The Best Reverse Osmosis Expansion Tanks

Reverse Osmosis filtration systems produce clear, odorless, tasteless, and contaminant-free water.

5 Best-Selling Reverse Osmosis Expansion Tanks

One of the most important aspects of your Reverse Osmosis (RO) system is the expansion tank. Buying the right expansion tank is tricky, but our article will guide you to learn which tanks are best, how they operate to purify your water, and we’ll answer all your questions about buying the right tank.

An RO expansion tank is a pressurized storage tank for filtered and purified water. These tanks function by activating filtration through pressure that draws filtered water through the RO membrane and into the tank, and then out of its release valve.

Reviews of 5 Top Rated Reverse Osmosis Expansion Tanks

1. 4 Gallon Pressurized Water Storage Tank for RO Systems

ISpring T32M Pressurized Water 4 Gallon, 1/4" Tank Valve Included
Product Highlights:
  • metal pressurized tank with up to 3.2 gallon holding capacity
  • made from food grade butyl diaphragm with post-cure procedures provides a tasteless and odorless water chamber. tested by independent third-party to meet nsf/ansi standard
  • stainless steel 1/4" npt valve thread, 1/4-inch tank valve included
  • discharges effectively in both vertical and horizontal position
  • pre-pressurized between 7-10 psi for common use

This 4-gallon RO expansion tank holds 3.2 gallons of filtered water. They construct the tank of stainless steel with a food-grade butyl inner lining to hold water. With a pre-pressured 7-10 PSI, can easily be installed to your RO system as it has a maximum working pressure of 100 PSI. This particular tank can be used in both vertical and horizontal positions. Included in this package is a ball valve and tank stand.

2. 30 Gallon Reverse Osmosis Expansion Tank

TankRO RO Water Reverse Osmosis Water Storage Pressure Tank
Product Highlights:
  • reverse osmosis tank: made from 100% food grade materials, this ro water tank stores and keeps your water free from any contaminants and harsh chemicals. the perfect addition to any ro water system.
  • easy to install water tank: ro tank replacements for easy set-up
  • durable water storage tank: this ro water tank is rigorously tested for quality and durability and includes a 1-year warranty.
  • high quality water tank: this water storage tank is made from durable deep-drawn steel domes with precision welding to ensure long lasting value for your ro water system. coated with epoxy primer and polyurethane to even withstand the outdoors.
  • water tank dimensions: this large capacity water tank is 31 x 17.5 x 17.5 stores up to 18 gallons of water for on-demand filtered drinking water.

Constructed with deep-drawn steel domes precision welded and coated with epoxy primer and a polyurethane lining, this expansion tank can store your filtered water without contaminating it with chemicals or impurities. All materials used meet food-grade standards. This tank has a total volume of 30 gallons and can hold up to 18 gallons of purified water. They package it with a tank stand and a tank ball valve.

3. 14 Gallon Premium Pre-Pressurized RO Water Storage Tank

APEC Water Systems TANK14 Osmosis Water Storage Tank, White
Product Highlights:
  • pre-pressurized 14 gallon reverse osmosis ro water storage tank (holds up to 10.7 gallons of water
  • discharge efficiently in a vertical or horizontal position with tank stand
  • food grade bladder to ensure quality, safety and durability
  • upgrade for small 4 gal tanks- holds 3x more water with improved faucet delivery pressure
  • larger 3/4 inch male npt inlet/out connection for faster tank refills and flow rate

Holding 10.7 gallons of filtered RO water, this expansion tank’s materials comprise food-grade components to maintain the purity of the stored water. This tank can be used in both horizontal and vertical positions to suit any space for your RO system. The steel tank contains a polypropylene liner and a high-grade butyl diaphragm. With quick connectors, it allows for easy and fast installation to your RO setup. This unit does not come packaged with a ball valve nor tank stand; those are available separately.

