Best Tankless Reverse Osmosis Systems of 2021

Best Tankless Reverse Osmosis Systems

If you get your tap water from a local supplier, you probably hope that your water is clean, safe, and healthy to drink.

But the problem is that water still contains contaminants in trace amounts. Even if water suppliers follow the EPA’s regulations and guidelines, ensuring that contaminants are filtered out to below their Maximum Contaminant Levels, many of these contaminants still have the potential to have harmful health effects.

Reverse osmosis (RO) is one of the most effective filtration methods available for removing these contaminants. If you’re inclined towards a tankless reverse osmosis filter in particular, I’m here to help you find a system that best suits your needs.

With a monthly readership of [monthlyreaders] and articles published in the likes of Sawyer Products and WQP Magazine, I’ve made it my business to be an expert on all aspects of water filtration.

By the end of this guide, you’ll know:

  • Which tankless reverse osmosis systems are best in 2021
  • The 6 things you need to consider before purchasing a tankless RO system
  • The advantages and disadvantages of owning a tankless reverse osmosis system

πŸ₯‡ Best Tankless Reverse Osmosis Systems

  • NU Aqua Efficiency Series Tankless Reverse Osmosis System
  • Waterdrop G3
  • Frizzlife Tankless Reverse Osmosis System
  • Waterdrop D6
NU Aqua Efficiency Series Tankless Reverse Osmosis System
NU Aqua Efficiency Series Tankless Reverse Osmosis System
Efficiency Ratio: 2:1
Filtration: 4 stages
Type: Standard, Tankless
Water Production (GPD): 600
Contaminants Removed: 99% of all contaminants
Waterdrop G3
Waterdrop G3
Efficiency Ratio: 1:1
Filtration: 7 stages
Type: Tankless
Water Production (GPD): 400
Contaminants Removed: 99% of all contaminants

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πŸ‘‰ Read the full review
Frizzlife Tankless Reverse Osmosis System
Frizzlife Tankless Reverse Osmosis System
Efficiency Ratio: 1.5:1
Filtration: 7 stages
Type: Tankless, Alkaline Remineralization
Water Production (GPD): 600
Contaminants Removed: 99% of all contaminants
Waterdrop D6
Waterdrop D6

Efficiency Ratio: 1.5:1
Filtration: 5 stages
Type: Tankless
Water Production (GPD): 600
Contaminants Removed: 99% of all contaminants

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⭐ Tankless Reverse Osmosis System Reviews 2021

NU Aqua Efficiency Series Tankless Reverse Osmosis System

NU Aqua Efficiency Series Tankless Reverse Osmosis System

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The NU Aqua Efficiency Series is a modern, compact tankless reverse osmosis system that hooks up to your kitchen faucet. With four stages of water purification removing up to 99% of contaminants in drinking water, the NU system is ideal for homeowners who truly care about their water quality.

Why It’s My Top Pick

  • More efficient performance; wastes only 1 gallon of water for every 2 gallons of pure water produced
  • 25% of the size of a traditional under-sink reverse osmosis water filtration system
  • Comes with a 120-day money-back satisfaction guarantee, so you’re not taking a risk when you buy this system
  • Easy to use and maintain, no tools required for filter changes.
  • Impressive 600 GPD (gallons per day) flow rate – there’s no waiting around for this system to filter your water.

This System’s Unique Features

The NU RO filter provides an efficient and effective water softening solution, with four stages of filtration that can remove a broad range of contaminants, including VOCs, chlorine, rust, and suspended sediment particles.

There are three filters in this system: a polypropylene/carbon block filter, which removes both sediment and chlorine tastes and odors; a granular activated carbon filter, which adsorbs chemicals and tastes; and the RO membrane itself, which removes salts, heavy metals, nitrate and more.

Changing the filters is easy in the NU Aqua Efficiency Series: just remove the front cover and twist the filters in and out of place. The PP/CB filter lasts up to 6 months, while the GAC filter lasts for 1 year, and the RO membrane lasts for 36 months.

Who It’s Best For

The NU Aqua Efficiency Series is best for people with a flexible budget, who are looking to save space and reduce water waste with a more compact, efficient reverse osmosis water filter.

πŸ‘ What I Like

  • Very efficient performance
  • 25% the size of a traditional RO system
  • Easy to change the filters

πŸ‘Ž What I Don’t Like

  • Quite expensive
  • Not NSF certified

Waterdrop G3

Waterdrop G3

At 5.68 inches wide, the Waterdrop G3 is a slim, space-saving reverse osmosis water filtration system that’s ideal for installing in under-sink locations with limited space. This system is NSF 58 & 372 certified for quality of build and lead reduction.

Why It’s a Top Pick

  • Comes with a smart faucet & filter change light, so you know exactly when to replace the filters
  • Only 5.68 inches wide, ideal for space saving underneath a countertop or kitchen sink
  • Has two official NSF certifications – Standards 58 and 372
  • Smart TDS monitoring panel lets you know that the system is working
  • Offers a 400 GPD fast water flow, so there’s no waiting around for filtered water
  • Takes under 30 minutes to install, and filter replacements take minutes

System Features & Benefits

The Waterdrop G3 is one of the smartest tankless RO systems available, with so many clever, handy features that make it a top pick in this guide.

The unit comes with its own dedicated faucet, which has a filter change light and a sound reminder to indicate when you’ll need to replace your filters. There’s also a smart TDS monitoring panel that tells you how many TDS have been removed from your water, letting you know that the filters are properly doing their job.

There are three filter stages in the G3: a PP cotton and carbon block filter, which removes sediment, chlorine and lead; an RO filter, which removes TDS, and a post-activated carbon filter, which removes any lingering contaminants.

The G3 is easy to install yourself, and takes less than 30 minutes. You can put the system into holiday mode when you’re away, so you don’t have to worry about issues with the filters during this time. The unit has a 1:1 wastewater to pure water production, making it far more energy-saving than most RO systems.

Who It’s Best For

If you’re a fan of smart, handy features and add-ons, you’ll love the Waterdrop G3. This system is ideal for you if you think you might forget to change the filters or you don’t want to buy your own TDS meter to check that the unit is working.

πŸ‘ What I Like

  • Comes with a host of smart features
  • Fast water flow
  • Quick, easy installation

πŸ‘Ž What I Don’t Like

  • Doesn’t remineralize water
  • At the top of the tankless RO price range

Read Full Review: Waterdrop RO WD-G3-W Reverse Osmosis System Review (2021)

Frizzlife Tankless Reverse Osmosis System

Frizzlife Tankless Reverse Osmosis System

The Frizzlife Tankless Reverse Osmosis System is a three-stage no-tank reverse osmosis filter that removes TDS and alkalizes water. This unit has an impressively high flow rate of 600 GPD and offers an efficient performance, with a drain ratio of 1.5:1.

Why It’s a Top Pick

  • It’s one of the few RO systems with a built-in alkalizing filter for increasing pH
  • Removes more than 1,000 contaminants
  • Saves up to 60% space with its compact, tankless design
  • Very fast performance – takes just 8 seconds to fill a 250ml glass of water
  • Easy to install and replace the filters; avoid guesswork with the filter change reminder

System Features & Benefits

The Frizzlife Tankless RO System uses 7 deep filtration processes within a sediment filter, a carbon block filter, an RO membrane, a remineralization filter and a weak alkaline filter, resulting in almost 100% TDS-free, alkalized water.

This advanced tankless unit removes a broad range of contaminants, including chlorine and chloramine, lead, chromium, fluoride, arsenic, organic and inorganic pollutants, cysts, and aluminum.

The Frizzlife has a super-low drain ratio, helping you save up to 450% compared to a traditional under-sink reverse osmosis system. It’s also much easier to install, and changing the filters is as simple as twisting the old filter out and clicking the new filter into place.

A big benefit of this unit is that it reintroduces essential minerals into your water and increases its pH, improving its health properties.

Who It’s Best For

If you’re keen to use a reverse osmosis filter that you don’t have to wait around for, the Frizzlife Tankless RO System is the answer. This filter offers an impressive 600 gallons-per-day flow rate, and takes just 8 seconds to provide enough water for a 250ml cup.

πŸ‘ What I Like

  • Remineralizes water
  • Fast flow rate of 600 GPD
  • Efficient, water-saving performance

πŸ‘Ž What I Don’t Like

  • Included faucet is a little flimsy
  • Made in China

Waterdrop D6

Waterdrop D6

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The Waterdrop D6 is another no-tank reverse osmosis drinking water unit offered by Waterdrop. This system has a daily flow rate of 600 gallons and uses an all-in-one filter to remove up to 99.99% contaminants.

Why It’s a Top Pick

  • Sleek, black design that would fit well in a modern kitchen
  • Impressive drain ratio of 1.5 gallons pure water to 1 gallon wastewater
  • Uses just a single filter that offers a 5-in-1 performance, requiring less upkeep
  • Smart faucet shows a real-time TDS level and remaining filter life
  • Provides up to 600 gallons of water a day

System Features & Benefits

With its attractive black design and 5-in-1 performance, the Waterdrop D6 is an RO filter system that looks good and offers a high performance.

This RO drinking water filtration system removes up to 99.99% impurities, including chlorine, lead, salt, nitrates, chromium, and more. The system combines two cotton polypropylene layers, an activated carbon block layer, a reverse osmosis membrane layer and a post-activated carbon block layer within a single filter cartridge.

Offering up to 600 gallons of water per day, this RO system should meet your entire family’s drinking water needs. It’s easy to install, and the filter cartridge has a decent filter life of 1 year, so your maintenance duties are minimal.

The main difference between the D6 and the G3 is that the D6 is slightly more compact and convenient, as it uses just a single filter. The unit also has a faster flow rate of 600 GPD, but a more impressive wastewater to pure water ratio of 1.5:1. Having a single filter cartridge is what makes this system more affordable upfront.

Who It’s Best For

The Waterdrop D6 is ideal for people looking for convenience. It also has one of the most attractive designs for an RO system, and is ideal for installing in a modern kitchen.

πŸ‘ What I Like

  • Only 1 filter to maintain
  • Attractive design
  • Impressive 600 GPD flow rate

πŸ‘Ž What I Don’t Like

  • Quite noisy when in use
  • Filter costs a lot to replace

🧾 Tankless Reverse Osmosis System Buyer’s Guide

If you’re looking to learn more about tankless RO systems before you decide whether they’re right for you, I’ve covered everything you need to know in the buyer’s guide below.

πŸ€” What is a Tankless Reverse Osmosis System?

A tankless reverse osmosis unit is just like a standard reverse osmosis system, except it doesn’t use a tank.

Traditional reverse osmosis systems store filtered water in a tank before use. This means that you get instant access to filtered water when you turn on the tap, rather than having to wait for the water to pass through the RO system before it’s ready to drink.

Tankless RO systems don’t have a tank, but that doesn’t mean they offer a slow performance. Many tankless RO units are fast-performing, taking less than 10 seconds to fill a glass with water – and, of course, their tankless design makes them much more space-saving.

βš™οΈ How Does A Tankless RO System Work?

In a tankless RO system, the entire RO process is the same. The only real difference is that, instead of entering a tank after it has been filtered, water is filtered on-demand, and passes straight through the system and out of the faucet.

Usually, this type of reverse osmosis water filtration system features a minimum of three filter stages: a sediment pre-filter, an activated carbon or carbon block filter, and a semi-permeable RO membrane. Some RO filters also come with a post-filter that removes lingering contaminants, or a remineralization filter that reintroduces healthy minerals to water and increases its alkalinity.

A high pressure is required to send water through each filter stage with enough force. The pre-filter removes suspended solids, while the carbon filter removes chemicals like chlorine and pesticides, and the RO membrane removes the majority of total dissolved solids (TDS).

Tankless RO System Stages
Tankless RO System Stages

The semi-permeable membrane features tiny pores, usually 0.0001 microns or smaller, which act as a barrier to the majority of contaminants. These impurities end up bouncing back into the RO chamber, where they are washed away with a small amount of wastewater.

Next comes the post-filter and/or the mineral filter, if the system has one. Once water has made it through these stages, it will be sent straight out of the system’s dedicated faucet, ready for drinking.

πŸ‘ Advantages of Tankless Systems

Some advantages of tankless reverse osmosis systems are:

Space-Saving Design

If you’re short on space, a tankless RO water filtration system is the obvious choice. With no storage tank to take up valuable room underneath your counter or kitchen sink, most tankless systems are slim enough to store in the corner of a cupboard without dominating space.

