Tankless vs Tank Reverse Osmosis System – Which Is Better?

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When selecting your RO system for the home, you will have the option of choosing between a system with a tank or one without.

Is one superior to the other?

Well, they are different for sure, and the choice should be made depending on your personal needs and preferences.

So, tankless vs tank reverse osmosis system – which is better for you?

Key Takeaways

  • There is no real difference in the ability of a tank or tankless reverse osmosis system when it comes to purifying water.
  • There are differences in size and functionality, though. While one type isn’t better than the other per se, there may be an option that works best for you and your needs.
  • Pros of a tankless RO system (with pump): Smaller, less wastewater, no secondary pollution, faster filtration, easier to install and maintain.
  • Cons of a tankless RO system (with pump): Usually more costly, requires electricity, often not customizable.
  • Pros of a tank-based reverse osmosis system (without pump): No pump noise, affordable, customizable.
  • Cons of a tank reverse osmosis filter (without pump): Larger, secondary pollution, more work required to clean tank and maintain pressure.

Tankless vs Tank Reverse Osmosis System – Which Is Better?

There are pros and cons to both kinds of systems.

For example, tankless reverse osmosis systems are much smaller if you have limited space.

Tank RO systems are usually cheaper and easier to customize if you are on a budget.

As they both operate slightly differently, knowing the differences between them may help you figure out which one is right for you.

As for now, you cannot really say that with tank is better than without or vice versa.

The Difference Between a Tank vs a Tankless RO System

What Is a Tank-Based Reverse Osmosis System and How Does It Work?

When RO systems first hit the market, they all came with a storage tank.

They are available in countertop and under-sink varieties, the latter of which usually has a 3.2-gallon metal canister that holds a pressurized rubber bladder made of butyl. This is where the water is stored.

The purpose of the storage tank is to store water for later use. RO is a slow process, filtering bit by bit. So rather than having you turn on the tap and your water coming out in drips, the idea of the storage tank was to allow plenty of water to be available that can be delivered quickly and at relatively high pressure.

Under Sink Reverse Osmosis System

The tank RO systems are triggered to filter water when levels begin to lower until the storage tank is full again – handy if your home water supply is cut for some reason.

The tank contains pressurized air and water, which helps send your water from tank to tap (often up the sink) without any pump needed. This maintains the line pressure in the system and stops water from being produced when the line pressure reaches a certain level, signaling that the tank is full.

Just like tankless systems, water will move through the pre-filtration stages before passing through the RO membrane and being stored in the tank, ready to use. The water will also usually flow through one or more post-filters before coming through the faucet.

What Is a Tankless Reverse Osmosis System and How Does It Work?

In more recent times, tankless RO systems have become very popular. They tend to be much smaller, sometimes ⅓ of the size of a tank system, and under sink units include a powered internal pump to create the pressure needed to push the water through the system at high speed and up to the faucet.

If the pump works effectively, you will have a steady flow of water on demand rather than having to rely on a storage tank being full.

Tankless countertop units may or may not have a pump, and this means the water will come out at a much slower pace.

Pros and Cons of a Tankless RO System

For the following pros and cons section, we are assuming that all tankless RO systems are using a booster pump.

Pro: Less Space Requirements

Tankless systems can be 50 to 75% smaller than their tanked-up rivals. If you are short on space or prefer the aesthetic of a more compact unit, then this would be a better choice.

Pro: Improved Recovery Rate

RO systems do tend to create a lot of wastewater, which is not much fun when it’s time to pay the water bill.

Tankless systems, which often come with a built-in pressure pump, have a considerably better pure-to-wastewater ratio, though, meaning fewer gallons of wastewater down the drain with these systems. The pressure pumps boost the internal water pressure in the system. This higher pressure means more water passes through the reverse osmosis membrane rather than escaping down the drain.

That said, a tank-based reverse osmosis system may also use a pump, but it’s much less common.

As such, a standard tank RO system can produce anywhere from 3 to 5 gallons of wastewater for every filtered gallon, but a decent tankless system (with pump) can get that down to as little as 0.25 gallons of wastewater per gallon of filtered.

Besides, an RO system using a pressure tank (bladder tank) creates backpressure. This pressure causes less water to enter the RO membrane, meaning more of the water going down the drain. This effect, however, is rather small.

Pro: Higher Contaminant Reduction Rates

The pressure pump in a tankless RO system also helps to increase the effectiveness of the RO membrane. This means the rate at which it filters contaminants will actually be higher, and the traces of contaminants in your water will be lower.

Pro: No Secondary Pollution

Secondary pollution can occur in tank systems as it is possible for contamination to occur while the filtered water sits in the storage tank – think plastic taste. Without a tank, there isn’t a possibility of secondary contamination occurring.

Pro: Fast Filtration

The internal booster pump makes sure that a tankless system filters water a higher rate of gallons per day than tank systems. For example: The AquaTru produces 1 gallon of clean water within 10-15 minutes.

