get pure and safe water today. Those were the days when we had to spend an entire day visiting shops one after the other to buy our needs. But today we can buy everything online.

The days are gone when we would spend an entire day visiting shops one after the other to buy our needs.

Reverse Osmosis, Ultraviolet (UV) and Ultrafiltration (UF) are the three most common Water Purifiers used for water treatment.

An RO or a Reverse Osmosis process has been used for decades to purify the water supplies for cities and bottled water.

It is considered the most efficient water filtration method. Reverse Osmosis purifies the water better than other kinds of filters.

What Is Osmosis?

It is defined as a process when the molecules of a less concentrated solution, through a semipermeable membrane, move towards the region of higher concentration of the solution.

For example, when we put raisin in water, the raisin get puffed.

It is a very common example of the process of osmosis in everyday life.

What Is Reverse Osmosis?

Reverse Osmosis is opposite to Osmosis. It is done by applying pressure in a direction opposite to the osmotic pressure.

It is a method of water purification, in which pressure is applied to force the water through a filter.

It is a special type of filter that removes the salts of calcium, magnesium or other impurities from the water. This filter is called a semi-permeable membrane. Large molecules and ions are not allowed to pass through the tiny holes of the membrane.

We get clean water, free of contaminants.

It is a very good method to desalinate sea water.

Industrial wastewater treatment process also involves the use of RO.

Components Of An RO System

The basic components of an RO purifier are:

  • Inlet Valve
  • Sediment Filter and Carbon Block Filters
  • UF Filter
  • Reverse Osmosis Membrane
  • TDS Controller
  • UV Filter
  • Storage Tank
  • Check Valve

Reverse Osmosis Work In Following Steps:

1. Pre-Filtration

Inlet Valve

Water is held on one side of the semipermeable membrane through an inlet valve.

The inlet valve fits into the source of water, i.e. tap water. This water is called feed water.

Sediment Filter and Pre-Activated Carbon Filter

There is a tube which attaches to the sediment filter.

A sediment filter and a carbon block filter removes large sediments and excess of chlorine from water.

UF Filter

UF filter helps in removing bacteria from the water.

This filter protects the RO membrane from the large sediments which may clog its pores.

The excess sediments or chlorine damages the RO membrane the same way they damage other appliances. That is why this pre-filter is used in RO purifiers.

2. The Reverse Osmosis Membrane

In RO purifier, there is a 2 stage arrangement of pressure vessel which contains reverse osmosis membranes.

It is where the real magic of RO system takes place.

The water is forced through this semi-permeable membrane by a high-pressure pump.

The RO membrane is a synthetic plastic material with very tiny pores. It works as a filter which allows the passage of water molecules but prevents the large particles (like urea, bacteria, viruses or dissolved salts) to pass through it.

TDS Controller

A good purifier has an in-built TDS controller.

A TDS controller balances the TDS Level of Water.

It ensures that the TDS of water is neither very high nor too low.

Drinking water with high or low TDS acts like a poison and affects the health.

The heavy metals present in as the dissolved solids in water may cause Cancer and Nerve damage.

TDS present in water affects children more than the adults.

Studies Reveal That Reverse Osmosis Drinking Water Purifiers Are Capable of Reducing:

  • Copper
  • Lead
  • Fluoride
  • Barium
  • Nitrates and Nitrites
  • Cyst
  • Arsenic
  • TDS (Total Dissolved Solids)
  • Traces of Benzene
  • Bad Odours and Bad Tastes
  • Heavy-Metals (for example, Cadmium)

3. Post Filtration

UV Filter

There is a UV filter which removes the remaining contaminants in water. This water then fills up the storage tank until we use it.

Post Carbon Filters

Finally, there is an activated carbon filter which gives a final polish to the water before it comes out of the tap.

It is used to remove any odours or flavours that may come from the hosepipes or the water holding tank.

4. Check Valve

The check valve ensures that the water does not flow backwards from the storage tank.

