Top 10 Best Tankless Reverse Osmosis Systems | 2022 Reviews

Last Updated Jan 5, 2022
Disclosure: As an Amazon Associate I earn from qualifying purchases.

A tankless reverse osmosis system is the ultimate water purifier for your home. When you install this modern filtrations system, you get on-demand purified water much like a water fountain.

Standard under-sink reverse osmosis system owners often complain about how long it takes to fill a tank. Plus, a small tank might eventually need to be upgraded to a larger tank, which is a project in itself. Furthermore, a tank may require more room than you have, and it adds a point prone to contamination. To avoid these issues, simply choose the best tankless reverse osmosis system for your home.

In this article, I share reviews of the top tankless RO systems, the key specs to consider, and the pros & cons of ownership. Along the way, you’ll learn what to look for in a system to help you decide which one will serve your home, apartment, RV, and/or well water the best.

System Comparison

System Specs
#1) Waterdrop G3

  • Filters: 3
  • Capacity: 400 GPD
  • Model: WD-G3-W
  • Dimensions: 18.1″ x 5.7″ x 17.8″ (LxWxH)
  • Weight: 31 lbs
  • Warranty: 1-Year Limited
  • Price: $$$

#2) Frizzlife PD600

  • #1 Tankless Alkaline RO System
  • Filters: 3
  • Capacity: 600 GPD
  • Model: PD600
  • Dimensions: 14.7″ x 5.3″ x 15.5″ (LxWxH)
  • Weight: 28.9 lbs
  • Warranty: 1-Year
  • Price: $$

#3) Waterdrop G2P600

  • Filters: 2
  • Capacity: 600 GPD
  • Model: WD-G2P600-W
  • Dimensions: 17.32 x 5.91 x 13.9 (LxWxH)
  • Weight: 20.94 lbs
  • Warranty: 1-Year w/ Optional 1-Year Extension
  • Price: $$
#4) Greatwell RO System

  • Filters: 3
  • Capacity: 400 GPD
  • Model: ROG400
  • Dimensions: 11″ x 8″ x 15″ (LxWxH)
  • Weight: 19 lbs
  • Warranty: 1-Year Limited
  • Price: $$
#5) iSpring RCS5T Commercial Tankless RO Water Filter

  • #1 for Large Families & Light-Commercial Use
  • Filters: 5
  • Capacity: 500 GPD
  • Model: RCS5T
  • Dimensions: 14″ x 11″ x 17.5″ (LxWxH)
  • Weight: 32.7 lbs
  • Warranty: 1-Year
  • Price: $$$
#6) APEC RO-CTOP Countertop RO System

  • Filters: 4
  • Capacity: 90 GPD
  • Model: RO-CTOP
  • Dimensions: 14″ x 6″ x 6.5″ (LxWxH)
  • Weight: 7 lbs
  • Warranty: 1-Year
  • Price: $
#7) iSpring RO500

  • Filters: 3
  • Capacity: 500 GPD
  • Model: RO500
  • Dimensions: 17.4″ x 5.2″ x 16.25″ (LxWxH)
  • Weight: 21 lbs
  • Warranty: 1-Year Limited Manufacturer’s
  • Price: $$$
#8) Waterdrop WD-D6-B

  • Filters: 1
  • Capacity: 600 GPD
  • Model: WD-D6-B
  • Dimensions: 15.98″ x 5.98″ x 11.97″ (LxWxH)
  • Weight: 22.6 lbs
  • Warranty: 1-Year Limited
  • Price: $$
#9) Purlette Smart Tech
  • Filters: 2
  • Capacity: 400 GPD
  • Model: PL400G
  • Dimensions: 12.8″ x 7.5″ x 16.7″ (LxWxH)
  • Weight: 20.9 lbs
  • Warranty: 3-Year Manufacturer’s
  • Price: $$
#10) Waterdrop G2

