What are the basic components of a reverse osmosis (RO) water filter?

What are the components of reverse osmosis (RO) water filter?

Reverse osmosis water filters are now everywhere. Houses, offices, markets, or hospitals- you will see them everywhere.

And, to be honest, we wouldn’t be surprised if you already have one at your home as well. This overwhelming popularity didn’t happen in a day.

The comprehensive reason behind this popularity is that RO water filters are well-known to produce the purest and cleanest water of them all. 

As RO water purifiers are becoming more and more common, it is high time you learned a thing or two about how they work. 

In this article, we’ll be discussing the basic components of a conventional RO water purifier. This will help you troubleshoot any problem you’re facing with such filters.

So, let’s go-

What is a Reverse Osmosis water filter?

Let’s first start with the definition of what a RO water filter or purifier is. 

A water filter is a device that removes pollutants from the water. Based on the process involved, there are various types of water filters these days.

One of those is the Reverse osmosis water filter. A RO water filter or purifier is the type of filter that uses reverse osmosis to purify the supply water.

Now, what is reverse osmosis? Reverse osmosis is a process in which tap water passes through a semipermeable membrane to produce purified water.

So, you see, in this case, there is a membrane. And, this one has a selective property. Not every molecule can pass through.

As you already know, tap water that we get is collected from various natural sources. Then, it goes to water treatment plants.

The plants reduce the pollutants to some extent. But, still there are some dissolved contaminants. And, the reverse osmosis membrane wipes those out.

So, you can easily realize why the reverse osmosis membrane is so vital. If you would like to know more about reverse osmosis, you should visit our post here.

Now that you know what a reverse osmosis water purifier is, let’s find out what are its basic components.

What are the basic components of a RO water filter?

In general, most of the conventional RO water filters consist of a variety of other filters along with a RO membrane.

These filters are divided into two categories. Some of those stay before the RO membrane to conduct the initial screening. The others stay after.

That’s not all. There are other vital components like the storage tank, valve, or tubing. Also, if you’re going for a high-end product, you might find some other accessories as well.

For the sake of our discussion, we’ve classified the basic components of a RO water filter into the following list. Take a look.

  1. Pre-filter
  2. Reverse Osmosis Membrane
  3. Post-filter
  4. Storage tank
  5. RO faucet
  6. Valves
  7. Tubes
  8. Accessories

Now, let’s explain these components one by one.


As we’ve already mentioned, most conventional RO water purifiers come as a combination of some other types of water filters as well.

Some of those filters stay before the RO membrane. They work to remove some of the pollutants from the tap water.

This initial group of filters is known as pre-filters. In general, there are two types of pre-filters found in the RO water purifiers that we come across in the market.

They are as follows- 

  1. Sediment Pre-filter
  2. Activated Carbon Pre-filter

Sediment Pre-filter

The sediment pre-filters are a sieve-like structure that will remove clay, sand, dust, or in general, sediment particles from tap water.

Most of us get our tap water from municipal water supplies. Some of us also get our water from underground wells.

Whatever the source is, the tap water can always come with parts of debris to some extent. This makes the water extremely unhygienic.

That’s why the sediment filter is so crucial. The filter comes with microscopic openings in it. In most cases, the openings are so tiny that dust or parts of debris cannot get past it.

The smaller the size of the opening, the higher the number of particles that get trapped. So, you see how the sediment pre-filters can get rid of the clay particles from the water.

Activated Carbon Pre-filter

Another type of pre-filter is also available. This one employs a different process than the previous one. This type of filter is known as activated carbon filters.

Most of us know a thing or two about the absorbing property of the Carbon. The Carbon filters use this property to cleanse the water.

Chunks of Carbon gets crushed and heated. This is known as activated Carbon. Due to grinding and churning, the surface area increases. As a result, absorption improves significantly.

Now, activated carbon filters are of two types. 

  1. Activated Carbon Block
  2. Granular activated Carbon

In the first one, activated Carbon molecules are set up to create a block of Carbon. As the water passes through it horizontally, pollutants like Chlorine get trapped in the layers of Carbon.

On the other hand, in granular activated Carbon pre-filter, Carbon molecules remain in a powder form. This creates more surface for absorption.

The activated carbon filters are adept at removing unhygienic organic materials, dust, rust, or other contaminants from the water. 

These two types of pre-filters are necessary to increase the efficiency of the RO membrane that follows.

Reverse Osmosis Membrane

The next component of any RO water purifier is the reverse osmosis membrane. This chamber can be referred to as the heart of these RO filters.

In the second section, we discussed what reverse osmosis is. And, the RO filters use the reverse osmosis process in this stage to purify the water.

You already know that the tap water from water treatment plants carries various pollutants to some extent. Some of those dissolve in the water while the others don’t.

Parts of debris, clay, sand, or dust fall into the category of pollutants that don’t dissolve. These get filtered out mostly by the pre-filters.

But, these pre-filters can’t remove elements that have diffused with the water. For example, ions like Floride, Chloride, Arsenic, or Lead dissolve into the water.

These ions can seep through the pre-filters. They only get caught at the reverse osmosis membrane. The selective nature of the membrane allows it to filter these elements out.

If you would like to want to learn more about how reverse osmosis works, you should visit our post here.

So, you can easily guess why RO water filters are growing more and more popular these days. That’s mostly due to this special reverse osmosis membrane.

After water gets processed in the RO membrane, it will enter the storage tank. Let’s talk about it in the later section.

Storage tank

After the reverse osmosis membrane, water gets stored into the storage tank. This reserve tank will hold water until you open the faucet.

Now, why is it necessary? The answer lies in the reverse osmosis membrane. The RO membrane requires a certain amount of water pressure to purify the water.

As water goes through the membrane, it will get rid of the pollutants and water pressure will fall at the output. This means it will take longer for the RO membrane to cleanse the water.

As a result, you won’t get sufficient water when you open the faucet. To get rid of this problem, the manufacturer provides you the RO tank.

The storage tank will continue to collect pure and clean water from the RO chamber. Inside the tank, there is sufficient air pressure.

Therefore, if you open the faucet, this air pressure will force the collected water to go out of the faucet with a comfortable flow rate. 

In this fashion, the RO storage tanks work to serve you purified water within a short period.

Are you interested to know more about the RO storage tanks, you should visit our recent article here. In this one, we’ve discussed everything about RO tanks and their working mechanisms.

Activated Carbon Post Filter

After the storage tank, comes the post RO filters. Now, when you open the faucet, water, stored at the tank, will travel through the post filter to reach the faucet.

This post-filter primarily consists of activated carbon like the activated carbon pre-filters.

In general, the post-filter performs two vital functions. Firstly, it will remove any odor or pollutant persisting after purification through the previous stages.

Secondly, if the water stays inside the tank for too long, it might grow a bad taste. The inline Carbon post-filter will remove this bad taste and give you fresh and clean water.

So, you realize, the post-filter necessarily works to get rid of the remaining pollutants and add a fresh taste into your drinking water.

RO faucet

One other crucial part of the RO water filter is the RO faucet. It works as the gateway to get the pure and clean water from the RO tank.

Now, the design of RO faucets changes from one brand to the other. It also depends on your choice and aesthetic sensation as it will stay at the top of your counter.

Therefore, the shape, design, color, and finish of the RO faucet need to complement your taste. All the RO faucets consist of alloy metals.

For example, you will find RO faucet with brushed Nickel, Chrome metal, or oil-rubbed Bronze finish. All of these comply with the food grade.

Therefore, you should go for a faucet that works well and, at the same time, enhances the beauty of your household.


To maintain adequate water pressure inside the system and regulate the flow of water throughout the system, RO filters come with a variety of valves at various points.

Among these valves, three are worth mentioning. Those are-

  1. Inlet Water valve
  2. Automatic Shut-off valve
  3. Storage tank valve

Now, let’s find out more about those.

Inlet valve

The Inlet valve is the first part of the RO water purifier. It connects to the cold water supply.

Through this inlet valve, the supply water enters into the RO system. As we’ve previously mentioned, the RO purifier requires a certain input water pressure to function properly.

For example, if the water pressure falls below 40 PSI, you won’t get enough water at the RO faucet. 

On the other hand, if the water exceeds 100 PSI, the RO membrane may get damaged.

Therefore, you see, the water pressure plays a significant role in RO water purifiers. 

The inlet valve with its pressure gauge informs about the water pressure into your system. Therefore, you see, the inlet valve and regulator control the input water pressure.

If you want to know more about the role of water pressure in your RO system, you should visit our recent article here.

Auto shut off valve

The auto shut off valve is one of the vital components of your RO water system. It stays in between the RO membrane and the storage tank.

