Reverse Osmosis Storage Tank

A reverse osmosis storage tank is a pressurized container within the RO system that’s used to hold the finished purified water after the filtration process through the RO membrane.

In this article, we are going to give you a quick review of the 10 best reverse osmosis storage tanks – as known as RO pressure tanks.

We also give you an insight into everything to do with the reverse osmosis tank (RO pressure tank) including how they work, and RO storage tank replacement.

10 Best RO Pressure Tanks In This Review

RO TankStorage Capacity
iSpring T32M3.2 gallons
tankRO GTS64.4 gallons
CRYSTAL CLEAR TKE1410.3 gallons
APEC Water TANK-43.2 gallons
PA-E PRO 1323.2 gallons
Charman 4 Gallon3.2 gallons
PAE RO-1222 gallons
Geekpure 2.8 Gallon2.8 gallons
Express Water V-RO132-TNK3.2 gallons
iSpring T20M14 gallons

iSpring T32M RO Storage Tank

iSpring T32M

The iSpring T32M is one of the best RO storage tanks out there for residential Reverse osmosis systems. It’s well-designed and functions very well with most RO systems.

It’s a 4-gallon Reverse Osmosis Storage Tank and can hold up to 3.2 gallons of filtered water when full which is a pretty decent amount for residential use.

The tank comes pre-pressurized between 7 to 10 psi and has a maximum working pressure of around 100 psi. Therefore, it can work pretty well with municipal feed water pressure as well as a boost pump.

The T32M is a perfect RO replacement tank for diverse use as it discharges effectively in both vertical and horizontal positions. It comes with a tank stand which you can use for either the vertical or horizontal position.

The water chamber is a high-quality, FDA-grade butyl diaphragm that has gone through special post-cure procedures to make sure that the water held in the tank remains safe, tasteless, and odourless.

The inlet/outlet valve connection of this iSpring reverse osmosis storage tank is also made of stainless steel. It won’t strip or break easily and it does prevent contamination by lead leaching.

The connection fits the standard ¼“NPT thread ball valve which is fortunately included with the tank. The unit also has a standard air nozzle at the bottom part which you can use to adjust the air pressure inside the tank if needed.

In short, the iSpring T32M is a superb storage tank perfect for use with under-sink RO systems and has enough capacity to meet the daily clean water demand in a household.

tankRo 4 Gallon RO Storage Tank

tankRo 4 Gallon

Following the iSpring T32M is the tankRo water storage tank which is yet another quality and highly-reliable RO storage tank for replacement on the market today.

When you look at it, it’s much similar to the iSpring T32M in terms of design and physical specifications. It features a 4-gallon storage tank with a water chamber area that can hold a maximum of 3.2 gallons of water at one time.

The rest of the storage area is occupied by the air bladder which has been pre-pressurized to help in drawing water from the tank. It comes pre-charged at 7 psi and has a maximum working pressure of up to 100 psi.

The great thing about this tankRo storage tank is that it’s well-designed to ensure consistent air pressure. It has a sealed brass air nozzle with o-ring air valve caps which not only prevents the loss of air from the vent but also keeps the diaphragm from damage.

This tank is also made to ensure you get clean and contaminant-free water that always tastes fresh and pure. The inside line of the water chamber is made from high-quality virgin polypropylene which is a smooth and durable liner.

The liner ensures that the remains odourless, tasteless, and free from contaminants while in the tank. The diaphragm is a post-cured Chlorobutyl rubber which also means no chemicals leak into your water, so it remains safe and clean inside the tank before drawing it.

The inlet/outlet connection is strong stainless steel and it can fit a ¼” NPT valve which is as well included in the package.

Overall, the tankRo reverse osmosis storage tank has heavy-duty construction and can last many years. It’s a reliable and fully functional RO storage tank that would fit under most kitchen sinks. It also comes with a stand that you can use to secure it.

APEC Water Systems TANK-4

APEC Water Systems TANK-4

The APEC TANK-4 is a standard RO tank that offers a quality water storage option to ensure a consistent supply of water to your household.

Like the other two models above, this one too is a 4-gallon tank which is capable of holding up to 3.2 gallons of water when it’s completely filled.  That’s enough capacity to cater to the needs of most small to average families.

The unit discharges water efficiently whether it’s placed in a vertical or horizontal position and it features a stand to allow you easily and comfortably use the tank in both positions.

