How Does Reverse Osmosis Work?

How reverse osmosis works


Reverse osmosis is a powerful filtration method that can pull a lot of harmful gunk from your water. But how does it actually work?

With homeowners becoming increasingly aware of health issues caused by water contamination, interest in home water filtration is growing. One powerful filtration method that is gaining popularity is reverse osmosis. Before choosing this filtration method, consumers should educate themselves about how it works, its benefits and its disadvantages.

What Is Reverse Osmosis?

As you probably remember from science class, osmosis is the diffusion of water through a cell membrane. It works because cell membranes are semi permeable. This means that they allow water to pass through easily but restrict the passage of other substances. When only water can pass through a membrane, the solutions on either side of the membrane tend toward equilibrium. This means that water flows from the more dilute solution to the more concentrated one until the concentrations on either side of the membrane are roughly equivalent.

To effectively filter water, you need to separate pure water from the contaminants dissolved in it. Osmosis is not a good method of doing this because it produces two solutions of roughly equal concentrations instead of one solution that is concentrated with contaminants and another that is very dilute. Reverse osmosis, on the other hand, is a good filtration method because it produces two solutions of unequal concentrations.

Like osmosis, reverse osmosis involves the passage of water through a semi-permeable membrane, but in reverse osmosis, the water travels away from the more concentrated solution rather than toward it. Outside force drives the water through the membrane toward the more dilute solution, and the membrane prevents most contaminants from passing through it. Because the more concentrated solution is full of contaminants, this process produces clean water.

How Does a Reverse Osmosis Filtration System Work?

Using a durable semi-permeable membrane, a typical reverse osmosis system removes water from dissolved contaminants. The clean water goes into a holding tank for future use, and the water containing the dissolved solids goes down the drain.

What Are the Pros and Cons of a Reverse Osmosis Filtration System?


​Unlike mechanical filtration, reverse osmosis effectively removes dissolved solids from tap water. In fact, reverse osmosis removes approximately 95 to 99% of total dissolved solids from water. The process removes salt, nitrates, heavy metals, dissolved minerals, some microorganisms, certain pesticides and other substances that produce unpleasant tastes and odours. This results in clear water that tastes pure.

In addition to producing clean, palatable water, reverse osmosis is useful for filtering water used in aquariums, machinery and various industrial processes. By removing dissolved solids, reverse osmosis produces water that is less likely to corrode or otherwise damage mechanical components than mechanically filtered water. This reduces operating costs and helps prevent downtime caused by breakage.


Reverse osmosis systems are extremely effective, but they require upkeep. They use membranes that can be damaged by chlorine, other additives and contaminants. Protecting membranes from these substances requires the use of pre filters. Most systems use both sediment and carbon pre filters for this purpose.

Filter upkeep is a small price to pay for the high level of effectiveness they provide.

Who Should Consider a Reverse Osmosis System?

A large variety of commercial enterprises, including food service establishments, can benefit from using reverse osmosis for water filtration. In addition, certain residential customers should consider these systems. Homeowners who should think about using this type of water filtration include those with softened well water and those who have water with taste or appearance problems that cannot be solved through the use of standard carbon filters.