  • #1 Budget System
  • Filters: 2
  • Capacity: 400 GPD
  • Model: WD-G2-B
  • Dimensions: 17.3″ x 5.9″ x13.9″ (LxWxH)
  • Weight: 20.9 lbs
  • Warranty: 1-Year w/ Optional 1-Year Extension
  • Price: $
#11) Waterdrop M5

  • New #1 Best Countertop Tankless RO System
  • Filters: 1 (5-Stage)
  • Operating Pressure Range: 29-87 PSI (No Electricity Required)
  • Filter Life: 550 Gallons
  • Model: WD-M5-G
  • Dimensions: 14.76″ x 8.35″ x 13.9″ (LxWxH)
  • Weight: 13.12 lbs
  • Warranty: 1-Year
  • Price: $

Top 10 Tankless Reverse Osmosis Systems

  1. Waterdrop G3 – 3-Stage – Under-Sink – 400 GPD – $$$
  2. Frizzlife PD600 – 3-Stage – Under-Sink – 600 GPD – $$
  3. Waterdrop G2P600 – 2-Stage – Under-Sink – 600 GPD – $$
  4. Greatwell ROG400 – 3-Stage – Under-Sink – 400 GPD – $$
  5. iSpring RCS5T – 5-Stage – Whole-House – 500 GPD – $$$
  6. APEC RO-CTOP – 4-Stage – Countertop – 90 GPD – $
  7. iSpring RO500 – 3-Stage – Under-Sink – 500 GPD – $$$
  8. Waterdrop D6 – 1-Stage – Under-Sink – 600 GPD – $$
  9. Purlette PL400G – 2-Stage – Under-Sink – 400 GPD – $$
  10. Waterdrop G2 – 2-Stage – Under-Sink – 400 GPD – $

Tankless Reverse Osmosis System Reviews

You’re probably wondering why the max capacity for tankless systems is so high? Standard under-sink RO water filters usually boast up to 100 GPD, and that’s considered a high-flow unit. Several of the systems in this guide offer 400 GPD or more. The most impressive of the bunch is the Frizzlife RO system with a whopping 600 GPD rating.

So what’s the deal?

The key is the extra-large RO membranes in these units. For example, the Waterdrop RO membrane is 15″ long and a whopping 4.3″ thick. That’s a lot bigger than a standard RO membrane and one of the main reasons this type of system can operate without a tank.

What impresses me the most is that the companies manage to fit a pump, membrane, and pre-filters into these compact units. As long as your incoming water pressure is in the 15 to 85 psi range, you’re good to go.

Additionally, these systems also manage to make less wastewater than traditional systems. This equals savings on your water bill and less guilt about dumping gallons of wastewater down the drain to make a single gallon of purified RO water.

Now that you have an understanding of how a tankless RO system works, let’s check out the individual reviews of each system to make sure you land on the right one for your home.

#1) Waterdrop WD-G3-W Reverse Osmosis Water Filtration System

As far as under-sink tankless RO systems go, the Waterdrop G3 is a bonafide trendsetter. Of the systems in this guide, the WD-G3-W has the most positive reviews to back up what it brings to the table. As I mentioned in the previous section, the RO membrane in this system is massive, which allows it to make up to 400 gallons of RO water daily on demand. No more waiting around for a tank to fill or worrying about low water pressure at your RO faucet.

What I really like about this system is almost zero chance of leaks. Traditional RO systems have tubing, more connections, and other points in the system that are prone to leaking. This system features a “smart leakage protector” that automatically cuts the water and power supply to the unit in the event of a leak. That’s just awesome.

The peace of mind you get knowing that you won’t need to fork out $1000s due to an RO system leak is an essential selling point. Believe me, I’ve seen more than enough horror stories about this happening, and unfortunately, there’s no 100% certainty that it won’t happen. With the WD-G3-W, you get the safest RO system on the market.

