What is Reverse Osmosis: The Complete Guide

Want to know what is Reverse Osmosis and if you should consider buying a Reverse Osmosis system? So continue reading our article to find out!

If you are searching for a water filter that provides you great and clean water for an affordable price, you should consider a Reverse Osmosis (RO) water filtration system.

Our experts put together the most accurate information about Reverse Osmosis in an easy-to-digest format to answer all the key questions about the topic.

In this article you will understand what Reverse Osmosis is, how a RO system works, learn about the different parts or stages of a RO system, the advantages and disadvantages of a RO system, if it is good or bad for your health and environment, and much more!

What is Reverse Osmosis

Reverse Osmosis, or RO, is a water filtration process that consists of pushing water through a semi-permeable membrane to remove most of its contaminants.

Not all the water that is pushed to the membrane passes through it, so basically there are 2 streams of water to consider:

  • The permeate, that is the water that successfully passes through the membrane and was filtered of most of the contaminants
  • The concentrate, which is the remaining water that did not pass through the membrane and has a greater concentration of contaminants (and justifying the name of this stream).

Osmosis vs Reverse Osmosis

While Osmosis is a natural process in which the molecules of a less concentrated solution flow through a semi-permeable to a more concentrated one to balance the concentration on both sides of the membrane. An example of osmosis in your day-to-day life is when your kidneys absorb water from your blood.

Reverse Osmosis, as the name suggests, is the reverse of it. But because it is not a natural process, some energy input is required, putting pressure on the more concentrated solution to push it through the membrane. So, instead of creating a balance between the solvent and solute in both solutions, we are separating the solvent (water) from the solute (contaminants).

How does Reverse Osmosis work?

Reverse Osmosis works by putting pressure on the unfiltered water to make it pass through the semi-permeable membrane, to get filtered water, and leave most of the contaminants (95 to 99%) on the concentrate stream.

This concentrated stream that is left behind with the impurities, can then be filtered again on the RO system or can be flushed through the drain.

The concentrated stream with the contaminants and the permeate (filtered water) do not touch in a Reverse Osmosis system to avoid cross contamination – the permeate goes in a way and the concentrate into another.

Reverse Osmosis removes up to 99% of impurities and several contaminants from your water, as we will discuss in more detail below.

A Reverse Osmosis system typically uses a multi-stage process to get the purest water possible.

Reverse Osmosis Stages

The stages involved in the Reverse Osmosis System are:

Stage 1 – Pre-Filtration:

  • In this stage sediment, dirt, and suspended materials are removed to avoid hitting and clogging the RO membranes.

Stage 2 – Carbon Filtration:

  • In the second stage, a carbon filter is used to remove chlorine before it reaches the RO membrane.
  • This is important because chlorine can damage the membranes, and this stage will extend the life of the RO system, and also improve the taste and quality of your water.

Stage 3 – RO Membrane:

  • The water goes through the RO membrane to filter out several contaminants.

Stage 4 – Carbon Post-Filtration:

  • In the last stage, also known as the polishing stage, carbon post-filtration is used to remove weird taste and odors from the water before you drink it. 

How Much Water Does a Reverse Osmosis System Produce per Day?

Reverse Osmosis systems used at home will generally produce between 10 and 75 gallons (38 to 283 liters) of filtered water per day. This wide range depends on the system you purchase but can give you an overall idea of the capacity interval.

Contaminants removed by Reverse Osmosis

The membranes can filter out contaminants depending on their size (and charge), typically removing particles with a molecular weight superior to 200.

Reverse Osmosis removes several contaminants and impurities that are unhealthy to you, such as heavy metals, organic materials, bacteria, salts, pesticides, nitrates, detergents, fluoride, lead, chlorine, etc.

Removing fluoride from your drinking water can be especially important because many water sources exceed the daily fluoride recommendations that can be harmful to you and your kids, and a RO system removes around 90% of it.

Another contaminant that can be harmful to you that RO is really good at removing is lead. A RO removes up to 98% of lead from the water.

An RO system can also remove up to 80% of chlorine from the water. While chlorine is not harmful in low concentrations, some people like to remove it because of the taste and odor that it gives to water.

How Much of a Contaminant Can a Reverse Osmosis System Remove?

On the graphic below you can check the maximum percentage of each contaminant that can be removed from the water with a Reverse Osmosis System.


Why is Reverse Osmosis a Good Option?

There are very good reasons to consider a Reverse Osmosis System for your house, such as:

#1 – Remove Contaminants from Your Water:

If drinking clean and pure water is important for you, purchasing a RO system is a no-brainer. As covered extensively before, Reverse Osmosis dramatically improves the quality of your water, removing several contaminants and impurities, making it great to drink.

#2 – Better Taste and Odor:

RO not only removes impurities but also improves the taste and odor of the water that you drink. Some contaminants are not harmful if in the lower amounts, but can cause taste issues to your water that RO solves.

#3 – Simple Installation:

There are different RO systems to fit most of the needs, but installing a RO system is simple and easy, and you can have it installed at the kitchen sink, and connected to your refrigerator.

#4 – Easy to Maintain:

RO systems are really easy to clean and replace certain parts if needed, so you shouldn’t be scared by future maintenance.

#5 – Saves Money:

If water quality and flavor are relevant to you, you probably spend money on bottled water. With a RO system, you will have water that is better than bottled water for a fraction of the price, saving you a lot of money.

5 Benefits of a Reverse Osmosis System Infographic

What Are the Disadvantages of a Reverse Osmosis System?

We highlighted some of the benefits of Reverse Osmosis, but it also has some disadvantages:

  • The concentrate stream that is left needs to be discharged, and it can be some environmental impacts that are still being studied.
  • While the maintenance of a RO system is easy, it still requires maintenance. You need to be careful to ensure that the RO membrane is clean and in good condition.
  • For household RO systems, the recovery rate typically is not high, leading to a great amount of water being wasted.
  • Reverse Osmosis removes contaminants, but in the process also removes minerals that might be beneficial to you, like calcium and magnesium. It is important to have a balanced diet to ensure that you consume the right amount of minerals.

Is Reverse Osmosis Bad for Your Health?

Reverse Osmosis is being used on households for decades and there are no indications of harmful health effects. In fact, the US Navy uses distilled water that has even fewer minerals than RO water, and there are no reported health issues.

While RO water does not have important minerals for you like calcium and magnesium, the fact is that water should not be the main source of these minerals for you, as it only has a small fraction of the daily amount needed. So it should not be a problem as long as you have a balanced diet that includes these minerals.

Is Reverse Osmosis Bad for the Environment?

While having wastewater is not ideal, the truth is that if you want to remove contaminants from the water, you should expect that part of it has to be discharged. But it is important to note two important things, not only is the wastewater low, it is not that bad – the concentration of salts is just around one third higher than the usual.

And this wastewater can be reused for different purposes, which effectively reduces the amount of water that is thrown away.

Is Bottled Water Better Than Reverse Osmosis Water?

From a cost perspective, it is clear to understand that RO water is much better than bottled water, as a RO system cost per year is a small fraction of the cost of drinking bottled water for an entire year.

From a health or flavour perspective it might not be so clear, but in reality RO water is typically better than bottled water. Some bottled water is less treated than RO water, so the quality of it will be less than RO water. If you drink distilled bottled water, while it should not have contaminants, it will have a flat flavour that RO water doesn’t.

And from an environmental perspective, the plastic waste that results from bottled water consumption is much worse than consuming RO water.

How Difficult is to Maintain a Reverse Osmosis System?

If you are considering purchasing a Reverse Osmosis system, it is important to understand how difficult it is to maintain it, but also how expensive it will be.

The RO membrane should be cleaned between 1 and 4 times per year, depending on the usage. You can clean them or have them cleaned off-site by a specialized company.

Typically RO membranes need to be replaced every 2 to 3 years, depending of course on the usage of the RO system.

Other components, like the pre-filters (sediment and carbon filters) and post-filter (carbon filter) should be replaced every year.

What is the Lifespan of a Reverse Osmosis System?

If you maintain your Reverse Osmosis properly, cleaning and replacing the parts with the frequency stated before, your RO system can last around 15 years.

Can I Connect a Reverse Osmosis System to My Refrigerator?

The short answer is yes, but unless you are confident in your skills, it might be better to have the help of a professional.

While installing an under-the-counter RO system is straightforward, to connect to the refrigerator you may need to connect a tube from the system and the refrigerator. You should also take in consideration the water pressure of the RO system, because it may impact your refrigerator, so always check your installation manual before.

What Next

A Reverse Osmosis system is a great option if you and your family want clean and tasty water. Not only a RO system will deliver great quality water without all the harmful contaminants, it is also easy and affordable to maintain.

If you want to understand the best Reverse Osmosis systems options for you, please check our guide.