All About Reverse Osmosis Filtration

Written by: James Smith

Updated: January 12, 2021

Heard the term “reverse osmosis” but have no idea what it’s all about? Check out our guide for everything you need to know about this effective method of water filtration.

reverse osmosis desalination plant

Water is extremely important to life on the planet. Our bodies on average are made up of about 60% water. So, it is crucial that we drink enough water on a daily basis.

Now, we understand that that’s not necessarily the easiest thing to convince people of, but, one way to make encourage your friends, family or even employees to drink more water, is by ensuring that the cleanest, purest and tastiest water is available.

Although there are places in the world where the tap water is completely safe to drink, other areas are not so lucky. That is why water filtration systems have become so popular.

With so many out there it can be hard to know which is best suited to your situation. In the following article, however, we want to show you how reverse osmosis filtration systems could be the ideal choice.

We will look at, what a reverse osmosis water system is, as well as answering the questions of how does a reverse osmosis system work and what does it remove?

To give you a balanced view of whether it is right for you or not, we will also highlight the various pros and cons of RO water systems. First things first though…

What is Reverse Osmosis?

Reverse osmosis or RO for short, is a special filtration type that involves the use of a thin, semi-permeable membrane with small enough pores for water to flow through while stopping bigger molecules, like bacteria, dissolved salts and other kinds of impurities.

It’s the simplest type of filtration process imaginable but it’s done on such a microscopic scale that it’s incredibly effective.

The process of reverse osmosis is used in the production of highly purified water for several different applications.

Common applications of RO includes seawater desalination, pharmaceutical production, cosmetics, beverages and food production, industrial boilers and the main way we are focusing on, drinking water systems. While the technology has been theorized for over a century, it has been commercially used since the 1960s.

RO Desalination Plant
RO Desalination Plant

The individual membranes are one of the most important components of a reverse osmosis filtration system. Each membrane consists of a sheet of spiral-wound, semi-permeable material and they are normally available in 8, 4 and 2-inch diameters, with the 8 and 4-inch diameters being the most common.

To ensure membranes made by different manufacturers can be used in systems, there is an industry standard when it comes to the length of 40-cm. In the beginning, the semi-permeable membranes were made from Cellulose Acetate or CA, this was changed, however, to Thin Film Composite, used over a stronger type of substrate. Today, the most commonly used membranes are made from TFC.

RO membrane diagram

How Does Reverse Osmosis Work?

Now that we’ve looked a little bit into what reverse osmosis is, to understand it better and why it is so effective, you may still be wondering how does reverse osmosis work? In the following section, that’s what we are going to discuss.

As the name suggests, RO involves the reversal of the natural principle of osmosis. That is, the natural process of water containing dissolved salts to pass throw membrane, increasing the salt concentration. This happens a lot in the natural world. Plants use osmosis to absorb nutrients and water from the soil, while in our own bodies and animal’s bodies, our kidneys use the process of osmosis to extract water from the bloodstream.

Reverse osmosis involves the use of a high-pressure pump (or simply household water pressure) to overcome the natural pressure of osmosis. This pressure pushes water containing lots of dissolved salts and other kinds of impurities into a complex semi-permeable membrane, removing an impressively high level of impurities.

Reverse osmosis membranediagram

Generally, the pressure needed will depend on the concentration of salt in the feed water. The higher the concentration, the more pressure is needed.

The desalinated water that has been deionized/demineralized is referred to as the product or permeate water. Whereas the water that carries concentrated contaminants that were not able to pass through the semi-permeable membranes is referred to as the concentrate or reject stream.

The concentrate containing all the salts and impurities that were prevented from passing through the membrane are then either passed through the filtration system to be drained away or through to other processes.

You can read all about the installation process here.

What Does it Remove?

Now you understand a bit more about how it works, it’s time to look at another pertinent question with regards to this kind of water filtration. That is, what does reverse osmosis remove?

Generally, this form of filtration can remove around 99% of all dissolved salts, pyrogens, bacteria, organics, colloids and particles present in the feed water. That doesn’t mean it should be relied on as the main way to remove viruses and bacteria from the water, though. These types of contaminants should be treated with a good UV filter. You can learn more about UV filtration in our guide.

Water pollution cycle

The membrane used in the system is designed to reject contaminants based on charge and size. For instance, any contaminants that have a greater molecular weight than 200 are normally rejected if the system is running properly. As a rule of thumb regarding the ionic charge of contaminants, the higher it is, the less likely it will be to pass through the membrane.

However, some of the most common contaminants that are reduced or removed in a good quality reverse osmosis system include:

  • Lead
  • Mercury
  • Turbidity
  • Aesthetic Chlorine
  • Aesthetic Chloramines
  • Cysts
  • Sediment
  • Volatile Organic Compounds
  • Particulate Class 1
  • Another 90+ contaminants

There is a downside to being so effective at removing objects from the water. RO has no way to distinguish between good and bad particles. So, that means even healthy minerals like magnesium and calcium are removed from the water too. Therefore, RO water is free of healthy minerals and can be slightly more acidic due to the lack of their presence.

