An under-sink reverse osmosis system treats water slowly, so you need a storage tank that will collect purified water that is gradually treated. Without the tank, you can end up waiting a long time to fill a glass of water or a pot when you open the kitchen faucet. The tank collects water so you can have immediate access to treated water.
The reverse osmosis storage tank is designed to be stored under the sink in line with your under sink reverse osmosis system.
The storage tank is where filtered water is stored, waiting to be transported to its point of use. Storage tanks come in different sizes and this depends on the amount of water your family consumes.
Reverse osmosis tank comparisons
| Name | Image | Features | Where to buy | |
|---|---|---|---|---|
| 1 | Express Water RO132-TNK 4.0 gal Reverse Osmosis RO Water Storage Tank by TANKRO |  | Pre-pressurized / Pre-charged-7-10psi Capacity -4 gallons and 3.2 gallons RO processed water Connection - Water valve 1/4" at the top Certification -NSF certified Material -food-grade material-stainless steel, polypropylene, and butyl rubber Dimension-15x 11 x 11 inches Come with stand and tank ball valve | Check Amazon |
| 2 | iSpring T32M 3.2 Gallon Pressurized Storage Tank for Reverse Osmosis (RO) Systems |  | Pre-pressurized / Pre-charged-7-10psi Capacity -up to 3.2 gallons Connection - Water valve 1/4" at the top Certification -NSF/ANSI Standard. Material -food-grade steel, chlorobutyl diaphragm, and polypropylene liner Dimension-14 x 11 x 11 inches Come with a stand and tank valve | Check Amazon |
| 3 | PA-E Reverse Osmosis RO Water Storage Tank |  | Pre-pressurized / Pre-charged Capacity -6 gallons and holds 5.5 gallons of water Connection - Water valve 1/4" at the top Certification -NSF, IAMPO approved, and CE Material -food-grade steel, chlorobutyl diaphragm, and Virgin polypropylene liner Dimension-16 x 11 x 11 inches Come with stand and no tank valve | Check Amazon |
| 4 | APEC Water Systems TANK-4 4 Gallon Residential Pre-Pressurized Reverse Osmosis Water Storage Tank, White |  | Precharge/pre-pressurized-5-7Psi pressure of air Capacity -4 gallons and holds 3.2 gallons of water Connection - Water valve 1/4" at the top Certification - Dimension-14.5 x 11 x 11 inches come with a stand and no tank valve | Check Amazon |
| 5 | Watts Premier 119008 10-Gallon White Metal Pressure Storage Water Tank |  | Precharge/pre-pressurized-5-7Psi pressure of air Capacity -10 gallons Connection - Water valve 1/4" Certification - NSF tested and certified against ANSI/ NSF Standard 61 Dimension-23.5 x 16 x 16 inches come with a stand and no tank valve | Check Amazon |
| 6 | CrystalClear Reverse Osmosis Plastic Storage Tank |  | Precharge/pre-pressurized-5-7Psi pressure of air Capacity -4 gallons Connection - Water valve 1/4" Certification - NSF tested and certified Dimension-14 x 11 x 11 inches Inbuilt stand and no tank valve | Check Amazon |
How does a reverse osmosis tank work?
Most people ask themselves, as they physically look at the tank, if the way out is at the top, not at the bottom, as in many tanks. How does the tank deliver water right to your faucet or point of use?
Reverse osmosis tanks use air pressure to deliver water to the kitchen faucet. The air pressure helps deliver water without the use of a booster pump.
There are two pressure chambers inside the tank: one for air and one for water. The air pressure chamber is at the bottom, while the water chamber is at the top.
As purified water gets into the storage tank, the weight of the water will compress the air chamber. The more the air chamber compresses, the more it will continue to increase the pressure. When you open the faucet, the pressure will force water out of the tank and into the faucet.
If the tank did not have pressure, even if it was filled with water, it would not be capable of delivering water to the faucet unless you were using the delivery/demand pump.
