What Is Reverse Osmosis Filtration?

What Is Reverse Osmosis Filtration?

If you’re worried about the rise in water safety crises, widespread chemicals known as PFAS in your water supply and the negative effects of bottled water on our planet, you’re not alone. 

You’ve probably started to investigate a water filtration system. You may have even come to the conclusion that reverse osmosis filtration is one of the best methods for comprehensive water purification.  

But if the last time you heard the word “osmosis” (let alone “reverse osmosis”) was grade school biology – and you weren’t sure what it meant then and you’re still not sure now – we’ve got you!  

Here, we break down what reverse osmosis (RO) is, how RO filtration systems work and why RO filtration will benefit your home and office (but without setting you any science homework – you’re welcome). 


What is reverse osmosis water filtration?

In a nutshell, RO filtration forces water through a membrane that traps contaminants, allowing fresh, pure water through.  

Here’s the science bit. Osmosis is the movement of water molecules from a stronger solution with a high concentration of water molecules to a weaker solution with a lower concentration of water molecules, through a cell’s partially permeable membrane. 

Reverse osmosis (RO) uses the same fundamental process. It applies enough pressure to move water molecules out of the stronger solution (the contaminated water), into the weaker solution (the pure water).

RO overcomes this natural “osmotic pressure” to force unpurified water through a semipermeable membrane perforated with 0.0001-micron pores. Microscopically small, virtually the only things that can slip through these pores are water molecules.


Why is reverse osmosis so effective?

Chemical or carbon filtration systems use certain materials to attract or directly target the contaminants, but they cannot remove bacteria, viruses or dissolved solids from water.  

RO is more effective. By pushing water through a microscopically small filter material, it removes total dissolved solids (TDS) from water. Examples of TDS include salts, “forever chemicals” known as perfluoroalkyl and polyfluoroalkyl substances (PFAS), nitrates, fluoride and heavy metals such as lead and arsenic. 

Neither ultrafiltration (0.1 to 0.01 micron pores) nor nanofiltration (0.001 micron pores) can achieve that level of contaminant reduction.


How does reverse osmosis water filtration work?

man holding a glass with water being splashed in

Originally developed to desalinate sea water, RO filtration has become a popular water purification system for homes and offices. Available in both undersink filtration systems and water dispensers, the RO filtration process works the same in each one. Here’s what happens.


1 Sediment removal 

Incoming (or feed) water first passes through the sediment stage, where solid particles are removed. 


2 Carbon prefiltration 

Water then passes through a pre-carbon or granular activated carbon (GAC) filter, where it undergoes prefiltration to remove chlorine. The removal of chlorine at this stage is crucial because it can damage the RO membrane in stage three.


3 RO filtration 

The water enters the RO cartridge where the RO membrane is housed. Water pressure forces the prefiltered feedwater into the RO filter, blocking contaminants. 

Up to 99.97% of contaminants are blocked during RO filtration. These rejected contaminants form a brine that’s automatically and regularly flushed out of the system and into a wastewater tube that’s connected to an external drainpipe.


4 Post-filtration 

The purified water undergoes the final filtration stage, via a GAC or carbon block. This post-carbon stage removes any residual impurities. A remineralization cartridge could be added here to alkalise the purified water.


5 Enjoy! 

Pure, fresh water finally travels to a cooler or dedicated faucet for you to enjoy at your convenience.


How does the reverse osmosis membrane work?

The RO membrane is the key filter in a RO filtration system or dispenser. Here we break down the structure of the membrane to show how it works.

  • The membrane element is composed of multiple spiral-wound layers. 
  • Each layer consists of two RO membranes that sandwich a porous sheet called a permeate carrier. 
  • This “sandwich” is glued together on three sides to form an envelope. 
  • The open end of this envelope is attached to the center permeate tube, which is perforated with tiny holes into which the purified water is channeled.
  • After all the envelopes are attached, a mesh feedwater spacer is placed between each one. 
  • The assembled layers are then wound around the purified water tube to form the membrane element, which is inserted into its cartridge or housing. 
  • The addition of the mesh spacers will ensure the feedwater is evenly distributed throughout the membrane element.


What is the pH of reverse osmosis water?

RO is so effective that it not only removes the big stuff, like sediment, toxins, microbes and lead, but also substances that have actually dissolved in the water. So microscopic are the pores in the RO membrane that even minerals usually present in water are removed. 

This lowers the pH of the water, making it slightly acidic. After treatment, RO water has an average pH of between 5 and 7. This pH level is considered healthy for human consumption. 


What are the benefits of reverse osmosis water?

Environmental Working Group (EWG), a public health advocacy organization that has called for more regulation of PFAS, says the gold standard for in-house filtration is an RO filter. There are other environmental and lifestyle benefits, too.


Peace of mind

RO filtration is an ideal way to rest in the knowledge that your water is always safe. PFAS can slip through many filters, but researchers at Duke and North Carolina State universities found RO and two-stage filters are the most effective

With 0.0001-micron pores, an RO membrane can remove a broad swath of dangerous contaminants, such PFAS. So when you install an RO filtration system or dispenser, you ensure fresh, clean water is easily accessible.



Because an RO filtration system works with your home or office’s own water system and typically comes with a dedicated faucet, purified water is always available. It empowers everyone in your home or office to make healthier hydration choices. 

And don’t forget pets and plants! They prefer and need fresh, clean water that’s free of human contaminants and rich in healthy minerals like calcium and magnesium, too.


Tastes great

close up of a woman's hand holding a glass of water


Water that’s had the chlorine removed from it tastes far more pleasant, so it goes without saying that foods cooked with or in RO-filtered water will be more palatable, too. RO-filtered water also makes for healthier cooking. All contaminants, such as asbestos, have been removed, so using it in your cooking means safer food.

RO-purified water is therefore ideal for preparing baby formula, tea, coffee and cocoa, as well as cooking hot cereals, soups, rice and pasta. 



With an RO filtration system, there’s no need to sign up for an expensive bottle delivery service and no worries about water bottles running low.


Kind to the environment

Kick the single-use plastics habit to the curb for good. Not only do repeated purchases of water bottles add up over time, the negative impact of these bottles on health and the environment is catastrophic. An in-home or in-office RO system makes it incredibly easy to switch to reusable sports bottles and glasses. 


At Brio you’ll discover a wide selection of high-quality reverse osmosis systems and dispensers that provide solutions to your drinking water concerns. We use only premium materials and components, and our reverse osmosis membranes are certified NSF/ANSI 58, which is the industry gold standard for the removal of TDS.



Back to blog

Leave a comment

Please note, comments must be approved before they are published