The internal smart water pressure pump ensures you always have optimal pressure and automatically adjusts according to your incoming water pressure. The built-in pump is a big reason why the unit sports a 1:1 filtered-to-wastewater ratio. Standard RO systems without pumps create as much as 5 gallons of wastewater to make just 1 gallon of filtered water.

Additional Highlights

  • An integrated TDS indicator that monitors filter performance
  • Automatic flushing to extend the life of the filters
  • Fewer filters to replace and maintain than traditional systems
  • Almost zero installation time
  • 0.0001μm filtration rating removes over 1,000 contaminants
  • Easy filter change system, replace filters in seconds
  • Space-saving at just 5.7″ wide
  • A smart lead-free faucet

Below are the pros and cons I found reported by owners in the Waterdrop WD-G3-W reviews:

  • The slimmest, most compact RO system on the market
  • Excellent customer service marks
  • The RO membrane is diesel, roughly 3X larger than a standard membrane
  • The filtered water tastes amazing
  • Changing filters is a breeze
  • Great water pressure at the faucet
  • Never run out of RO water
  • Installation is so much easier than installing a traditional under-sink RO system
  • Quiet operation
  • Requires electricty to function
  • Higher TDS readings than standard systems (15 – 40 ppm range)
  • You may not be a fan of the included faucet
  • Higher upfront cost than other Waterdrop systems

#2) Frizzlife PD600

The newly-crowned second unit of my best tankless reverse osmosis system picks is the PD600 by Frizzlife. The PD600 is one of the newest of the bunch, yet Frizzlife is a budget water filter brand I do trust. I put them in the same category as Waterdrop.

What makes the PD600 different from the Greatwell and Waterdrop systems? The main difference is the addition of a remineralization stage. If you’re a fan of drinking alkaline water or don’t like the taste of plain RO water, the PD600 is a better choice for you than the Greatwell and Waterdrop systems. Additionally, the PD600 has the highest max daily output capacity of 600 GPD, which is impressive, to say the least. You definitely won’t be waiting around at the sink to fill large pots and glasses.

You may also find that the water purification process is more powerful considering the rated contaminant removal rate of up to 99.99% of over 1,000 contaminants. The PD600 matches the 1.5:1 drain-to-purified water ratio of the Greatwell filter. Finally, if you enjoyed the TDS monitor in the Waterdrop system, the PD600 also features that touch. All in all, the PD600 is certainly worth a look, and it offers several features that other similar systems do not, including remineralization.

These are the pros and cons I discovered in the current Frizzlife PD600 reviews:

  • The convenience of an integrated remineralization filter means no fussy aftermarket installations and easy cartridge changes
  • Affordable replacement filters
  • Simple installation with minimal tools (takes about 30 minutes)
  • Low ppm readings after remineralization (below 20 ppm, and I really like this because some systems over-mineralize your filtered RO water)
  • You may find the outgoing water pressure is higher than Waterdrop (this is especially important if you feed the machine to an icemaker)
  • Quiet motor
  • Smaller than the Waterdrop WD-G3-W system for people short on under-sink space
  • Confirmed alkaline pH readings with a max of 9 (similar to bottled alkaline water pH levels)
  • Excellent taste reports
  • Impressively low wastewater production
  • The included faucet may feel somewhat flimsy
  • Currently priced higher than other systems in this guide
  • Made in China
  • You might not like the hum of the motor each time you dispense water
  • The faucet does not partially open to dispense water more slowly
  • Remember, it requires an outlet and will not work during a power outage like a traditional RO system (the APEC RO-CTOP does)

Watch the remineralization test below:

#3) Waterdrop G2P600

Convenience is the name of the game when it comes to Waterdrop’s latest G2P600, which is an upgrade over its popular G2 (WD-G2-W) system. When you first lay eyes on this system, you’re probably sold on the 2-filter design. It’s easier and more affordable to maintain, right?

Well, there are pros and cons to consider before choosing the WD-G2P600-W over the WD-G3-W, and the cons are the reason I rank this system after the WD-G3-W. As you already know, this system is more compact, easier to maintain, and costs a good chunk less than the WD-G3-W, at the time of this writing.

However, the cons to consider here are the composite filter and the lack of a post-carbon filter. If you have high TDS well water without pre-filtration, you’re going to run into problems having to replace the composite filter too often. Additionally, no post-carbon filer means the resulting water won’t taste as crisp as a system with a polishing (post-carbon)filter.

Overall, this system is best suited for renters and small households with less water demand. Be sure to consider these points before choosing the G2 series over the original WD-G3-W.

The following are the pros and cons I picked out from the Waterdrop G2P600 reviews:

  • One of the most compact systems on the market
  • Just 2 filters to replace, and since RO membranes have long lives, you really only need to worry about maintaining the composite filter
  • More affordable than other systems, better for folks on a budget
  • Higher output than the WD-G3-W (600 GPD vs 400 GPD), which means less waiting at the sink
  • An impressive 2:1 wastewater-to-pure water ratio
  • Easy installation with clear instructions
  • Low TDS reports of 20 ppm to below 10 ppm
  • Faster flow rate than the budget WD-G2-W system
  • Not the best choice for homeowners with high TDS water since the composite filter will have to do too much heavy lifting
  • No post-carbon filter for tastier water
  • The need to let the system run a bit between uses to avoid TDS spikes

#4) Greatwell ROG400

The Greatwell ROG400 system operates in a very similar fashion to Waterdrop units. A couple of key differences are the shape of the Greatwell system, and at the time of this writing, the ROG400 does cost less. What impresses me the most about this unit is the low wastewater production. According to Greatwell, this system produces just 1 gallon of wastewater for every 1.5 gallons of purified RO water. That’s easily one of the best ratios I’ve seen on the market.

As far as the specs, this unit also has the capacity to produce up to 400 gallons of RO water daily, it features 3-stage filtration with a large RO membrane, and it too removes up to 99% of over 1,000 water contaminants. It’s also important to consider that all quality RO systems remove up to 99% of contaminants as long as the semi-permeable RO membrane is doing its job.

One feature I like more in this unit than Waterdrop systems is the location of the tubing connections. Instead of in the back of the unit, the connections are at the top. Plus, there are individual filter life indicators for each of the 3 stages, which I think is pretty cool. One minor drawback is the filters aren’t quite as easy to replace in this system compared to the twist-and-lock Waterdrop design. One advantage of this system is it weighs less than most competing units, and it’s a few inches shorter.

These are the pros and cons I found reported by owners in the Greatwell reviews:

  • Installation takes just 30 minutes or less
  • You might find that the dimensions of this unit fit better under your sink than the longer Waterdrop WD-G3-W (it’s shorter)
  • The 400 GPD rating is for real
  • Lower TDS readings than the Waterdrop WD-G3-W (below 15ppm)
  • High customer service marks
  • Very pure-tasting water
  • Removes rotten egg odor due to hydrogen sulfide (good for well water)
  • No more chlorine taste or odor from municipal water
  • The pump might be noisier than you’d like
  • The instructions could be better
  • A TDS drop as the water exits the faucet, meaning the initial TDS is higher than after letting the water run a few seconds

#5) iSpring RCS5T Commercial Tankless RO System

The iSpring RCS5T is the most versatile system in this guide. Unlike the systems above, there’s the option to install this unit below your sink or customize it with your own tank. If you’re handy, it’s possible to convert it into a whole-house RO system that supplies all of your plumbing fixtures, including your shower. This installation does require a large holding tank and additional components, but bathing in reverse osmosis water is awesome nonetheless.

Since you’re here to find a tankless RO system, this system is excellent for under-sink usage. One qualm I have with the systems above is the handful of high resulting ppm reports.

iSpring is a company I trust to deliver an incredibly efficient RO membrane that’s going to give you purified water close to 0 ppm. The obvious drawback here is that this type of unit isn’t as convenient as the systems above. The installation process and filter changes are both more complicated. Personally, I don’t mind that and prefer this system over the two above, but you might prefer the convenience of the latest tankless RO design.

