How Does a Reverse Osmosis Storage Tank Work?
Written by: Gene Fitzgerald // Last Updated: Mar 6, 2023
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Reverse osmosis systems are either tank-based or tankless units.
Needless to say, tankless RO systems have no tank, while tank-based systems use pressurized tanks.
If you’re wondering how such reverse osmosis storage tanks works, you’ve come to the right place!
Contents
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Key Takeaways
- A reverse osmosis storage tank is hydropneumatic and comprises two chambers separated by a plastic bladder.
- One chamber receives and stores purified water from the RO system.
- The other chamber contains air, which compresses and becomes pressurized as the quantity of water in the first chamber increases.
- On opening the RO faucet, the pressurized air pushes the filtered water out of the tank and up the sink.
- The compressed air also creates backpressure which shuts off the entire system once the storage tank is full.
What Is a Reverse Osmosis Storage Tank?
A reverse osmosis storage tank is a pressure tank that collects and keeps filtered water produced by a reverse osmosis system. It is hydropneumatic, meaning it holds both air and water under pressure.
Most RO storage tanks fit under the kitchen sink. They are made of steel or fiberglass, with their interior lined with butyl. The butyl lining prevents the steel from leaching into the RO water.
The Purpose of RO Tanks
The primary purpose of an RO storage tank is to readily provide purified water whenever you need it. The thing is, reverse osmosis is a slow process. It usually takes about five minutes to produce one glass of RO-purified water. RO tanks pre-store purified water, so you don’t have to wait five minutes before getting a single glass.
How Does a Reverse Osmosis Pressure Tank Work?
A reverse osmosis tank works by using air against water. Inside the tank, there’s a chamber for air and another for water. A butyl-lined “bladder” separates the two sections.
As the RO system filters water, the water chamber in the tank begins to fill. As the amount of water in the chamber increases, the air chamber compresses and becomes pressurized. So when you open your RO faucet, the already-tight air chamber releases pressure, pushing water out of the tank and up your sink.
Thanks to the air chamber within RO storage tanks, you do not need a booster or delivery pump for them to work.
Also, the compressed air bladder causes backpressure towards the reverse osmosis system. At a certain pressure level, when the tank is full, the system’s ASO valve closes and no more water gets purified. The water purification process starts anew as soon as you draw water from the RO faucet.
Further Reading:
The Benefits of Using a Reverse Osmosis Tank
Here’s what you’ll enjoy when you use an RO storage tank.
Stores Water for Later Use
The most obvious benefit of an RO tank is that it keeps water for future use. That way, you don’t need to wait to get purified water; it’s readily available!
You Have Purified Water at Hand Even During a Power Outage
If there’s a power outage, your remaining water pressure may not be enough to power your RO system. Booster pumps require electricity to work, so they won’t help either. In such cases, you can count on the purified water in your RO storage tank.
Bridging Distance to Fridges and Ice Makers
There’ll be pulse issues if your fridge or ice maker is far from a tankless RO system. That’s because you only have access to the quantity of water present in the waterline. If that water finishes, you must wait for the RO system to filter more water, which can be frustrating.
But with a large reverse osmosis tank, you can place your fridge up to 16 feet away and still get enough purified water from the fridge whenever you want.
Fast Water Output
Since there’s ready-made water, the system releases water quickly whenever you open the faucet.
Disadvantages
Reverse osmosis tanks have a few downsides as well that you must be aware of…
Requires Under Sink Space
You’ll need enough floor space (under or around your kitchen sink) to place a storage tank. If your kitchen area is cramped, you may be unable to use one.
Contamination
While it’s great that RO tanks store water for later use, there’s a chance that your purified water may get contaminated. If the water stays in the tank for a long time, microbes may grow, forming a biofilm in the tank. To avoid that, you need to sanitize your tank regularly.
More Wastewater
A tank will cause your reverse osmosis system to produce more wastewater than if it was tankless. That’s due to the backpressure created by the tank.
Capacity — How Much Water Does an RO Tank Hold?
RO tanks come in different sizes. The typical tank sizes are 2 gallons, 3 gallons, 4 gallons, 11 gallons, and 14 gallons.