It comes pre-pressurized to around 7 psi and can equally operate at a maximum pressure of 100 psi.  It’s effectively designed to provide airtight protection against leaks as well as contamination.

The shell is constructed from heavy-duty stainless steel which surrounds a fully enclosed virgin polypropylene liner and high-grade, post-cured butyl diaphragm. This robust and very efficient construction ensures zero leaks and eliminates all risks of contamination.

Therefore, when you open the faucet, you can expect to get tasteless, odourless water that’s clean and free from contaminants.

The connector is made from stainless steel, so no leaching either and it’s compatible with the standard ¼” RO tank ball valve. Quality, safety, and durability are what this APEC TANK-4 offers, and it is another great option for replacing a faulty old tank.

Purenex PRO RO Storage Tank

Purenex PRO

Purenex PRO is an equally great replacement tank for any residential RO system. It’s a compact but quality unit that’s built to integrate and function smoothly to deliver clean water.

Being a standard 4-gallon tank, the Purenex PRO can comfortably hold about 3.2 gallons of purified water which is sufficient to maintain a continuous and stable supply suitable for small to average size families.

The air bladder comes pre-charged with around 5 to 7 psi of air pressure and when the tank is filled up, the pressure may reach 30 to 50 psi depending on the pressure of the feed water supply.

Inside the tanks is a fully enclosed polypropylene liner which forms the upper compartment of the water chamber. A post-cured butyl diaphragm separates the water chamber and the air bladder.

These materials are approved for safety and quality. They eliminate the possibility of odours and a metal taste in the water as well as provide airtight protection against contaminations and leaks.

The water inlet/outlet thread is also made of stainless steel to prevent leaching and it will fit a standard ¼” MPT ball valve.  

Installation is pretty easy and you can as well easily re-pressurize the tank using an air pump just right through the air valve below the bottom bladder.

Charman Manufacturing 420005 RO Storage Tank

Charman Manufacturing 420005

Taking the fifth spot on our list is the Charman Manufacturing 420005 storage tank. This is another quality unit and a very good replacement for a damaged or old RO storage tank.

To start, the water chamber of the tank can hold a maximum of 3.2 gallons which is a standard capacity we’ve seen in all the other four models reviewed above.

The air chamber, on the other hand, comes pre-pressurized to around 8 to 10 psi but once hooked the water storage pressure can be around 40 to 55 psi. Therefore, it can work well with the normal pressure on city water which is about 60 psi, or even a maximum pressure of 100 psi.

The overall construction is quite robust too with a high-grade steel shell that covers a polypropylene line and a butyl rubber diaphragm which forms the water chamber.

All these materials are of good quality and CE-approved which guarantees the quality and safety of the water that’s stored inside the tank and delivered to your tap when you open the faucet. They eliminate contamination and the possibility of odours. 

The stainless steel connector is compatible with the ¼” NPT ball valve and the whole tank is a breeze to install. It would take only a few minutes to set it up as long as you got some Teflon tape.

It looks good and works great. The Charman Manufacturing 420005 storage tank is an ideal choice for average to large families. It ensures a continuous supply of filtered water at a decent rate. The only downside is that it doesn’t come with a new shut-off valve.

Geekpure RO Water Storage Tank

Geekpure RO Water Storage Tank

The Geekpure RO storage tank is a small and compact unit but still very functional and a nice option as a replacement tank for most home RO systems.

It can hold up to 2.8 gallons of purified water which is small compared to what the other units above offer but it’s just enough to meet the daily needs of small to average families. Its compact design allows it to easily fit under a sink or a place with space constraints.

The pre-charged pressure when the tank is empty is 5 to 7 psi and the tank can work with a feed water pressure of up to 100 psi.

The outer shell of the tank is made of durable stainless steel while the water chamber consists of a full food-grade polypropylene liner with a butyl diaphragm. Therefore, no chemicals, unpleasant odour, or taste are going to be in your drinking water.

Same as the other storage tanks, the connector on this one is made of stainless steel and it will fit any ¼” NPT ball valve which is not included with the tank.

In general, while it may seem small in terms of capacity and size, this Geekpure RO storage tank will get the job done as far as storing and delivering clean water is concerned.

It delivers water at a stable yet fairly fast rate making it a wonderful option for small families that have an RO system installed in their homes.

tankRo GTS6 RO Storage Tank

tankRo GTS6 RO Storage Tank

If your current RO tank is small and you are looking for a great replacement tank that will give you a little more capacity yet still fit under the sink, then the tankRO GTS6 storage tank might just be the right choice for you.

This is a 6-gallon RO tank that can hold up to 4.4 gallons of filtered water which is a fairly large capacity that can comfortably serve average as well as big families.

The tank arrives pre-charged at 10 psi with the inside completely smooth to prevent any damage to the bladder.

The inside liner that makes up the water chamber is made of virgin polypropylene while the adjustable bladder is a high-grade Chlorobutyl rubber that’s totally airtight.

Generally, all the components are of high quality and FDA grade and 100% food-safe hence the water will remain completely clean in the tank without any chances of contamination.

The overall construction is also heavy-duty with the exterior part of the tank consisting of a two-part epoxy primer coating that’s finished with polyurethane.

Therefore, it’s not only designed to resist damage but to also last for even more than five years. You get a free ¼” ball valve together with the tank and a stand also to help secure it in the right position.

If you’ve been struggling with the small capacity of your current RO tank, then we would recommend checking out this tankRO GTS6 storage tank because you won’t have to worry anymore about running out of fresh water. 

iSpring T20M RO Storage Tank

iSpring T20M RO Storage Tank

The iSpring T20M is a perfect choice for anyone seeking a much higher capacity to add to their residential or commercial RO system. It’s a tank that you can use with your under-sink RO system or as your whole house water storage with the existing RO system.

The unit is a 20-gallon tank with a capacity to hold up to 14 gallons of water making it the largest capacity on our list.

Its big-sized water chamber makes it an ideal choice for larger households whose demand for clean water is high or for commercial RO systems that are required to constantly supply clean water in fairly large volumes. You can fill 8 gallons at one time and still have more water left over.

The bladder air pressure when you get the tank is about 7 psi at the minimum and about 10 psi maximum. This is when it’s empty but its maximum working pressure is around 100 psi.

Whether placed horizontally or vertically, the tank discharges efficiently. Plus both the post-cured butyl diaphragm and the polypropylene liner are FDA-listed, food-grade materials which means a contaminant-free water chamber that ensures a tasteless and odourless water supply.

The tank features stainless steel connector like the rest but it uses a 3/8″ shut-off valve which both are not included with the tank. Nonetheless, if it’s a larger capacity you are after, then this might be the best choice.

CrystalClear RO Storage Tank

CrystalClear RO Storage Tank

The CrystalClear RO storage tank is another large-sized tank that’s specially designed for residential RO systems.

It’s not as large as the iSpring T20M as it can easily fit under your sink but it does offer plenty of capacity than all the other tanks apart from the T20M of course.

The unit can hold up to 10.3 gallons of water with ideal pressure which gives you plenty of purified water ready to go whenever you want. With this capacity, you can fill several gallons of jugs without causing any slowing of flow.

The tank’s air pressure when it’s new and empty is around 7 psi which you can fill up to not more than 10 psi. When the water chamber is full, the air pressure is about 30 to 40 psi, so it can effectively work with a feed water pressure of 60 to 100 psi.

The discharge is as well efficient in both vertical and horizontal positions and unlike the other models, this CrystalCLear tank has its air valve mounted on the side which is quite convenient in terms of adjusting the air pressure inside.

The water chamber is made up of a virgin polypropylene liner and butyl diaphragm which as mentioned several times in the other reviews are food-grade materials that ensure tasteless and odourless water.

To sum it all up, this is a quality tank with sufficient capacity to meet the need of almost any residential household. If you need a larger replacement tank that can fit under your sink, then this is also worth checking.

 PA-E RO-122 Water Storage Tank

 PA-E RO-122 Water Storage Tank

Closing our top 10 best RO storage tanks list is the PA-E RO-122 which is a compact unit specifically designed for those seeking a small, space-saving solution for their small household.

The tank has a capacity rating of 3 gallons but the water chamber can hold a maximum of 2 gallons. It’s the smallest capacity compared to the rest but it’s enough for one or two people.

The compact size of the tank makes it even more appealing if you have little room under the sink. The air bladder comes pressurized at 8 psi and it can work with a feed water pressure of up to 100 psi.