Thankfully, there’s a pretty simple workaround for this. The top household RO systems include something called a remineralization filter. This adds minerals back into the water after they have been stripped away by the membrane. This means reverse osmosis water can be great tasting and full of minerals as well as being free of harmful contaminants.

Related: We explain the specific contaminants that reverse osmosis filtration removes in more detail.

Pros and Cons of RO Filtration

When looking at anything in life, whether it’s a new deodorant, car or, yes, water filtration system, you need to consider both the pros and the cons. No system is ever going to be 100% perfect, so it helps you to make the best decision about what is right for you by assessing it in a balanced way.

Therefore, in the next section, we are going to discuss the many pros and cons of RO water filtration, as well as debunking a few false claims along the way.


  • Removal of contaminants – Perhaps the most crucial reason most people invest in RO systems in the first place is that that they are very effective at removing, as noted earlier, around 99% of the majority of dangerous and toxic contaminants.
  • Fully tried and tested technique and technology – As reverse osmosis is used in various industries, including bottled water (for soft drinks, sodas and energy drinks), wine (removal of taint and wine concentration), dairy (milk concentration) and supplement (whey protein production), it is a very trusted and tested process. In fact, it is likely that you have drunk many products that RO is involved in the production of and didn’t even know it.
  • Enhanced water flavor – Even if you have been a long-term fan of tap water, if you’ve had the pleasure of drinking it from a system that has a higher quality of water, purified water will always taste better. It does not have an unpleasant or odd taste, odor or even aftertaste. The absence of chlorine makes a huge difference to water.
  • No need for plastic bottles – We have a plastic pollution epidemic on our hands throughout the world. One way you can become part of the solution is to avoid using plastic bottles. Having a reverse osmosis water filter would mean you don’t have to get water from anywhere else. As well as helping to save the environment, you would also save a lot of money.
  • False Claim – RO purification does not consume energy – Although the above pros are all genuine and accurate, there is a misunderstanding that reverse osmosis systems do not use energy to operate. However, this is simply not true. Even systems that don’t connect to a power supply of some kind, still utilize energy taken from the water pressure of your property’s system.


  • Long process – Although it depends on the water pressure of your property, using reverse osmosis is a long process that you need to have patience when using. It can often take a full day to completely fill the water tank because only trickles flow out.
  • Wasted water – Every gallon of water that is successfully purified using RO results in at least 1 gallon of wastewater. This obviously adds to the costs.
  • Upfront costs – Speaking of costs, the upfront expenditure on a reverse osmosis filtration system for a whole house or building is going to cost more than $500. The systems themselves are not the only cost though, as they require comprehensive installation, which means you would have to hire a professional. Unless you are an experienced and qualified plumber.
  • Dead water – As well as all those nasty contaminants like pharmaceutical residues and mercury, etc., RO systems also remove crucial minerals that you need. That being said, according to the WHO and the Water Quality Association of the US, 95% of the RDA of minerals is derived from the food we eat. The exceptions are magnesium and calcium, with 20% of their RDA coming from drinking water.
  • Unpleasant smell and taste – Although we have already noted in the pros section of this article that RO systems remove unpleasant smells and tastes, the opposite could still apply. If an RO system is not a modern one and has damaged membranes, it could still produce water with a bad smell or taste. What’s more, when bacteria accumulates inside your purification unit, it not only makes the smell and taste worse but also presents a health risk.
  • MaintenanceMaintenance of RO systems needs to be carried out fairly regularly, including replacing the post and pre-filters and semi-permeable membranes 6 to 12 months, and the complete sanitization of the tank and system at least once a year.
  • False claim – RO filtration produces harmful acidic water – It’s true that when reverse osmosis water filtration removes the majority of the metals and minerals in the water, it leaves a solution that is slightly more acidic. However, the pH is only going to change very slightly.


When it comes to investing in any special water systems for your property, whether it’s your home or business premises, you need to put a lot of thought into your decision. Most water filtration systems, like reverse osmosis systems, can be rather expensive.

As all water filters and technologies used in this kind of process have their plus points and negatives, we also highlighted the many pros and cons of reverse osmosis systems. This helps to give you a more balanced view, rather than just focusing too much on the good things without mentioning the bad. The important thing to remember is that no system is 100% perfect.

When it comes to deciding if a reverse osmosis system is right for you therefore, you need to weigh up everything related to it. You need to think about the installation, the costs involved, how effective it will be with your current water system and pressure and whether any potential downsides are minor enough that you can look past.

If you do though, we are sure you will find that a reverse osmosis water purification system will help to produce that great tasting, healthy water you’ve been looking for. You will spend less on plastic bottles and you may even be able to encourage your family members, young children or colleagues to drink more water, resulting in a building or household with happier and healthier inhabitants.

About the Author James Smith

James is the chief water geek here at His mission is to empower the consumer and allow people to take control of their health. His passion for water health is contagious, hopefully unlike your tap water!

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