Difference Between Osmosis and Reverse Osmosis

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Osmosis and reverse osmosis are two methods of water movement through a semipermeable membrane. The semipermeable membrane can be a type of biological or synthetic, polymeric membrane, which allows only certain molecules or ions to pass through it by diffusion.

Let’s understand Osmosis and Reverse Osmosis.

What is Osmosis?

Osmosis is the movement of water molecules through a potential gradient. It occurs through a semipermeable membrane, which is mainly the plasma membrane of the cell. Water molecules move from a higher to a lower water potential until the water potential of either side of the semipermeable membrane becomes equal. The two main types of osmosis that can occur in the cell are endosmosis and exosmosis.

  • Endosmosis occurs when cells are placed in a hypotonic solution, which has a higher water potential when compared to the cytosol. Sometimes, the cells can burst open due to the filling with too much water.
  • Exosmosis occurs when cells are placed in a hypertonic solution, which has a lower water potential when compared to the cytosol. Cells become shrunk with the loss of water.

Applications of Osmosis

Following are some of the applications of Osmosis:

  • The opening of the stomata, which involves the gas exchange in plants
  • Absorption of water from the soil by roots
  • The effect on freshwater and saltwater fish when they are put into water with different salt concentrations
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What is Reverse Osmosis?

Reverse osmosis (RO) is the opposite of osmosis, which occurs against the water potential. It is done by increasing the pressure of the concentrated side or the side with the lower water potential. This will keep most of the salts in the concentrated side while moving water molecules to the side with the high water potential. Hence, the applied pressure overcomes the osmotic pressure of the system.

Applications of Reverse Osmosis

Following are some of the applications of Reverse Osmosis:

  • Water purification systems that produce desalinated water use water from natural sources, which carry contaminants. These contaminants do not pass through the RO membrane, which is semipermeable. Hence, demineralized, desalinated or deionized water can be obtained through reverse osmosis. This process is also known as ultrafiltration.
  • Bacteria in the intestine that cause cholera make the intestine unable to absorb water. This is done by reversing the normal flow of osmosis. It may cause severe dehydration and sometimes death.

Similarities Between Osmosis and Reverse Osmosis

Following are the similarities between Osmosis and Reverse Osmosis:

  • Osmosis and reverse osmosis occur via a semipermeable membrane.
  • In both processes, mainly water molecules move across the membrane.
  • Both process do not allow solute particles to cross the membrane.
  • Furthermore, the osmotic pressure affects both processes.

Difference Between Osmosis and Reverse Osmosis

Both osmosis and reverse osmosis are phenomena that refer to the movements of water molecules across a semipermeable membrane, still, there are some differences between the two.

Osmosis and Reverse Osmosis
ParameterOsmosisReverse Osmosis
DefinitionA type of diffusion where the movement of water molecules occurs from a high water potential area to a low water potential area across a semipermeable membrane.A process where water is passed across a semipermeable membrane against the concentration gradient facilitated by high pressure.
Energy RequirementOccurs without an energy requirement.Needs energy to supply pressure.
DirectionOccurs from high water concentration to low water concentration.The direction is opposite to that of osmosis, i.e., occurs against the concentration gradient.
Occurrence Naturally occurring. Externally applied.
Osmotic PressureNaturally occurring osmotic pressure works during osmosis.A pressure greater than the naturally occurring pressure is applied.
ApplicationsPlant roots absorb water from the soil, water moves in and out from all cells and our kidneys absorb water from our blood.Used in water filters, refrigeration, water purifiers, brewing of beers, in hospitals for sterilization, and in chemical analysis.
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How Does RO Water Purifier Work?

Public water suppliers work hard to provide clean water for their customers. The problem is that there are many contaminants, especially those that cause taste and odor issues, which are simply not EPA-regulated. These contaminants can easily penetrate aquifers, streams, and rivers, bringing impurities straight to your water lines.

That’s where Reverse Osmosis comes in. With a Reverse Osmosis filtration system, you can filter out impurities and produce outstanding drinking water for your home or business.

Reverse Osmosis (RO) is a water treatment process that removes contaminants from water by using pressure to force water molecules through a semipermeable membrane. During this process, the contaminants are filtered out and flushed away, leaving clean, delicious drinking water. Reverse osmosis is capable of removing up to 99 percent of 65 different contaminants, including lead, fluoride, chlorine, dissolved salts, and more.

There Are Generally Four Stages In The Reverse Osmosis Process:

  • Sediment Filter: This pre-filter stage is designed to strain out sediment, silt, and dirt and is especially important as the sediment filter protects dirt from getting to the delicate RO membranes that can be damaged by sediment.
  • Carbon Filter: The carbon filter is designed to remove chlorine and other contaminants that affect the performance and life of the RO membrane as well as improve the taste and odor of your water.
  • Reverse Osmosis Membrane: The semipermeable RO membrane in your RO system is designed to allow water through, but filter out almost all additional contaminants.
  • Polishing Filter: In a four-stage RO System, a final post filter (carbon filter) will “polish” off the water to remove any remaining taste and odor in the water. This final filter ensures you’ll have outstanding drinking water.

Pros and Cons of Reverse Osmosis

The following are the pros and cons of the reverse osmosis process.

  • Unlike other forms of water filtration, reverse osmosis is considered one of the most all-around effective ways of eliminating water contaminants.
  • For communities for which the only other option for drinking water comes from disposable plastic bottles, reverse osmosis may be a safer and more environmentally friendly option.
  • Water filtered with reverse osmosis makes cooking taste better since it lacks the presence of minerals, including municipally-added fluoride.
  • Wastes significantly more water than it produces.
  • Removes some of the healthy minerals present in water and decreases pH.
  • Costly installation and requires expensive maintenance.


What are osmosis and reverse osmosis?

Osmosis is a process in which liquid water flows through a semipermeable membrane from a diluted solution into a more concentrated solution. The process of movement of a solvent through a semipermeable membrane from the solution to the pure solvent by applying excess pressure on the solution side is called reverse osmosis.

What is the principle of reverse osmosis?

Reverse osmosis ( RO) is a water purification process that removes ions, unwanted molecules, and larger particles from drinking water using a partially permeable membrane. As a result, the solute is kept on the membrane’s pressurized side and the pure solvent is allowed to pass to the other side.


Osmosis and reverse osmosis are two methods of water movement through a semipermeable membrane. The process of movement of a solvent through a semipermeable membrane from the solution to the pure solvent by applying excess pressure on the solution side is called reverse osmosis.

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