There is an automatic shut-off valve which turns an Reverse Osmosis purifier on and off according to the water level in the storage tank.

Frequently Asked Questions

1. What are the Types of Membranes Used in Water Purification Process?

UF Membrane

The salt concentration in river water is low. We need to remove only the germs and dirt present in water. UF is an ideal membrane for such kind of water. It requires low energy consumption.

RO Membrane

When there is a high salt concentration in water (for example, sea water, brackish groundwater, etc.), reverse osmosis membranes are the best.

The membrane surface has very small pores.

Only water and the molecules smaller than the water molecules can pass through the membrane surface.

This treatment process delivers potable water, free of chemicals.

2. How Do Reverse Osmosis Systems Purify Water?

A water purifier purifies water in three steps:

  • Removal of visible and dissolved impurities.
  • Deactivation of bacteria and viruses.
  • Reduction of dissolved contaminants.

Reverse Osmosis works on the principle of cross-filtration.

It uses two outlets. One outlet is for pure water, and the other is for discharging the impure water or reject water.

This process uses a high pressure pump to increase the pressure on that side, where water has a high salt concentration.

The pressure pump works as a driving force which pushes the water to pass through the semi-permeable membrane. It leaves 99% of the high salt content in the reject stream.

A high concentration of dissolved salts in the feed water means high pressure is required to overcome the osmotic pressure.

3. What are the Types of RO Purifiers?

Undersink RO Purifier

Nowadays, this type of purifiers is gaining wide popularity.

They can be fitted under the sink of the kitchen and does not occupy space.

The outlet tap of the purifier is fixed close to the kitchen tap. It makes it easy to operate the purifier.

It has a storage capacity of 5 litres.

Wall Mounted RO Purifier

This type of purifier is widely used in India.

It has a storage capacity of 5-10 litres.

The only con of using this type of purifier is the wastage of water.

4. What are the Pros of Reverse Osmosis Water Purifiers?

Reverse Osmosis filter is the best cartridge filter due to the following reasons:

We get pure and fresh drinking water from RO purifiers.

It removes heavy metals and dissolved salts from water. It is an ideal treatment for brackish water. The removal of dissolved salts brings the pH in drinking water to a normal level.

RO purifier kills bacteria and other micro-organisms. It also removes their dead bodies from the water.

It is easy to use and maintain.

A good RO purifier can eliminate 99% of the TDS from the water.

RO purifiers with a TDS controller retains essential minerals in the water.

Reverse Osmosis purifier uses a process known as cross flow. This process allows the membrane to clean itself.

RO uses membrane technology to provide fresh water, which works without any addition of harmful chemicals.

5. What are the Cons of Reverse Osmosis Water Purifiers?

One of the major disadvantages of using an RO purifier is the wastage of water. Around 50% of the total water we input, get wasted in the reject stream. However, you can use this water for washing your vehicles, gardening, mopping, etc.

It requires a lot of water to induce the pressure needed for filtration. For example, if you input 2 litres of water, you will get only 1 litre of pure drinkable water.

It requires electricity to operate.

Though there are some cons of using an RO purifier, those cons are minor when compared to the pros of using it.

In fact, the pros of using an RO purifier overlook its cons.

6. Other Methods of Water Treatment

There are various methods of water purification.

Apart from the water purifiers used for water treatment, an Ion exchange water softener is also a well-known method for quite a long time. It is used to remove the hardness of water. It replaces the salts of calcium and magnesium (like calcium carbonate, magnesium sulphate, etc.) with the salts of potassium.

This method is widely used for treating industrial water. It has also been used for municipal wastewater treatment.

However, it does not remove fluorine from the water!


A good water purifier removes the contaminants and retains the minerals in the water. It not only satiates the thirst but also gives a satisfaction of drinking healthy water.
If you also have water quality issues then, RO drinking water purifier with a TDS controller must be considered.
Don’t rush to buy a cheap and unbranded water purifier without a TDS controller. It destroys the useful minerals from water along with the impurities.