You will notice no odd tastes or smells when using this tank because all the internal components are made of FDA-compliant materials. So no rubber or metal smell and taste or any contamination are going to happen.

The stainless steel shell is very robust and durable plus the 1/4” threaded connection is made of stainless steel too to prevent lead leaching. Unfortunately, like the iSpring T20M, this unit does not come with a tank valve as well, so you might have to use the old one or get a new one separately. All in all, if you want a smaller tank that can fit a constricted cabinet area, then the PA-E RO-122 is a good option.

The reverse osmosis storage tank is a very essential and necessary component in any RO system. Without an RO tank, it would probably take 5 to 10 minutes just to get a glass of purified water because the filtering process of most RO systems takes quite a bit of time.

A reverse osmosis tank, thereby, allows the system to maintain stable and constant water flow throughout. It makes the water supply quick, easier, and more controllable.

What is a reverse osmosis water storage tank?

Best reverse osmosis tank RO storage tank replacement

A reverse osmosis storage tank is a pressurized container within the RO system that’s used to hold the finished purified water after the filtration process through the RO membrane.

It holds the clean water until when you are ready to use it where the pressure inside the tank forces the water through the post-filter stage and then to the faucet.

A reverse osmosis tank basically has two main parts or rather storage bladders which are housed inside a shell made of either metal or plastic and separated by a high-grade butyl diaphragm.

The top bladder is the water chamber which is a virgin polypropylene liner that actually holds the filtered water. There is a water connection located on the top of the tank where water gets in and out.

The bottom storage bladder is the air bladder which contains the pressurized water and is also incorporated with an air charge valve located in the front or at the bottom of the tank.

Water accumulates in the RO tank and creates more like a “buffer storage” of pre-filtered water which helps ensure that there’s always a stable and constant supply of water for your immediate use.

How does it work?

Reverse Osmosis storage tanks utilize both water pressure and air pressure. As I mentioned earlier, the tanks are made up of two bladders, one at the top that’s filled with the clean water from the RO membrane and another at the bottom part that contains pressurized air.

The filtered water from the RO membrane is directed to the storage tank into the first bladder which is made of butyl with the top compartment consisting of virgin polypropylene which is a thick material much similar to the inside lining you see in a steel food can.

The purified water is pumped into this chamber until the pressure inside the tank reaches around 2/3 of the water inlet pressure from the RO membrane.

The flow of the filtered water into the bladder is cut off by the shut-off valve which also comes prepackaged with the tank. With the tank full of filtered water, the pressure inside it is much higher which in turn keeps the water pressurized too.

So, when there is a need for water and the faucet is opened, the pressure inside the air bladder pushes up the water out of the tank to the post-filter stage and ultimately to the point of use.

It’s the compressed air pressure inside the air bladder that pushes the filtered water out of the RO tank as soon as you open the faucet.

As the water is used and the levels in the tank drop, the pressure inside the tanks also reduces until a point where the shut-off valve disengages hence allowing more filtered water from the RO membrane to flow into the tank until it’s refilled.

This process is repeated several times as you keep opening the faucet to use the water. There’s always pressure inside the RO storage tank and water would flow into it only until the pressure inside it is about two-thirds of the pressure of the water inlet.

As I mentioned earlier, the water chamber consists of a butyl bladder which is a diaphragm that separates the air chamber from the water. Therefore, the water inside the storage tank doesn’t touch the metal or plastic material used in the tank.

It only contacts the butyl bladder which has been used for years in reverse osmosis storage tanks as it limits the growth of any germs and is regarded as inert.

The upper compartment of most modern metal RO storage tanks is also lined out with a virgin polypropylene material which is a plastic liner.

Therefore, the water never gets to touch the metal as it leaves or enters the tank which otherwise would lead to rust or a steel taste in the water that you drink.

Reverse osmosis storage tank Pressure

An RO tank always comes pre-charged with air. However, these pressure tanks are like tires, they need to be filled with air at some points as part of normal maintenance.

Generally though, when a reverse osmosis storage tank is empty with no water inside, the air pressure should be around 7 to 10 psi. The air pressure starts to increase though as the water is pushed into the butyl bladder.

Once the air pressure inside is about 2/3 of the incoming water pressure, the water flows into the tank stops. Therefore, if the pressure of the source water going into the RO system is 60 psi, then a full RO storage tank will have a pressure of about 40 psi.