On-Demand Water Filtration

RO systems with a water storage tank have to use an extra filter to remove any bacteria or microbiological contaminants that might have collected in the water while it was stored in the tank. There’s no danger of this contamination with a tankless RO system, as it provides instant, on-demand water filtration.

Fewer Individual Filter Changes

Because tankless RO units have compact, space-saving designs, they often contain fewer filter cartridges, or merge several filter stages within a single cartridge. This means you have fewer individual filters to change, which is a bonus if you’re looking for minimal maintenance.

More Economical

Tank-based reverse osmosis water filtration units produce a constant supply of water to ensure the storage tank is always filled. Tankless units are more economical, as they only produce water when it is actually needed.

Improved Water Taste

Water that has been sitting in a storage tank doesn’t taste as nice as water that has been delivered straight from a smart faucet. Tankless water filters provide fresh drinking water whenever you need it.

Better Smart Features

I’ve noticed that the tankless RO water filters that are currently available offer a range of smart features that not many tank-based systems offer. A smart faucet with a filter indicator light is very handy, as is a built-in TDS reader.

Easier to Install & Maintain

Because they only consist of a single unit, tankless RO water filters tend to be easy to install, taking less than half an hour. While you might have to pay for a plumber to install a whole-home or under-sink tank-based system, most tankless designs are simple enough for DIY installation.

Changing the filters is also much easier in most tankless systems. You simply open the unit and take out the old filter, replacing it with a new one.

πŸ‘Ž Disadvantages of Tankless Systems

There are several disadvantages of tankless RO water filtration systems that are worth being aware of:

More Expensive

Because of their space-saving, on-demand water benefits, tankless RO water filters are typically more expensive than tank-based options. You should prepare to pay at least $450 for one of these water filtration systems. Some can even cost as much as $600.

Still Quite Inefficient

While tankless RO water filters are designed to be more efficient and less wasteful, they do still waste water compared to other water filtration methods. This may bother you if you don’t want the extra cost of using water that you don’t actually get to drink.

May Take Slightly Longer to Deliver Water

I’ve mentioned that tankless reverse osmosis units are quick to deliver filtered water, but they still have to send water through every single RO filtration stage before it can leave the smart faucet. This means you’ll probably have to wait several seconds longer for water from this system than you would from a system with a tank.

No Water Storage in Emergencies

The one advantage of a tank-based RO system is that it will provide access to a batch of clean, filtered water if an emergency occurs and your water supply line is cut off. A tankless unit can only produce water when you turn on your faucet, so it doesn’t offer this benefit.

πŸ’­ Considerations When Buying a Tankless RO Filter

Before you buy a tankless reverse osmosis water filtration system, consider the following things:

Incoming Source Water

Your incoming water source is not such an important factor with a reverse osmosis unit, as most RO water filtration systems are capable of removing more than 99.9% of all TDS in water anyway.

Total dissolved fluids (TDS) Chart

However, if you do have an idea of the specific problem contaminants you’d like to remove, it will help you to make a decision on the right RO water filter system for you based on what contaminants a filter is advertised to remove.

I recommend testing your water to determine which impurities are present in the highest concentrations before you buy an RO system.

Water Pressure

Your incoming water pressure is less of an issue with most tankless reverse osmosis water systems than it would be for a whole-house system.

Most reverse osmosis drinking water filtration units just require that your ongoing water pressure is in the 15 to 85 psi range.

However, if your water pressure is on the lower end of this range, you might find that water’s flow rate through your RO water filter is slower, especially at the reverse osmosis membrane. The system may waste more water than necessary, and produce a slower stream of water.

Fixing low water pressure is relatively easy: just buy a booster pump. A booster pump can increase your water pressure to a consistent rate, enabling your RO system to perform faster.

You can sometimes buy a booster pump as an add-on to your initial RO purification system purchase. Otherwise, they’re available on most online marketplaces.

Water Pressure

Produced to Wastewater Ratio

Tankless versions of RO units have a better pure water to waste water ratio than traditional under-sink models.

A tankless purification system may only produce up to 1 gallon of waste water for 1 – 1.5 gallons of pure water produced. The better this ratio, the less tap water you’ll waste per day, and the more money you’ll save.

Flow Rate

Flow rate ties into water pressure somewhat, but an RO water system itself may purify your tap water at its own measured flow rate, regardless of your water pressure, depending on its design.

It’s essential that an RO system has a good sediment filter that can remove large particles that will block later filtration stages, slowing down the flow of tap water.

Flow rate will also naturally slow down as the filters get closer toward the end of their lifespans. At their peak, RO systems should offer a water flow of 400 gallons per day. Some systems even offer a flow of up to 600 gallons per day.

Flow Rate

Remineralization Needs

Reverse osmosis water filtration systems are highly effective, removing almost every single impurity your water contains. The problem with this is that the beneficial impurities, such as healthy minerals, are also removed.

An increasing number of tankless reverse osmosis units are now offering remineralization filter stages, which add minerals back into water and increase its alkalinity. The benefit of this is that you get to enjoy pure, clean drinking water that still contains healthy minerals, and tastes better because of it.

Remineralization isn’t essential, so it’s worth considering whether you’re interested in this filter stage before you decide on a tankless water filtration system. Your choices will be more limited if you want a system with a built-in remineralization stage, and the system will probably cost more, too.

Alternatively, you could choose to remineralize your water with mineral drops before drinking, which means you’ll still get the broader choice of RO filter systems.

Filter Lifespan

Tankless reverse osmosis drinking water systems tend to use the same types of filters as traditional under-sink systems, so you can expect filter life to be largely the same, too.

The filter life of a semi-permeable membrane is usually around 2 years. RO carbon filters have a filter life of about 12 months, and pre-filters usually have a 6-9 month lifespan.

Space Available for Installation

Probably your biggest incentive for buying an RO system without a tank is its space-saving benefits. But not all tankless RO units save the same amount of space.

It’s important to measure out your available space carefully and compare this to the measurements of a unit you’re interested in. While most units are slim, some might be too tall for your cupboard or under-sink space.

If you want to save the unnecessary hassle of returning a system that doesn’t fit in your available space, do the measurements before you buy anything.


Like most drinking water filters in the US, manufacturers of reverse osmosis systems can apply to be tested and certified by NSF International, an independent body that tests, inspects and certifies food and water consumer products.

nsf logo

There are several NSF certifications that an RO system can obtain:

NSF 58

NSF 58 is the certification dedicated to reverse osmosis systems. If a system has an NSF 58 certification, it means that it offers a high level of performance expected from an RO unit, and can remove total dissolved solids to its advertised level.

NSF 53

It’s common for reverse osmosis systems to be certified to NSF 53, too, for the removal of heavy metals like lead, arsenic, and mercury.

NSF 372

NSF 372 is a certification that manufacturers can obtain if they prove that their system meets standards for lead compliance (i.e. that it isn’t made from components that will leach lead into water).

πŸ”§ Tankless Reverse Osmosis Water Filter Maintenance

Tankless reverse osmosis units are relatively low-maintenance. All you’ll need to do is replace the filters, and this is easier to do than with a traditional under-sink system.

The exact RO system you buy will determine how often you need to replace the filters. Some systems may also have more filters than others; for instance, one system may have a single all-in-one filter that only needs to be changed once a year, while another has three separate filters and a remineralization filter that each have their own lifespans.

Tankless Reverse Osmosis Water Filter Installation and Maintenance

You should expect to have to replace your filters at least once a year, so make sure you’re happy and committed to this maintenance task before you make a purchase.

Your water usage will also have an effect on how often you need to replace the filters in your RO system. The bigger your family, or the more water you use, the faster the filters will become clogged and wear out.

On the other hand, if you’re in a single-person household and you only use your water in the early mornings and evenings, you may get much longer out of your filters than advertised.

If you’re not sure you’ll remember to change your filter, I recommend buying an RO system with a built-in filter life indicator. This will change color to let you know when your filter needs to be changed.

❔ Frequently Asked Questions

Can I get a tankless reverse osmosis water system for my whole house?

I haven’t come across any tankless whole-house reverse osmosis systems just yet. Most whole-house units have very large tanks for water storage. You may have issues with providing your entire home with enough tap water from a whole-house tankless model.