Lots of people wonder, “what is reverse osmosis?” Well let’s break down what you should know about this vital water system

updated: February 28, 2020
RO filter and a glass of water.
RO filters are the most advanced filters available today.

Lots of people wonder, “what is reverse osmosis?” Well let’s break down what you should know about this vital water system

One topic a ton of homeowners struggle with is understanding why reverse osmosis (RO) is important. The truth is, this often-overlooked filtration system plays an integral role in the water quality.

What is RO

No matter where you live, the purity of you and your families water is extremely critical. That said your local water-treatment process may not be quite enough on its own. The primary job of any municipal treatment facility is ensuring the safety of water by adequately removing any living bacteria.

Installed RO filter.

As such, it’s often up to you to improve the flavor and overall quality of your family’s water. There are other options, but a very tried and tested option is known as reverse osmosis. People have been aware of this for over 100 years now, with easily purchased home-units available since the 60s.

Reverse osmosis (RO) removes the vast majority of potentially dangerous substances found in drinking water, upwards of 98%. The house’s feed water is sent through a specialized set of filters at intense pressure. As opposed to regular osmosis, a passive process seeking to achieve equilibrium on two sides, RO takes force, which prevents equilibrium.

As this technology has become the norm, businesses have greatly expanded the capability of this process. So much so, by simply opting for some key post-treatment processes, reverse osmosis can produce water suitable for nearly any application.

Why Use RO Filtration

Reverse Osmosis is some of the most comprehensive filtration systems available. However, they’re also relatively cost-effective. They’re a viable option for the average homeowner concerned about the purity of their water. A less efficient option for individuals looking to lower dissolved material in their kitchen line is a generic water distiller. However, there are other ways to improve water quality, that every homeowner needs to be aware of.

Sediment in kettle.

As mentioned, most RO systems can boast the removal of about 98% of all dissolved material found in feed water. Doing so significantly decreases the chances of any adverse health impacts from ingesting the water regularly. However, other important reasons to finally purchase a RO system include:

  • Eliminate bad taste or smell of water
  • Greatly reduce any potentially harmful dissolved substances
  • More environmentally friendly than bottled water
  • Easy to install, even easier to use
  • Most types fit right under the faucet

How The RO Process Goes Down

Reverse osmosis systems are best described as multi-staged filtration systems. For the most part, the number of stages will have the most significant impact on what a given system can accomplish, and how efficiently.

The most crucial part of any reverse osmosis system is the semipermeable membrane itself. These membranes are made from spirals of material, covered in holes that are generally only 1/100th the diameter of a human hair. Originally these membranes were produced from cellulose acetate, but now they’re usually constructed from an advanced thin film composite.

How reverse osmosis works.

Before water reaches the RO membrane, it passes through some prefiltration. The number and efficiency of these prefilters will depend on the quality of your system. They generally contain a mixture of carbon filters, which improves the taste by removing substances such as Hydrogen Sulfide, and water sediment filters, which eliminates large, undissolved silt.

After finishing prefiltration, the water is pressed through the specialized RO membrane. It’s then separated into two lines, permeate and brine. The newly cleaned water, called permeate, is fed into a storage tank. As such, the size of your tank is critical. It takes the average system a couple of minutes to produce a single glass of water. So make sure to get one suited for your specific needs.

Meanwhile, the leftover contaminated water, called brine, is generally sent to the house drainage. Many modern RO systems also include a postfiltration step to finish off your water right before it hits the faucet.

Clean water is drawn out of your storage tank and undergoes this final step. Reverse osmosis systems will last for a very long time if they’re properly maintained. This means replacing prefilters every year and replacing the main membrane every 2-4 years.

Frequently Asked Questions About RO

Lots of people have questions revolving around reverse osmosis. Some of the most consistent questions involve where they make the most sense to use.

RO filter concept.

As discussed, most systems are designed to be used at the point of use, such as under the sink. This is especially true for anyone who gets their water directly from a well. Another common application of RO filtration is ensuring the perfect chemical composition of aquariums.

While useful in many situations, reverse osmosis filtration is not ideal for everything. For instance, it’s not typically used for an entire house. The tank would need to be massive to provide adequate water for showers, laundry, and toilets. Not to mention how none of these things require RO filtered water in the first place.

Other people often ask if RO is wasting water. Bottom line is, there is always a bit of water left over. However, the amount which is sent back down the drain is greatly impacted by the type of system you have.

RO filtration system.

Some types of RO system aren’t designed to be efficient. They only typically produce a half gallon of clean water for every two gallons sent down the drain. However, these days many are made to be used with a permeate pump. This simple addition reduces wastewater by around 80% by storing the brine in the pump, which reduces pressure on the RO membrane itself.


Have you ever used a reverse osmosis system in your house? Do you think extra prefiltration is necessary in most cases? Do you think it’s important to minimize the wastewater by installing a permeate pump? Please leave us a comment below and let us know!

Daniel Pleasants is an expert on all things about home appliances. He is currently a dealer and installer of whole house water filtration systems and water softeners in the Seattle, Washington area.
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