To be accurate, the ideal air pressure in a full RO tank should be around 30 to 40 psi to ensure the system operates efficiently.

For optimal performance, the feed water pressure needs to be between 60 and 80 psi. Most RO systems though can operate correctly with pressure as low as 40 psi.

However, the lower the feed water pressure, then the lower the pressure inside the tank which also means the lower the amount of water in the tank. The result of this is a low flow of water at the RO faucet.

This can be remedied by enhancing the source water pressure using a boost pump. It’s designed to increase the water pressure, particularly for RO systems.

The higher the pressure, the faster and more water will be filtered by the RO membrane and be able to fill the tank properly.

RO Tank Capacity

The standard RO storage tank can hold a total of 2 to 5 gallons of water but the capacity can go up to 14 to 20 gallons. However, the stated capacity of RO tanks is usually more than if not twice the actual amount of water that will be held inside the tank.

This is because some of the capacity is taken up by both the air and the bladder. As such, a 4-gallon reverse osmosis storage tank may only hold approximately 2.5 gallons of purified water.

The reason why you don’t often get to notice when the amount of water in the RO tank is very little is that the system refills the tank each time you draw a glass of water.

Furthermore, if you need more capacity than what the standard tank holds, it is easier and even more economical to install a second small RO tank or replace the small tank with a larger one.

Metal RO storage tank vs plastic RO storage tank, which one is better?

Well, both tanks will give out the water of equal quality and have their advantages and disadvantages.

The main advantage of tanks with a metal shell is that they have a great pressure holding capacity compared to plastic tanks plus metal eliminates chances of air pressure loss except in case the bladder gets damaged after long use.

The advantage of plastic tanks, on the other hand, is that they don’t rust. However, they can be heavier and much costlier than metal tanks. Normally, the exterior of RO metal tanks won’t rust provided it’s kept dry.


Having a RO storage tank with good capacity and in good condition is necessary for ensuring that your RO system functions smoothly and delivers a consistent and fast water supply when needed.

If you are having issues with the capacity of your reverse osmosis storage tank or you are getting slow flow due to a damaged tank, then you might consider replacing your old tank with a new much better tank.

Our top ten list above should give you some insight into some of the best models you can find in the market including the things to keep an eye on.

Therefore, read all the detailed information we’ve provided above, then factor in your exact requirements, and hopefully you get to invest in the right tank that will suit you best.

RO Storage Tank Replacement

Time needed: 10 minutes

Reverse osmosis tanks may need to be replaced sometime when it breaks or starts to leak or the air bladder is unable to push the water out. The process is pretty easy and below are 11 steps you can follow to replace your RO tank.

  1. Turn off the feed water supply

  2. Start by turning off the feed water supply under the sink, then open the RO faucet and let it empty all the water it can.
  3. Remove the old tank

    The next thing is to remove the old tank by disconnecting the plastic hose which goes into the valve located on the top part of the tank.

  4. Drain out the remaining water

    With the tank removed, turn the valve on it and drain out as much water as possible into the sink.

  5. Remove the ball valve and tube

    Remove the ball valve plus the tube from the old tank in case you’ve not got a new valve for your new tank. Check if there’s any Teflon tape inside and gently remove it.

  6. Apply Teflon tape on the threads

    Now take the new tank and apply about 3 to 4 layers of Teflon tape on the threads of the outlet located at the top part.

  7. Tighten the ball valve

    Put the ball valve on while gently hand-tightening it. The plastic valve is very easy to crack, so it needs a little care here.

  8. Wrap the Teflon tape

    Wrap the Teflon tape clockwise to ensure that it tightens when you put the ball valve back on.

  9. Put the new tank in place

    Put your new tank in place and then reconnect the tube back in.

  10. Turn on the feed water supply valve

    Turn on the feed water supply valve while as well slowly turning the faucet on and checking for leaks as you go.

  11. Check for leaks

    In case there are no leaks, turn off the faucet and allow the RO system to run for around 20 to 30 minutes and then check again for leaks.

  12. Fill and drain the new tank before using

    Now once you are certain there are no leaks, let the tank fill with clean water and then turn on the faucet to empty all that water. Do this at least twice to ensure you get rid of impurities if there are any in the tank itself. That’s it.