What is the Difference Between Osmosis and Reverse Osmosis?

The main difference between osmosis and reverse osmosis is that Osmosis is the natural movement of water molecules through a semipermeable membrane from a region of lower to higher concentration, whereas, Reverse Osmosis occurs when pressure is applied to reverse the flow of water molecules to separate liquids from solids by applying a pressure differential across the membrane.


What is Osmosis (Forward Osmosis)?

Osmosis is the natural process of diffusion of water molecules through a semi-permeable membrane from a region of lower to higher concentration. This happens because there is an electrochemical potential difference across the membrane, which creates a concentration gradient.

The concentration gradient causes water molecules to diffuse into the region with the higher concentration and exit from the region with the lower concentration.

What is Reverse Osmosis?

Reverse Osmosis is a process of water purification that allows molecules of different molecular weight to pass through the membrane while only the molecules that can pass through the membrane will remain. Reverse osmosis is used to remove dissolved substances, such as salt and minerals, from seawater or other sources. In reverse osmosis, water moves across a semipermeable membrane by forced convection.

The most common forms of reverse osmosis are batch processes and continuous processes. Batch processes use membranes with a small pore size to separate out smaller substances in water while continuous processes use membranes with large pores that allow larger substances to pass through more easily.

What is the Difference Between Osmosis and Reverse Osmosis?

Osmosis is the natural movement of water molecules through a semi-permeable membrane from a region of higher to lower concentrations. Reverse osmosis occurs when pressure is applied to reverse the flow of water molecules across a semipermeable membrane, which separates liquids from solids by applying pressure differential across the membrane.

Reverse Osmosis vs. Osmosis

Reverse osmosis and osmosis are two different processes that react to the same principle of natural movement of molecules. They are two different ways of removing dissolved solids in water.

The difference between these two methods is how the pressure differential is achieved. In reverse osmosis, a high pressure differential is applied across the membrane to force the molecules through the membrane against their respective concentration gradients.

In Osmosis, there is negligible pressure difference across the membrane and hence, no force exerted to move molecules through it, they naturally flow from regions of lower concentration to regions of higher concentration without any effort on behalf of the individuals.

Reverse Osmosis

Reverse osmosis is a process that uses pressure to force water through a membrane in order to purify it of dissolved salts and other contaminants.

In reverse osmosis, a semi-permeable membrane separates two solutions of different concentrations. The solution with the higher concentration (the feed side) contains dissolved solids that are to be removed from the solution on the other side (the permeate side). Pressure is applied across the membrane from the feed side to the permeate side, causing water molecules to pass through the membrane and leave behind any dissolved solids. The result is a solution with lower concentration of dissolved solids than before processing. This process can be used for desalination or for pre-treatment of wastewater before it is further treated by other methods.

Image Source: CSUN

The process of reverse osmosis can be divided into three stages: pre-treatment, pressure application and post-treatment. The pre-treatment stage includes steps to remove particles that could potentially clog the membrane and to ensure that the pressure applied across the membrane is effective in separating water from solids. Post-treatment involves steps to remove any residual salts or other contaminants from the water after it has passed through the membrane.

Reverse osmosis is used in a variety of applications, such as desalination of seawater and brackish water, pretreatment for laundry detergents and removal of dissolved solids from industrial waste streams. It is also used in the pharmaceutical industry to remove dissolved solids from solutions of drugs, vitamins and other chemicals.


On the other hand, Osmosis is the process of diffusion through a semi-permeable membrane. It is a different process from reverse osmosis, which relies on pressure to drive water across a membrane. Osmosis is the diffusion of water across a semi-permeable membrane, driven by the solvent potential.

Osmosis is an important process in biology and also occurs in some materials, such as partially dehydrated potatoes. Osmosis can be used to separate salts from water or to concentrate solutes from solutions by drawing them through a semi-permeable membrane. The process of osmosis can be used to desalinate water or to provide fresh water in arid areas and has potential applications for purifying industrial wastewater and treating sewage.

Forward Osmosis vs. Reverse Osmosis
Image Source: CSUN

Osmosis is a physical process that occurs due to the movement of solvent (water) through a partially permeable membrane, separating two solutions of different concentrations. The driving force for this movement is known as osmotic pressure. If the membrane is semi-permeable and only small molecules can pass through it, then osmosis will result in the diffusion of water across the membrane, from an area of low concentration to high concentration until an equilibrium between both sides is reached. The process will stop when this equilibrium has been reached.

The word osmosis can also be used to describe a physical process in which a solvent travels through a partially permeable membrane (as in the definition above), but with no solvent on the other side. In this case, the solvent is known as a pure substance.

The process of osmosis is used in many areas of science, including biology, chemistry and physics. For example, osmosis plays an important role in the function of kidneys and cells. In the human body, osmosis is also responsible for maintaining the balance of fluids and salts between cells and the blood. The process can also be used to remove impurities from liquids or to separate certain substances from a mixture.

Similarities Between Osmosis and Reverse Osmosis

The two processes are similar in that both act as a means of separating substances based on their concentration. There are differences between the two, but they are still closely related.

Reverse osmosis is often used to remove salt or minerals from a solution by applying pressure across the membrane and creating a difference in pressure. Osmosis is most commonly used to clean water.

The end result of both methods is the separation of particles based on their concentration, but reverse osmosis also requires a large amount of energy input to create pressure while osmosis does not.

Advantages of Forward Osmosis

The main advantage of Forward Osmosis is that it uses virtually no energy.

Going back to the terms, Reverse Osmosis is when water molecules are pushed from a region of higher-concentration to a region of lower concentration. This process needs quite a bit more pressure, and more work than Forward Osmosis. With Forward Osmosis, there’s less pressure needed and less work to be done.

This means that there’s less energy used in the process as well. The downside is that Forward Osmosis doesn’t filter out any particulates or salts from the source water at all (unless you’re using a membrane with a low permeability).

Advantages of Reverse Osmosis

Reverse osmosis has a number of advantages. It is a more efficient method for water purification and can be used to produce drinking water, desalination, or other purified products.

Additionally, it offers flexibility in the scale of the equipment needed to produce the desired product. Reverse osmosis membranes can be scaled from small, portable units to large production facilities that can provide large quantities of water at greater efficiencies than any other method of water purification.

Additionally, it has the potential for low capital investment and low operating costs because these pumps are commercially available and require little maintenance. Finally, reverse osmosis is an environmentally friendly process because it does not create waste byproducts such as chemical waste and contaminated sediments like some other types of treatment do.

Difference between Reverse Osmosis and Osmosis


Osmosis and Reverse Osmosis are similar in that they both remove solutes from water, but there are some key differences. Reverse Osmosis is used to remove large molecules and ions from water, while osmosis is used to remove smaller molecules. Reverse Osmosis also removes more solutes than osmosis.

The two methods also use different equipment and techniques. Reverse Osmosis typically uses a membrane to filter larger molecules while osmosis usually uses a semi-permeable membrane.

Meet the author: Paul White

Paul is water engineer by trade and is very passionate about innovative solutions for water filtration. His goal is to make drinking water accessible and affordable to all. An avid runner, he is currently training for a marathon. “Running is my sanity. Writing is how I organize my thoughts. I’m a poet and writer who is passionate about change. I aspire to be the best version of myself, and to help others do the same.” Learn more about Paul and the rest of the team.