So reverse osmosis tanks are special because they are pre-pressurized to provide water efficiently to the faucet.
If your tank that came with the RO system is not providing water and you have done troubleshooting you need to replace the tank by buying a new one.
That’s why we have provided a review of reverse osmosis storage tank replacement
Best Pressurized reverse osmosis storage tank in 2022
- Express Water RO132-TNK 4.0 gal Reverse Osmosis RO Water Storage Tank by TANKRO
- iSpring T32M 3.2 Gallon Pressurized Storage Tank for Reverse Osmosis (RO) Systems
- PA-E Reverse Osmosis RO Water Storage Tank
- APEC Water Systems TANK-4 4 Gallon Residential Pre-Pressurized Reverse Osmosis Water Storage Tank, White
- Watts Premier 119008 10-Gallon White Metal Pressure Storage Water Tank
- CrystalClear Reverse Osmosis Plastic Storage Tank
Pressurized RO storage tank reviews
Specification
- Pre-pressurized/Pre-charged-7-10 psi
- the capacity of 4 gallons and 3.2 gallons of RO processed water.
- Connection-Water valve 1/4″ at the top
- Certification-NSF certified
- material: food-grade material: stainless steel, polypropylene, and butyl rubber.
- Dimension-15x 11 x 11 inches.
- It comes with a stand and tank ball valve.
The tank pre-charge about 5-7 psi
Tankro tanks are manufactured using the finest FDA-approved materials such as stainless steel, polypropylene, and butyl rubber.
This tank has a capacity of 4 gallons and holds 3.2 gallons of on-demand filtered drinking water.
The water valve fits 1/4″ NPT and the air valve is made from durable brass for pressure adjustment. It comes with a tank ball valve.
When it comes to warranty the tank has a 1-year warranty and is NSF certified.
The tank is designed to fit under most kitchen sinks inside the cabinet and comes with a stand to secure the tank.
The tankRO reverse osmosis water storage pressure tank reservoirs are available in different capacities.
Specification
- Pre-pressurized/Pre-charged-7-10 psi
- It has a capacity of up to 3.2 gallons.
- Connection-Water valve 1/4″ at the top
- Certification-NSF/ANSI Standard.
- Material: food-grade steel, chlorobutyl diaphragm, and polypropylene liner.
- Dimensions: 14 x 11 x 11 inches.
- It comes with a stand and tank valve.
The tank size is 3.2 gallons and is designed for reverse osmosis applications.
To guarantee safety, the tank is constructed using stainless steel, food-grade materials, and FDA-compliant materials. The water chamber is made from a food-grade butyl diaphragm and a polypropylene coating to provide tasteless and odorless water.
It is done by an independent third party to meet the NSF/ANSI standard.
The tank is pre-pressurized between 7 and 10 psi for common use.
This tank discharges effectively in both vertical and horizontal positions.
The tank has a water valve that fits 1/4″ NPT and a standard air valve/nozzle for pressure adjustment.
The Ispring RO water storage tank is available in different capacities.
- 4-gallons (3.2-gallon holding capacity)
- 5.5 gallons-tank valve at the top
- 11 gallons-tank valve at the bottom
- 20 gallons-tank valve at the bottom
- 40 gallons-tank valve at the bottom
Specification
- Pre-pressurized/Pre-charged
- Its capacity is 6 gallons and it holds 5.5 gallons of water.
- Connection-Water valve 1/4″ at the top
- Certification -NSF, IAMPO approved, and CE
- Material: food-grade steel, chlorobutyl diaphragm, and virgin polypropylene liner.
- Dimensions: 16 x 11 x 11 inches.
- It comes with a stand and no tank valve.
To ensure you are consuming standard water, the tank is manufactured using FDA-compliant material and food-grade material. The water chamber is made with a high-grade chlorobutyl diaphragm and virgin polypropylene liner.
It is NSF approved under standards 58 and 61, IAMPO approved, and CE approved under the PED (pressure equipment directive).