As we’ve already discussed, the RO storage tank collects the purified water and stores it before usage. Now, what will happen if the tank gets filled?

The water will continue to go to drain and more and more water gets wasted. To solve this problem, there is the auto shut off valve and flow restrictor.

As the reserve tank gets filled with pure water from the RO chamber, the auto shut off valve will automatically shut off the input water coming into the system.

As a result, water will not get wasted. Therefore, the auto shut off valve works to maintain the efficiency of the RO water purifier.

Tank valve

Last but not least, the tank valve is another important valve for any RO water purifier. This one stays at the top of the storage tank.

As we’ve already mentioned, the RO water tank uses pre-charged air pressure to propel collected water into the faucet.

Now, if the air pressure is high enough, this will create adequate force into the water chamber and water will come out of the faucet.

But, if the pressure leaks somehow, it will not be able to create sufficient energy to defy gravity. As a result, the water might get stuck in the tubes. 

That’s when the valve works. The valve will control the directional flow of the water from the storage tank to the faucet.

Therefore, the tank valve is significant to control the output water pressure at the faucet.


The water will flow from one point to the other through the tubings. The Reverse osmosis water purifiers have various colorings of tubings to identify the connection points.

The tubes will not only differ in colors, but they also differ in shapes and diameters.

Let’s clarify it with an example. Take a look at the tubing connection in the iSpring RCC7AK RO water purifier.

Here, a black tube takes the reject water from the RO chamber to the drain. On the other hand, a red tube lets the supply water into the system.

A blue tube would connect the post-filter to the RO faucet. Meanwhile, a yellow tube will carry water from the RO membrane to the storage tank.

Therefore, you see, tubes are the necessary elements to bind all the components together. And, with this color coding, you can easily troubleshoot your installation.

If you want to take a look at some of the best RO water filters out there, you should visit our review page here.


Most of the top reverse osmosis water filters also offer one or two extra instruments to ensure the most customer satisfaction.

Two of the notable accessories that you might find in a RO water purifier are-

  1. Remineralizer
  2. Ultraviolet disinfection unit

Now, let’s discuss further on those.


The remineralizer stores back critical mineral elements into the drinking water. This, in turn, boosts your immune system and makes you healthy.

As we’ve discussed in earlier sections that the RO membrane removes dissolved ions from the incoming water. Some of these ions include Lead, Chloride, or Floride.

But, some of those ions are important for our bodies. Water from natural sources goes through the water cycle and picks up elements like Calcium, Magnesium, Iron, and so on.

The ions that we mentioned are vital for our health. All of these ions get filtered out in the RO chamber.

That’s why it is very crucial to restore these minerals into the drinking water. The remineralizer does that. As you open the faucet, water will enter the remineralizer from the post-filter.

Inside the remineralizer, various useful ions get dissolved into the water at a moderate rate. As a result, water becomes pure and healthy at the same time. 

If you’re looking for a good water filter with a robust remineralizer, you should take a look at the Aquasana OptimH2O RO water filter. Take a look here.

Ultraviolet disinfection unit

Another accessory that comes with only a handful of RO water purifiers is the ultraviolet disinfection unit. From the name, you can guess what it does.

The ultraviolet disinfection unit sterilizes your water by removing the micro-organisms from the water.

As you know, supply water travels to your home through a widely spread distribution system. In the way, it picks up various microbial life-forms like viruses or bacteria.

Some of these organisms are harmful to our bodies. The water filters cannot get rid of them. The reverse osmosis membrane gets rid of some, but not all.

That’s why you need a disinfector. In UV disinfector, it will use UV rays to modify the nucleic acids of these life forms. As a result, the pest would lose its effectiveness.

In this fashion, the UV sterilizer disinfects the water and keeps it free from diseases. If you want to know more about how UV disinfection works, you should visit our article here.

Also, if you’re looking for a RO water purifier with UV sterilizer, you should take a look at the Express water 11 Stage RO-UV water purifier. Check it on Amazon.

Final remarks

In this article, we discussed the basic components of a conventional RO water purifier. We saw how all these parts work together to serve you pure and clean water.

Along the way, we also referred you some articles which would clarify your concept about these water filters more. 

Having a sound knowledge about your RO system will help you troubleshoot any problem as you face it any day.

Hope you’ve liked this article. If you still have some questions, feel free to leave those in the comment section. We will answer those as quickly as possible.

Don’t forget to share this with your friends. Cheers!!!

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