Tankless vs. Tank Reverse Osmosis System

Reverse osmosis is one of the most powerful, effective, and popular methods of purifying water. The technology can remove almost all contaminants to give you pure and healthy drinking water.

There are 2 types of reverse osmosis water filtration systems that you can use in your home; one with a storage tank and one without.

The main difference between the 2 models is the number of RO membranes. While an RO system with a storage tank uses only one RO membrane, tankless models use multiple membranes to offer a more efficient filtration.

Is that all? Not exactly. In this post, we’ve compared the 2 models to help you settle for a suitable model. We’ve also included a list of the pros and cons of each model.

Quick Comparison Chart

FeatureTankless RO SystemRO System with a Tank
Water flow rateFast water flow rateSlow flow rate
MaintenanceEasy to maintainSlightly difficult to maintain
SizeSmall and space-savingTakes a lot of space
EfficiencyLess efficientHighly efficient
Secondary water pollutionNo secondary pollutionSecondary water pollution can occur in the tank

Tankless Reverse Osmosis System

Amazon’s Choice & with Alkaline Mineral

Perfect for Well Water

Tankless reverse osmosis systems are the latest additions (upgrades) to the different types of RO systems available today. And just like their name insinuates, these models don’t come with a storage tank.

The biggest selling point of tankless RO systems is that they save a lot of under-sink space. They also eliminate secondary pollution usually caused by the storage tank.

How Does It Work?

A tankless RO system, just like any other reverse osmosis system, removes sediment and salt from the water before forcing it through a semi-permeable membrane to eliminate dissolved solids.

After the water exits the RO membrane, it has to pass through a post-filter that polishes it before entering a dedicated faucet.

Different Reverse osmosis systems filter water in different stages depending on the number of pre-filters and post-filters.

When water enters a tankless RO system, it goes through pre-filtration. This stage usually includes a carbon and sediment filter. The 2 eliminate sediment and chlorine that could destroy the RO membrane.

Next, the water goes through the RO membrane, where dissolved solids are removed. After filtration, water comes out through the faucet when you turn it on.

One crucial factor to note is that since tankless RO systems don’t have storage tanks, they depend on the incoming water pressure for optimal operation.

They require water pressure values meaning that if the water pressure in your home isn’t high, the water production rate will be a disappointment.

You’ll have to get a booster pump to increase the water pressure to increase the flow rate.

Advantages and Disadvantages of Tankless RO systems


  • Occupy less space hence ideal for tiny kitchens
  • Deliver water instantly
  • Economical since it only delivers water when needed
  • Prevents secondary water pollution
  • Multiple membranes filter water more efficiently
  • Water has a better taste than that stored in a tank.


  • Come with a higher price tag
  • Depend on electricity to function
  • No water during emergencies
  • Replacement costs are higher than for systems with tanks

Reverse Osmosis Systems with Tanks

iSpring 100GPD 7-Stage with Alkaline Remineralization, Booster Pump & UV

Best for Well Water

Reverse osmosis systems with storage tanks use the pressurized tank to store the purified water until the demand is initiated.

The tank keeps the system efficient by turning the unit on and off.  As the tank fills with the RO water and pressure increases.

Tanked RO systems take a lot of under sink space and may not be ideal for persons with very tiny kitchen spaces.

Since reverse osmosis water filtration is very slow, the storage tank collects the water (gradually purified) so that when you pour yourself a cup of water, you get immediate access.

How Does Reverse Osmosis Systems with Tanks Work?

Reverse osmosis systems with tanks use pressurized tanks to store pure water until the demand arises.

The tank stores both water and air, which helps the system to deliver clean water fast and without a booster pump.

The storage tank has air and water chambers separated at the center by a bladder.

As the RO system feeds the water into the tank, the weight of the water compresses the air chamber. When the air compresses, it increases the pressure when you open the faucet.

The air pressure propels the RO water out of the tank and through the faucet into your glass.

In the context of an RO system, the storage tank performs 2 essential functions. First, it provides you with pressurized water when you need it.

Secondly, it maintains pressure throughout the system and actuates the on or off cycling of the system.

Advantages Disadvantages of Reverse Osmosis Systems with Tanks


  • More affordable than tankless models
  • Do not require a booster pump to operate effectively
  • More energy efficient
  • The stored water in the tanks comes in handy in emergencies


  • Take a lot of space
  • Have a slower water output
  • Can stem secondary pollution
  • Water doesn’t taste fresh


Reverse osmosis systems with tanks and tankless models all serve one purpose – supply you with purified water. And as you have already seen from our detailed comparison, each model has its pros and cons.

If planning to get a budget-friendly yet functional RO system for your household, purchasing a system with a tank would be an intelligent choice.

However, if you are short on space and interested in a system that is easy to maintain, get a tankless model.

Having said all that, the choice of system to go for solely depends on you. Now that you are well-informed, go for the RO system that suits your home best.

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