The tank size is 6 gallons and holds 5.5 gallons of treated water.
This tank has a 1/4″ stainless steel water connection and a smooth internal air vent cap. It does not come with a tank ball valve.
It also features four nubbins that protrude at the bottom, which allows it to sit upright and level.
Cons
- No tank valve
PAE RO-132 RO pressure tank 4 gallon
Specification
- Precharge-5-7 psi pressure of air
- Its capacity is 4 gallons and holds 3.2 gallons of water.
- Connection-Water valve 1/4″ at the top
- Certification -NSF and CE
- Dimension: 15 x 12 x 12 inches
- It comes with a stand but no tank valve.
To make sure the tank is safe for human use, it is certified by NSF and CE. It is also made of an FDA-approved bladder, food-grade, with no rubber smell, no plastic smell, and a stainless steel connection on top.
The tank is 4 gallons and holds 3.2 gallons of water.
It is pre-charged with the 5-7 psi pressure of air.
This tank comes with a tank stand and the water inlet is 1/4″ NPT with stainless steel thread.
Cons
- No tank valve
PA-E RO-122 small Reverse Osmosis Water storage pressure tank
Specification
- Precharge-5-7 psi pressure of air
- Capacity: 3.2 gallons of water.
- Connection-Water valve 1/4″
- Certification-NSF Approved
- Dimensions: 14 x 9 x 9 inches.
- Material: food grade, post-cured diaphragm Virgin polypropylene liner
- It comes with a stand but no tank valve.
Specification
- Precharge/pre-pressurized (5-7 psi) pressure of air
- Its capacity is 4 gallons and holds 3.2 gallons of water.
- Connection-Water valve 1/4″ at the top
- Certification-
- Dimension-14.5 x 11 x 11 inches
- It comes with a stand but no tank valve.
The APEC water system’s 4-gallon pressurized tank holds 3.2 gallons of water.
The tank comes with a stand and you can easily position it vertically or horizontally.
It is made from food-grade polypropylene and butyl reservoirs. The quality of the material ensures tasteless, odorless, and contaminant-free water.
This tank has a 1/4 inch stainless steel connection and a sealed brass air valve. It is compatible with ¼ inch tank ball valve but does not come with it.
APEC water systems tank is available in different sizes
- APEC Water Systems TANK-20 20 Gallon
- APEC Water Systems TANK-14 14 Gallon
- APEC Water Systems TANK-3 3 Gallon
Specification
- Precharge/pre-pressurized (5-7 psi) pressure of air
- Capacity: 10 gallons
- Connection-Water valve 1/4″
- Certification-NSF tested and certified against ANSI/ NSF Standard 61.
- Dimensions: 23.5 x 16 x 16 inches
- It comes with a stand but no tank valve.
The Watts Premier Pressure Storage Water Tank is made from metal. Inside, the tank has a polypropylene liner and utilizes a butyl diaphragm for the water storage area.
It features a 1/4 in. male stainless steel connection, a Shrader valve for checking air pressure, and a tank stand.
This tank is NSF tested and certified against ANSI/NSF Standard 61.
Watts’ storage tank has a capacity of 10 gallons
Specification
- Precharge/pre-pressurized (5-7 psi) pressure of air
- Capacity: 4 gallons
- Connection-Water valve 1/4″
- Certification-NSF tested and certified
- Dimensions: 14 x 11 x 11 inches.
- It has an inbuilt stand but no tank valve.
The CrystalClear Reverse Osmosis Plastic Storage Tank is made from food-grade polypropylene.
The tank is NSF certified and has a 1-year warranty.
40 gallon reverse osmosis tank
40 gallon is a large reverse osmosis tank
TankRO – RO Water Filtration System Expansion Tank
Specification
- Pre-pressurized/Pre-charged
- Capacity: 40 gallons and up to 22 gallons of water for on-demand filtered drinking water.
- Connection-Water valve 1 “at the bottom
- Certification-NSF certified
- material: food-grade material: stainless steel, polypropylene, and butyl rubber.
