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What is Reverse Osmosis?

You’ve probably heard of the reverse osmosis (RO) process, and most likely have drunk water, taken medicine, or eaten food whose production includes reverse osmosis. Even though you have most likely heard of it, you may have also wondered “what is reverse osmosis?”

Although the term can seem daunting, at its core, reverse osmosis is a process for filtering substances. Usually, those substances are water, but they can be other liquids or even gasses. 

Gaining a better understanding of what reverse osmosis is and how it works can help you decide on the appropriate water treatment option for your needs. At the end of this, you might find yourself on the hunt for a reverse osmosis filtration system.

Reverse Osmosis Systems starting at only $25/mo. Try before you buy!

What is Osmosis?

To understand how reverse osmosis works, you must first get a better idea of what the process of osmosis is. Osmosis is a natural process that occurs in our bodies and in the world around us. It is how your cells take in nutrients and water, and how plants receive nutrients and moisture from the soil they are planted in.

Osmosis occurs when a solvent moves across a semipermeable membrane from a solution with a low concentration of solutes to a solution with a high concentration of solutes. 

Let’s break down what these terms mean:

  • Semipermeable membrane – This is any membrane that allows some molecules through but not others.
  • Solvent – This is any fluid that passes through the membrane.
  • Solute – This is a dissolved substance in the fluid.
  • Solution – This is both the solute and solvent combined. The solution exists on both sides of the membrane.

The term osmotic pressure is used to describe this tendency for a fluid to move across a membrane to a solution that has a higher concentration of solutes.

How is Reverse Osmosis Different?

Reverse osmosis doesn’t occur naturally. Instead, reverse osmosis requires the application of force, in the form of hydrostatic pressure, to a solution with a high concentration of solutes. This solution is then forced through a specially designed membrane that blocks molecules larger than water. The result on the other side is a solution with a low concentration of solutes.

How is Reverse Osmosis Used?

The practical application for reverse osmosis systems is to reduce the number of dissolved solids, or solutes in a solution. 

Most often the solution used in a reverse osmosis system is water. Water is forced through a membrane that has pores large enough for water molecules to pass through, but too small for the minerals, metals, bacteria, viruses, and other contaminants that water often contains. This helps answer the question, “what is reverse osmosis water?”.

Reverse osmosis was first invented in 1748 by a French physicist and clergyman, but it spent nearly 200 years confined to laboratories. It wasn’t until the University of California Los Angeles opened the first desalination plant in 1950 that reverse osmosis entered the public sphere.

Here are some of the most common uses of reverse osmosis:

  • Agriculture – Reverse osmosis water is used in agriculture to remove carbonates from water, allowing for more effective nutrient delivery to plants.
  • Power Plants – Power plants use RO water in the boiler for steam generation, improving efficiency and reducing maintenance costs.
  • Pharmaceuticals – Medicines are manufactured using RO water due to purity requirements.
  • Winemaking – Winemakers use reverse osmosis to reduce the amount of alcohol in the wine.
  • Food Manufacturing – Reverse osmosis is used to manufacture fruit juice concentrate and to extract whey protein isolate from cheese.

There are many other applications that reverse osmosis is used for, not the least of which is for removing contaminants from residential potable water. Residential RO systems are a cost-effective and highly efficient alternative to purchasing bottled water or utilizing a bottled water delivery service.

Here are some of the core advantages of using RO systems in a residential setting:

  • Saves space – RO systems require less room than other filtration methods, making them ideal for installation under sinks.
  • More efficient – Reverse osmosis systems are more efficient than many other comparable filtration systems.
  • Effective – Residential RO systems can often filter remove 95% or more of total dissolved solids from a sample of water.

If you have ever asked, “what is RO water?”, the short answer is water that contains very little contaminants. With a residential reverse osmosis system, filtered water is delivered straight from the tap water source at your kitchen sink. The benefits of reverse osmosis water are right at your fingertips.

Closing Thoughts

Reverse osmosis is an incredibly important process in today’s world. It is used to manufacture the medicine we use, the food we eat, and most importantly to filter the water we drink. 

Reverse osmosis is a process that can remove impurities and unwanted contaminants. In a reverse osmosis system, water is forced through a specially designed membrane that allows water molecules through but doesn’t allow other contaminants. The result is potable water without many of the carbonates, metals, and other substances that it normally carries.

To learn more about reverse osmosis systems for residential drinking water, please contact Rayne Water today. We have locations in both Arizona and California! Everything from reverse osmosis systems in Phoenix, commercial to water softeners in San Diego, and whole house water softener system in Ventura! Check out the location nearest you!


  1. Lasky, Jack. 2019. “Reverse Osmosis (RO).” Salem Press Encyclopedia of Science.
  2. Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000. Section 15.8, Osmosis, Water Channels, and the Regulation of Cell Volume. Available from: