How Reverse Osmosis Water Filtration Works

After learning about all of the dangerous contaminants and pollutants that are present in drinking water, I started to wonder how does reverse osmosis filtration work? I knew that I had to learn more and to provide my family with safe water so that we weren’t accidentally drinking something that could be dangerous.

After reading this article you will understand how reverse osmosis systems work, what impurities they remove from drinking water, and how each component works.

While it sounds involved and a little difficult to understand, reverse osmosis is actually a very simple water filtration process that will remove the contaminants and pollutants that are in your water so that you and your family are not drinking them. 

Unlike other water filters that rely on gravity to move water through a filter, reverse osmosis relies on water pressure to force water through a filter, or a semipermeable membrane, that is fine enough to remove most impurities from your drinking water.

Unlike regular osmosis, where water will naturally pass through a membrane to an area with more contaminants, in reverse osmosis the water is forced to travel the other way. This means that those contaminants and pollutants are left behind on one side of the membrane and that you are able to enjoy very clean and safe water.

How Does Reverse Osmosis Work?

reverse osmosis system

Most people remember from high school chemistry classes that osmosis is the process through which molecules of a substance, often water, pass through a membrane to travel from a less-concentrated solution to one that is more concentrated. This would result in the water having more contaminants in it, which is why you need to reverse the process.

Molecules of water are pushed at high pressure so that they can pass through a strong, durable, and specially designed membrane. This semipermeable membrane is heat resistant, incredibly strong, and won’t be affected by chemicals. 

The membrane is designed so that the water molecules are the only ones that can pass through. All contaminants and pollutants will not only be left behind and collected, but also flushed away so that they are not passed back to your drinking water supply.

Benefits of Using Reverse Osmosis Water Filtration

It’s always a good idea to educate yourself about the pros and cons of various systems that you want to use in your home. Reverse osmosis water filtration systems offer a number of benefits, which is why they are becoming so popular with people who want to improve their health and make sure that they are drinking the best possible water. 

These include:

        The process removes dangerous contaminants

        It reduces the sodium that is found in soft water

        You won’t have to keep buying bottled water

        It’s better for cooking, as your water won’t affect the taste of your food

        You will have completely clear ice cubes

        This water tastes amazing

Reverse Osmosis System Components

reverse osmosis components infographic

It can be easy to get overwhelmed when researching reverse osmosis systems, especially because they involve a number of different components that have to be used together for the system to work correctly. Here you can see the components and their primary function.

Line Valve – this is the valve that intakes all of the water that will pass through your reverse osmosis water system. It connects to the cold water supply line.

Pre-Filter – before water can pass through your membrane filter, it has to first pass through at least one pre-filter. These filters remove larger contaminants from your water that could otherwise damage your system. You can use more than one filter if you also want to remove chlorine.

Reverse Osmosis Membrane – this is the semipermeable membrane that can easily remove the contaminants from your water. The majority of all water filtering occurs here.

Post-Filter – most contaminants in a water supply will be removed by the membrane, but some can be missed. This filter will easily catch any other additives in the water that passed through the semipermeable membrane.

Auto Shut-Off Valve – after filtering, all water will pass through into a storage tank, but it’s important that this tank doesn’t accidentally overflow. These shut-off valves not only gauge how much water is in the storage tank, but will stop water from entering when they are too full.

Check or Retention Valve – this valve is at the end of the housing for the semipermeable membrane, and its one job is to make sure that no treated water flows backwards from out of the storage tank. Any backward flowing water could easily and quickly rupture the semipermeable membrane.

Flow Restrictor or Regulator – this component is used to keep water flowing through the membrane at the right speed. If the water is flowing too slow, then you will not have very much drinking water produced and the water will simply flow through the drain line instead of being passed through the membrane.

Storage Tank – these can vary in size, but most storage tanks hold anywhere from two to four gallons of water. There is a bladder inside the tank that ensures that the water is pressurized when full.

Faucet – to access your newly filtered water you will need to use the faucet that connects directly to the storage tank. This is generally installed near the kitchen sink to make it easy to use.

Drain – at the outlet end of the membrane is a drain line that is used to dispose of the water that contains the filtered out contaminants. This water easily passes through the drain so that it doesn’t come near your filtered water and accidentally contaminate it again.

Contaminants Removed from Water by Reverse Osmosis Filtration

Once you start learning more about reverse osmosis water systems, you will be surprised at all of the different contaminants that they can remove from your drinking water. The list includes more than 100 different contaminates from your drinking water, which include:







        Nitrates and nitrites






        Other total dissolved solids

11 Most Asked Questions About Reverse Osmosis

1) What Happens to the Contaminants That Don’t Pass Through the Membrane?

Most of the water that passes through a reverse osmosis water system will be filtered through the membrane and then moved into the storage tank so that you can drink it later. This is great, as it means that you won’t have any contaminants in your water, but it’s normal to wonder where they go.

I used to think that they would simply build up on the membrane, which I didn’t think could be healthy or safe. Luckily, this is not what happens.

There is a stream of “reject water” that is redirected from the membrane and down through the drain. All contaminants fall into this water stream and are removed with it. 

This allows all of the contaminants that your system removed from your water to be disposed of so that you don’t have to worry about them accidentally contaminating your safe drinking water.

2) How Does a Reverse Osmosis Membrane Work?

Unlike with regular osmosis, where clean water will pass through a membrane and try to join the dirty water, with reverse osmosis you take control of this to ensure that your clean water isn’t affected.

These membranes are similar to screen doors, but they have a mesh that is much, much smaller so that water cannot pass freely through it all of the time.  

The semipermeable membrane allows water to pass through while blocking contaminants, just like a screen door allows air through, but stops flies and other insects from coming inside.

These membranes are generally made up of polyimide, which is a very durable and strong plastic resin that can easily stand up to its job without being damaged. These membranes have an active barrier that allows submicron filtration, as well as a support layer, that prevents damage to the membrane.

3) How many types of Reverse Osmosis Drinking Water Systems and Filters are there?

There are a few different types of RO systems to consider for your home. Under the sink systems are the ones that most people are familiar with. These are generally installed in the kitchen and allow access to clean and filtered water on demand for drinking and cooking. 

The whole house system is installed at the home’s main water line and treats all of the water in the house, no matter if you will use it for cooking, cleaning, or washing clothes.

Countertop, or portable, RO systems can be installed anywhere in your home, making them very convenient and great for traveling, but they won’t be able to filter as much water in a short period of time as a larger system can.

Tankless systems are countertop and produce water that pours directly into a container. I think that they are a great option if you don’t want to have to wait on having clean water and if you have limited space where you can put your new system.

4) How Much Service and Maintenance Does an RO System Require?

Just like any other system in your home, you do have to perform routine maintenance on these systems to keep them working their best. 

The pre-filter in your system can become clogged easily as it filters out larger contaminants from your water. You will want to change this filter every six to nine months to prevent it from failing you and not being able to protect your semipermeable membrane.

Any carbon filters in your system that are designed to remove chlorine also need to be changed every six to nine months to keep them working their best.

The RO membrane, or semipermeable membrane, in your system has a much longer lifespan. This membrane can last for around two to three years without failing you. 

However, I think that it’s important to note that this is really only a guideline. Your membrane can last a shorter or longer period of time, depending on how much your household uses the system, as well as your local water conditions, as they can have a huge impact on the life of your membrane.

5) Where Is an Reverse Osmosis System Stored?

Where you have your RO system stored will depend on the type that you buy. The most common types of systems that go in the kitchen can easily be stored underneath the kitchen sink. Larger systems won’t fit there and will require more storage space, while portable and countertop systems can be placed on the countertop so that they can be moved out of the way when you need more space.

6) Can an RO System Be Connected to My Fridge or Ice Machine?

Yes, you can have your under-counter system easily connected to your ice maker or your fridge so that you don’t have to worry about the cleanliness of your cold drinking water or your ice cubes. In fact, whole-house systems will automatically be connected.

It’s a good idea to hire a professional to connect your RO system to your fridge. They can easily run a tube from your system and connect it to the back of your ice maker or your fridge. You want to hire a professional so that they can make sure that the pressure from your unit is correct. 

7) How Much Water Can an RO System Produce Each Day?

Every system is going to be able to produce a different amount of water, which is why it’s a good idea to learn how to determine how much your RO system can produce. 

The equation for this involves measuring how much water in millimeters the system produces in one minute, and then multiplying that number by 0.38 to convert to gallons a day.

It’s amazing how widely production can vary. Some units only produce 16 gallons of purified water in a day, while others can produce 75 gallons

8) Is a Reverse Osmosis System Noisy?

This is a concern that a lot of people, myself including, have when considering a reverse osmosis water system, but you don’t need to worry. 

While there is a slight humming when the water is being processed, these systems aren’t at all noisy. 

Some other normal sounds that you may hear include the whining of the tank coming to pressure when you first install your system and a slight dripping from the drain when the water is rejected.

9) Do You Need Electricity to Operate RO?

These systems actually rely on water pressure, not electricity, to operate. If you want to upgrade your system, such as with an electric pressure boost pump or even an ultraviolet lamp, you will need electricity.

Not having to have electricity to operate these systems is one of the perks that people enjoy. 

10) How Long Will a Reverse Osmosis System Last?

As a whole, a reverse osmosis water system should last around 10 years, although 15 is entirely possible. This is only if you regularly service and maintain your unit, change your filters when you are supposed to, and clean or sterilize the entire system on an annual basis.

Owners who don’t take care of their systems will find that they fail much faster and will need to be replaced. If you don’t replace your filters or maintain your system, then you will notice that you are producing less water until you aren’t producing any at all.

11) Will Reverse Osmosis Remove Minerals That Are Healthy to Keep Minerals in Water?

One concern that some people have is whether or not a reverse osmosis system will remove beneficial minerals from the water. At the same time that it is removing harmful chemicals it will remove minerals. 

This used to bother me until I realized that there are not very many minerals in water. When you realize that you don’t get very many of your necessary minerals each day from water, then you stop worrying so much about the minute amount that are removed, as most of your minerals come from supplements and foods.


Reverse osmosis water filtration systems offer numerous health benefits and are, hands down, the best way to improve the safety and purity of your drinking water. If you’re concerned about the pollutants that you’re drinking each day and want to provide yourself and your family with better water, then it’s time to consider one of these systems. 

I love how mine helps keep my water cleaner than ever before, which gives me peace of mind about what I’m putting in my body. This is especially great if you live in an area where the water quality is questionable and you want to take matters into your own hands.

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