what is air and water pressure in reverse osmosis (RO) water filters?

What is air and water pressure in reverse osmosis (RO) water filters?

Nowadays, you will find water filters almost everywhere. Most of those fall into the same category; many of those are reverse osmosis (RO) water filters.

Due to the high-quality water they provide, this type of filter has become very popular over the years. These products also tend to sustain for a long period.

As these filters are a very common figure these days, you need to know some of the basic concepts about this device.

All of the reverse osmosis water purifiers use water pressure and air pressure alternatively to provide purified water through the faucet.

In this article, we’ll be shedding light on the working mechanism of RO water filters and how water and air pressure play a significant role in the filtration system.

If you’re curious to know more about these facts, stay with us. We hope to answer all your questions. Let’s go.

What is the water pressure and how can you measure it?

Before we dive deep into the topic, let’s first clear our thoughts on what water pressure is and how you can measure it.

According to physics, “Pressure” is defined as the amount of force applied on a surface with a unit area. So, water pressure means the force water deploys on a surface.

Most of us get our water from municipal water supplies. The water reaches us through a complex distribution system.

This flow of water creates a force on the wall of the pipes. Therefore, as soon as we open our faucet, water comes out with full force.

Now, the value of water pressure differs from city to city, from town to town. It also can change during the time of the day.

For example, during the daytime, water pressure may be less than that during the night when people are not using water that much.

The international unit to measure pressure is Pascal, Pa. But, when you’re measuring the water pressure at your home, you will be using another well-known unit, PSI.

PSI means pound per square inch. If you’re curious enough to find out the feed water pressure at your home, you should use a pressure gauge.

The pressure gauge is a device that can measure the water or air pressure in units of PSI.

In general, the feed water pressure at your home should stay above 40 PSI. If you measure a value below that, you should contact your local authority to look into the matter.

How does water pressure influence the purification process in a RO filter?

Now, that you know the basics of water pressure, let’s see how it influences the RO water filters when those are purifying our drinking water.

The RO water filters use a special technique, reverse osmosis to remove the dissolved particles from the water. In this process, water is forced to pass through a membrane.

The membrane has a selective property which only allows the water molecules to seep through.

As a result, when the water enters the RO chamber, the pollutants get cleansed. And, we get purified water as output.

If you want to know the details about how RO water purifiers use reverse osmosis to sanitize water, you should visit our post here.

One thing that you need to know about Reverse osmosis is that it requires a minimum pressure that forces the RO membrane to perform its job.

This pressure exerts a force on the membrane and, in turn, the membrane can repel the osmotic pressure. If the pressure is high enough, water molecules can also go through.

So, you can realize, this pressure is very crucial to keep the RO chamber functioning. That’s why you need to check the input water pressure before the RO chamber.

If the pressure is not enough, you will have complexity using your water filter, for example, there will be slow flow at your filter’s faucet.

You can check out our article where we discussed why the slow flow of water occurs at the RO water filter’s faucet. Check it out here.

What is the typical value of the input water pressure at the RO membrane?

Now, that you know RO membranes require input water pressure to be within a certain range, let’s look more into this.

In general, conventional RO water filters require incoming water pressure to be within 40 PSI to 100 PSI to work properly. 

If the water pressure goes below 40 PSI, it wouldn’t be able to force the water molecules to pass through the semipermeable membrane.

On the other hand, if the water pressure goes above 100 PSI, it might damage the RO membrane over time. In this case, the membrane will not sustain its typical lifetime.

Therefore, you need to make sure that the input feed water pressure at the RO membrane is higher than 40 PSI but lower than 100 PSI. 

Now, let’s take a look at the recommended level of water pressure for the best selling RO water filters.

One of the top RO water filter producers, iSpring recommends that your incoming water pressure should be within 45 to 70 PSI.

Another pioneer in this field, APEC, suggests that the incoming water pressure should not be less than 30 PSI. The ideal water pressure should be 60 PSI.

On the other hand, Home Master requires that the incoming water pressure be higher than 40 PSI to make its water filters efficient in purification.

Name of the brandMinimum Required water pressure
iSpring RO Water filters45 PSI
APEC RO water filters30 PSI
Home Master RO water filters40 PSI

How can you regulate input water pressure at the RO membrane?

We have seen in the previous section that the incoming water pressure at the RO membrane should be around 40 to 100 PSI. But, sometimes, the feed water pressure is not within this limit.