Pro: Easier to Install

Tankless systems are often easier to install as there are fewer steps for installation. They also are much easier to handle without a large, cumbersome storage tank to navigate around.

Pro: Easier to Maintain

Tankless systems are easier to maintain. Monitoring storage tank pressure, a check valve, and an ASO valve doesn’t need to be done, and it is three less components to have to fix if things go wrong.

Con: Costly

Tankless systems usually come with a higher price tag. This is due to the built-in pumps.

Con: Electricity Required

Tankless systems need the pump to be operational, which does require electricity. Systems with tanks use air pressure rather than a pump, and even without electricity, you can utilize the water that is in the storage tank.

Con: No Purified Water During Blackout

If you live in an area with frequent blackouts, your RO system may not function at this time, as the pump will not be able to move water through the system. Keeping a container of purified water in your fridge for emergencies is an excellent idea in this case.

Con: Less Options for Customization

Due to the systems’ designs, you usually can’t add things like extra filtration steps, such as remineralization or UV disinfection.

Different Water Filter Cartridges and Membranes

Pros and Cons of a Tank RO System

We based the following pros and cons section on tank RO systems without pumps.

Pro: No Pump Noise

Tank systems do not contain a pump, so they are quieter than tankless systems.

Pro: More Affordable

Tank systems are, for the most part, more affordable than tankless. This is helpful if you are looking to install a reverse osmosis system on a budget.

Pro: Customizable

The systems are of a standard size and they can be customized most of the time. If a remineralization filter or an added UV light filter are musts for you, they can be incorporated into your tank RO system setup.

Con: Tank Requires Considerable Space

Due to the added storage tank, you will need at least double the space available to set this system up compared to a tankless system.

Con: Secondary Pollution

It is possible for bacteria to grow in the storage tank, re-contaminating your already filtered water. There are cleaning solutions available, but as you can’t see inside the tank, it’s hard to know what is going on in there.

There have also been complaints of the stored water tasting off, maybe due to the storage bladder materials leaching into the stored water over time.

Con: Hygiene

While you can clean the system with a sanitizing solution (be sure to unplug your ice maker and coffee machine first!), you cannot get into the storage tank to scrub it or to check that it has been adequately cleaned.

Con: Maintaining Tank Pressure

You need to check tank pressure once a year. This has to be done when the tank is empty. If pressure is low, you’ll have to increase it.

When to Buy a Tankless RO System?

When considering a tankless system, ask yourself

  • Is my water consumption high, and I don’t want to run out of water?
  • Does my plumbing have low water pressure?
  • Do I need a system that is easier to maintain?
  • Is creating less wastewater important to me?
  • Am I short on space?

Questioning what kind of features are important to you will help you make the right decision.

When to Buy a Reverse Osmosis System with Storage Tank?

If you are considering a reverse osmosis system with a storage tank, ask yourself;

  • Am I in need of a budget yet effective option?
  • Do I need to be able to customize with added filter steps?
  • Do I have an icemaker or coffee machine I need to connect to?
  • Do I have the space for it?
  • Can I install and maintain a more complicated system?

These questions should help you gain some clarity on if the storage tank option is the most suitable for you.

What to Consider When Buying

Your Home’s Water Quality

If your source water has a lot of sediment, or if it is hard water, or overly “dirty” for any other reason, you may need specific pre or post-filters for your RO system to work effectively.

It is essential to have your water tested to determine what kind of setup is best to prevent the RO system from being damaged.

Water Testing Report

NSF Testing/Certifications

Be sure to choose a unit with the appropriate NSF certifications if possible. These guarantee that you are purchasing a machine that will produce a gold standard of contaminant filtration and that the unit is made from high-quality materials.


RO removes all impurities from water, which includes minerals that are beneficial for our health. Remineralizing the water is possible with a post-filter that adds the good minerals back after filtration. This is particularly important if you are planning on using RO water for drinking long-term.

Feed Water Pressure

If you plan on using a system that does not come with a pressure pump, you must ensure that your feed water pressure is high enough. If it is too low, your RO system will create even more wastewater.

Clean to Wastewater Ratio

Each unit will be different regarding the clean water to wastewater ratio, so it is best to check with the manufacturer just how efficient your system is expected to be.

Filter Life

The life of your filters depends on water usage, but they do need to be regularly replaced, which does add to costs. Check with the manufacturer regarding your filters expected replacement times.

Available Space

Tankless countertop/under sink RO systems are usually smaller than their tank-based counterparts. So if you go with the latter, make sure you have then necessary space.

If you have any questions about tank vs tankless RO system please don’t hesitate to leave a comment below!

About the Author Alexandra Uta

Alex is a content writer with an affinity for research and a methodical attention to detail. Since 2020, she has fully immersed herself into the home water treatment industry only to become an expert herself. Alex has been using water filters and similar products for years which has gained her lots of hands-on experience.
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