- Dimensions: 38 x 18 x 18 inches
- It comes with a stand and tank ball valve.
iSpring T40M 40 Gallon Pre-Pressurized Tank for Reverse Osmosis (RO) Systems
Specification
- Pre-pressurized/Pre-charged
- Capacity: 40 gallons
- Connection
- Certification-meet NSF and ANSI Standards
- material: food-grade material: stainless steel, polypropylene, and butyl rubber.
- Dimensions: 41 x 17 x 17 inches
- The tank comes with a shut-off valve, tank connector, and tank stand.
What to consider when buying a reverse osmosis storage tank
- Capacity
Capacity is the amount of water the tank is capable of holding.
The storage tank comes in different sizes, measured in gallons. The size you require depends on your household usage. If you have a large family, you need a bigger tank for you to get enough water and vice versa.
In addition to the capacity of the storage tank, you should also know that the tank does not hold the amount of water the manufacturer says it does. If your tank is labelled “4.5 gallons,” remember that the tank has two chambers inside, one for air and the other for water. You will find that the tank will hold 3 gallons of water and the other part will be occupied by air. That is 70% water and 30% air.
4.5 gallons is the total amount of water the tank will hold without air, but if it is pre-pressurized, it will hold less.
- Material
A reverse osmosis tank should be made using quality materials. Make sure the tank or connections does not have material such as Lead, brass or copper. These materials were banned for use in purified/drinking water.
Material such as food-grade stainless steel and brass is okay. The chamber should be made from food-grade polypropylene and butyl reservoirs. Also, the quality of the material ensures tasteless, odorless, and contaminant-free water.
Can I increase the tank capacity with a second tank?
You can find the case where you bought a RO system with small tank storage capacities in such incidences you will receive less water required for your household.
You can increase the tank capacity by adding a second tank.
In these instances, you will find the tank getting less water than its capacity. You can increase the capacity by adding a booster tank.
This happens if the water supply has low pressure. More water will go to waste and less water will go through the reverse osmosis membrane, leading to less water going to the storage tank.
By increasing incoming water pressure, the tank will accumulate treated water faster.
How do I add pressure back to the tank if lost?
3-5 gallon tanks are recommended to have 7-10 psi. If the pressure is below 7 psi, you need to increase the pressure.
If the storage tank has lost its pressure, there is an air valve in the tank, mostly at the bottom part, that you can use to add pressure.
You can use a bicycle or electrical pump to add pressure to the tank.
How long does the storage tank last?
Most storage tanks last 10–15 years.
How do you know it’s time to replace the storage tank?
It’s not easy for you to know when it’s time to replace the storage tank, but some signs can tell you when it’s time to replace the tank. Such as
If you add pressure to the tank as described above and purified water fails to come out of the tank to the faucet, it’s time to replace the tank.
If the water comes out at the air valve, this means the bladder that divides the air and water chamber is damaged. There is no way to repair the bladder, which means the tank requires to be replaced.
FAQ
How to add a pressure tank using a bicycle pump
Open the cap covering the valve. Use a bicycle pump to add pressure. The standard pressure required for the majority of the tank is 7 PSI. You can use a pressure gauge to monitor pressure and not to over-or under-pressure. Add pressure until water starts coming out of the tank.
If you add more pressure than is required, which is above 7 psi, you will reduce the amount of water the tank will hold.
Reverse osmosis tank pressure
The standard pressure required for the majority of the tank is 7 PSI.
Reverse osmosis tank not filling up
In some instances, you will find the tank is not filling up.
If the tank is not filling up, it is mostly caused by feed water pressure (check the water pressure gauge to measure your incoming water pressure). If the feed water pressure is low, water is not capable of going through the RO membrane, leading to more water wastage. Therefore, the system produces less purified water to go to the storage tank.
If less water is purified, you will end up having your storage tank not filled with water.
To solve the problem, increase your incoming water pressure using a booster pump.