However, these indicated sizes refer to the total volume of the tank, not how much water it can hold. This is because you have to deduct space for the bladder and air. So a 4-gallon tank, for example, would only hold around 2.5-3.2 gallons of water.
Can I Increase Tank Capacity Somehow?
Yes, you can. One way to do so is by adding a booster pump. Booster pumps increase the pressure at the feed, so your RO system can produce water faster. That way, your tank can hold more water before turning off.
The second way to increase tank capacity is to connect another storage tank to your existing one. That way, you can store double what your RO tank stores now.
How Long Does It Take for an RO Tank to Fill with Water?
Filling an RO tank with purified water takes two to four hours plus. It all depends on the tank size, water pressure, and your RO system’s flow rate.
What’s the Average RO Tank Lifespan?
Some experts say an average RO tank will last seven to ten years. Other experts estimate three to five years.
Truth is, your tank can last up to any number of years, depending on how you use and maintain it (think regular cleaning and part replacement).
Your water quality also affects your tank’s lifespan. For example, if the water is very acidic, the bladder in the tank will corrode more quickly. Then, there’s the quality of the tank itself. High-quality tanks will always last longer than cheap models.
How to Repressurize a Reverse Osmosis Tank
Sometimes, your RO tank may lose pressure and function slowly. If you have a bicycle pump or compressor, you can repressurize the tank by following these steps:
- Turn off the RO system’s water supply and the storage tank valve.
- Detach the storage tank from the system and move the tank outside.
- Turn on the tank valve to drain out water. Wait until the water stops rushing and only trickles.
- Grab a bicycle pump or compressor to pump air into the pressure valve. You’ll notice that a lot of water will come out of the tank.
- When all the water is out, use a pressure gauge to measure the pressure inside the tank. The goal is to raise the pressure to 6 to 8 psi, or the level stated on the tank label. So if it isn’t there yet, carefully pump air into the pressure valve again until it reaches the required level.
- Return the tank to its position, connect it to the RO system, and turn on the main and tank water valve. The tank will refill, and you can start using it as normal!
Why Do RO Tanks Loose Pressure?
It’s normal for RO tanks to lose pressure after some time. That’s because air will gradually move out as the storage tank operates. You’ll know your tank has lost pressure when it releases water slowly and the drain line runs constantly.
How and How Often to Sanitize a Reverse Osmosis Tank
To prevent microbial growth inside your reverse osmosis water storage tank, you should sanitize it once or twice a year. That’s also how often you’ll replace the filters, so it makes sense to sanitize the tank whenever you replace filters.
Now, to the how:
- Shut off the water supply.
- Flush as much water out of the tank as possible by opening the dispenser.
- Close the tank valve.
- Disconnect the tubing from the tank valve and drain any water inside of it.
- Use an eyedropper or similar tool to add a little bit of sanitizer like bleach or hydrogen peroxide into the tube.
- Reconnect the tubing.
- Open the tank valve.
- Turn the water supply back on.
- Allow water to run into the tank until full.
- Let the sanitizing solution sit in the tank for up to several hours.
- Drain the entire tank at least twice until all sanitizer scent has gone.
When Is It Time to Replace an RO Tank?
If your tank loses pressure regularly (like a few hours or days after repressurizing), it’s a sign that the bladder is damaged, and you need to replace it. Likewise, if your tank doesn’t release water after repressurizing, it’s time to replace it.
Tank vs. Tankless Systems
Let’s briefly compare tank-based with tankless reverse osmosis systems.
Tanks Are Quiet
Tankless systems need electricity to power the water pump, which can be pretty noisy. Tank-based systems, on the other hand, do not make noise because there’s no need to power a water pump.
Tank-Based Is Cheaper Than Tankless
Usually, reverse osmosis systems using a tank are more affordable at purchase.
Tank-Based Is More Customizable
Adding extra filters (like a remineralizer or UV purifier) to a tank-based system is easier most of the time. That’s because many tank-based reverse osmosis filters are standard-sized.
Tank-Based Is Slower When Empty
Tank-based systems usually release water fast, but if the tank runs out of water the system produces water really slowly which can be frustrating.
If you have any thoughts about the question, how does an RO pressure tank work, please don’t hesitate to leave a comment below!
About the Author Gene Fitzgerald
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