4. 4.4 Gallon Stainless Steel RO Expansion Tank

44 Gallon Stainless Steel Osmosis Storage Tank
Product Highlights:
  • stainless steel ro reverse osmosis water storage tank
  • high quality 304 stainless steel construction
  • dual 0-ring air valve for "set and forget" operation
  • long life premium quality
  • no taste

Constructed with high-grade 304 stainless steel and precision welded, this tank offers long-life quality and durability. They fit it with dual O-ring air valves for easy DIY “set and forget” operation. The ball valve and tank stand are sold separately. Its air bladder is pre-pressured to 5-7 PSI. It also features a polypropylene inner lining that is food-grade certified to maintain the water’s filtered quality.

5. Vertical-Use 2.8 Gallon RO Expansion Tank

HIDROTEK 28 Gallon RO Systems -NSF Certificated-1/4"
Product Highlights:
  • smart size-2.8 gallon reverse osmosis ro water storage tank,size at 9.2 x 9.2 x 13.8 could be installed at any cabinet
  • material-stainless steel interface, 100% food grade polypropylene liner and butyl diaphragm,to ensure there are no chemicals in your drinking water
  • high quality-nsf approved food grade bladder to ensure quality, safety and durability,brand:hidrotek
  • inlet/outlet-stainless steel 1/4" npt valve thread ,tank ball valve is not included in the box, amazon asin :b078w6cfrh
  • application-designed for reverse osmosis water filtration system applications,pre-pressurized between 5-7 psi for common use

Using this 2.8 gallon expansion tank in your cabinet or under your sink, it must be positioned vertically for best performance. They construct it with a stainless-steel tank with a BPA-free and NSF-certified plastic inner tank for water storage. They make the air bladder of high-grade butyl. This tank also features an O-ring for leak-free seals. They do not include the ball valve and tank stand in this package; those items are sold separately.

Buying Guide

1. Food-Grade Materials

The components of your RO system must comprise food-grade materials. On the packaging or in the accompanying documentation, look for NSF (National Sanitation Foundation), ANSI (American National Standards Institute) or Food-Grade markings to ensure that the expansion tank won’t transmit any foreign objects or contaminants through your RO system. A food-grade expansion tank will keep your purified water free from any contaminants and harsh chemicals, ensure it is tasteless and odorless, perfect for consumption.

2. Durability

Of course, you want your RO system to last for many years. They commonly make expansion tanks of polyurethane or steel – with both types featuring butyl internal linings. Holding the RO filtered water, seals within the tank prevent oxidation and damage.

3. Air Bladder

Ensure your expansion tank has a reasonably sized air bladder. Despite the expansion tank able to hold a certain volume, the tank comprises an internal air bladder. This air bladder works to maintain the pressure in the RO system, enabling the pressure to draw water from the RO filter for storage. An air bladder 40% of the tank’s size will provide sufficient pressure to balance your RO system.

4. Maximum Working Pressure

While your RO system might have a pressure of only 40-80 PSI, your expansion tank needs to withstand higher pressures. Most good expansion tanks have a maximum working pressure of 100 PSI. Make sure your expansion tank is compatible with your RO filter’s needs.

5. Accessories

They usually sell expansion tanks with a tank ball valve and tank stand (for under-the-sink systems). With quick connectors, these are possible for home DIY installation.

Frequently Asked Questions

How long do RO expansion tanks last?

The tank itself will last for many years, but it is the membrane and lining inside the tanks that last about 5 years before needing replacement.

Why is my reverse osmosis tank not filling up?

The problem is most likely a fouled or clogged RO filter. Remove it for cleaning or replacement.

What pressure should my RO system be running?

A water pressure of around 60 PSI is ideal.

How do I know when my RO expansion tank is full?

You will tell when your RO expansion tank is full by releasing water from the faucet; if the system activates immediately, your tank is not full.

Why is water coming out slowly?

There is a clog in your system. Check your aerator for trapped air and a clog in your piping. It will reduce the system’s pressure to and from the expansion tank.


Making sure that your RO construct your expansion tank with the safest materials for food-grade standards will produce contaminant-free, tasteless, and odorless water. The expansion tank’s air bladder might be hidden from sight, but it serves to maintain the pressure in your RO system – and buying a tank with a strong air bladder will not only last longer but be able to draw filtered water into the tank more efficiently.