For example, in some municipalities, water pressure can be lower than 40 PSI. As a result, the RO water filters fail to purify water at the required rate, and you don’t get water in time.

Therefore, you can see that low input pressure is one of the reasons behind slow flow at the faucet. You can check out our article here to find out the other ones.

So, what should you do if the water pressure is below 40 PSI? Firstly, you should contact your water service provider. Another possible solution is to use a booster pump.

You just have to install a booster pump in front of the RO membrane. This will increase the water pressure at the input of the RO chamber.

Now, what should you do if the water pressure is over 100 PSI? In this case, you should use a pressure regulator.

The pressure regulator will moderate the speed as your requirement and keep it in the comfortable range for the RO filter to work.

So, you see, if the water pressure is too low, you should use a booster pump in front of the RO membrane. On the other hand, if the pressure is too high, you should use a pressure regulator.

How does the air pressure influence the flow rate at the RO faucet?

Not only the water pressure but also there is air pressure associated with a RO water filtration system. Now, let’s look into that.

Air pressure- like water pressure is the amount of force that air applies on a surface. Therefore, we also can measure it with a pressure gauge.

Now, let’s see how the air pressure helps you get purified water from the RO system. We all know that a RO water filter uses a storage tank.

Water that enters into the RO membrane gets purified. This purification through the membrane takes time. 

To account for the latency, a storage tank comes with the package where the filter stores the purified water for later usage.

Now, the product water from the RO membrane keeps gathering inside the tank. 

Normally the tank stays below the sink. Therefore, when you open the faucet, the water has to travel against gravity to come out of it. This requires energy.

The storage tank consists of two portions. There are two separate chambers- an air chamber and a chamber for the purified water. In general, a diaphragm stays in the middle.

Now, as more and more water enters the water chamber, it continues to put pressure on the air chamber. After the water chamber gets filled, the air pressure is at the maximum.

Now, as soon as you open the faucet, this air pressure releases some energy and pushes the purified water to the faucet against gravity. 

So, you realize, the air pressure is an integral part of the RO water filter to work properly.

What is the typical value of air pressure in the storage tank?

So, coming from the previous section, you can easily guess how the air pressure can regulate the water flow rate at the faucet.

If the air pressure is significantly low, this will not be able to propel the purified water through the faucet.

Therefore, there should be a sufficient amount of air inside the air chamber. Otherwise, you will get a moderately slow flow of water at the faucet, even in the worst case, there will be no water at all.

Now, how much pressure should be there to regulate the water flow at the faucet?

The answer differs from one product to the next. In general, most water filters require air pressure to be within 5 to 10 PSI in the storage tank.

Now, let’s take a look at some of the best RO water products and what they suggest.

One of the top brands, Whirlpool recommends that there should be an air pressure of 5-7 PSI inside the tank.

Express Water System suggests that the pressure should be about 8-10 PSI while another well-known brand, APEC would advise you to keep the air pressure within 5-7 PSI.

All this info is compiled here in the table below.

Name of the brandThe pressure at the RO storage tank
APEC RO water filters5-7 PSI
Whirlpool RO water filters5-7 PSI
Express Water System RO water filters8-10 PSI

How can you increase air pressure in the storage tank of a RO filter?

From the previous section, you can see that the air pressure in the storage tank should be between 5-10 PSI.

Newly installed RO filters will provide you a storage tank that already has a pre-charged air pressure within the allowable range.

But, as you continue to use the product, the air pressure can go down gradually. As the filter ages, some air might leak. As a result, pressure can decrease to some extent.

So, what should you do if the pressure lowers below 5 PSI? Firstly, you should check it with a pressure gauge.

Now, if the air pressure is really low, you should open the air pressure valve. Then, you should add some air into the air chamber. You can attain this using a normal cycle.

Make sure the pressure is within the allowable limit. After you do this, make sure you close the air chamber valve tightly. 

In this fashion, you can regulate the air pressure and make sure there is enough flow at your water filter’s faucet.


Throughout this article, we tried to discuss everything you need to know about water and air pressure and what their roles are in a RO water filter.

You have seen how the input water pressure can influence the Reverse osmosis membrane’s capability to purify your drinking water.

We have also discussed how the air pressure inside the storage tank can regulate the water flow at the RO filter’s faucet.

We hope we’ve covered all your questions regarding water and air pressure in a reverse osmosis water purifier.

So, what do you think? Did you like the post? Or, you still have some questions unanswered. Let us know those in the comment section.

You can visit our blog page to find out more informative articles like this. Cheers!!!

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