This beast of an RO filter removes up to 99.9% of contaminants, which is even more than the 99% offered by the Greatwell and Waterdrop filters. It also has a higher max daily output capacity of 500 GPD. The integrated booster pump allows for a 1:1 drain-to-purified water ratio, matching the Waterdrop WD-G3-W. Lastly, you may prefer the additional pre-filtration stages and the 5th stage post-carbon filter.

  • Low ppm readings of 10 or less (better than Waterdrop and Greatwell)
  • iSpring customer service is excellent
  • The system is well-built and designed for maximum efficiency by RO water pros
  • The option to convert it to a whole-house RO system
  • Exceptional-tasting water
  • Installation is easier than you might think
  • You may get more wastewater than advertised
  • It’s more than most small households need
  • No filter life indicators
  • A slight delay before the pump clicks on

#6) APEC RO-CTOP Countertop RO System

If you’re looking for a tankless portable RO system, this is the most reliable one on the market. APEC is a legit outfit that manufactures a wide range of RO systems, and they’re all some of the best-rated on the market. APEC designs, assembles, and engineers its systems in America, and most of its filter components are made in America.

The RO-CTOP is super compact, easy to install anywhere with a sink, and it’s the most ideal option for RV owners, renters who don’t want to modify existing plumbing, and anyone who wants a portable RO filter. The advantage here is no electricity is required. The main disadvantage is this unit does produce the most wastewater of the systems in this guide.

It’s a good idea to invest in a filtered water dispenser to get filtered water on demand since this system will take longer to fill a glass. However, that’s a small price to pay for the convenience of owning it. Compared to the other systems in this guide, the RO-CTOP cost less than half the price at the time of this writing.

Also, there’s an option to buy it with or without the case, and the model without the case is an absolute steal for the money. Finally, since there’s no reason to crawl beneath a sink to change the filters, changing the filters is quite easy.

  • There’s an option to convert it to an alkaline RO system with the addition of APEC’s food-grade calcium carbonate filter
  • APEC RO water is well-known for its superb taste
  • Super-low PPM readings down to 2, and they stay consistently low
  • Positive reports after years of daily use
  • No need to ever crawl under the sink
  • The most affordable tankless RO system in this guide
  • The slowest flow rate of the filters in this guide
  • Not as aesthetically pleasing to place on a countertop as an under-sink system
  • No filter life indicators
  • A handful of users ran into compatibility issues

#7) iSpring RO500

iSpring’s answer to Waterdrop’s WD-G3-W unit is its latest tankless RO500 system. Of the systems in this guide, the RO500 is the newest, and it’s just a bit smaller than the WD-G3-W. Keep this in mind if you prefer a shorter system because the PD600 and Greatwell are still the winners in the compactness department.

Next, it’s important to consider that iSpring is an established American-owned company with a longer history than Frizzlife and Waterdrop. I know some people are concerned about Frizzlife and Waterdrop manufacturing their systems in China. The good news is iSpring designs and assembles its systems in the US. However, it may import parts for the RO500 from China and/or Taiwan.

As far as specs, the first thing I like in this system is the first-stage 3-in-1 composite filter that captures all the larger sediment before the water enters the RO membrane. Next, this system delivers an impressive flow rate of up to .4 gallons per minute while keeping up with the trend of over 99% contaminant removal of over 1,000 contaminants. So, if you’re concerned about lead, fluoride, high chlorine levels, and more, this system gets the job done.

The final stage is a carbon block (polishing) filter to enhance the taste of your filtered RO water, which is nice to see. This undoubtedly makes for a tastier final product. Lastly, you get a smart faucet with real-time TDS monitoring and American-based support. Overall, this system is certainly worth your consideration if you’re already sold on the Waterdrop WD-G3-W.

The following are the pros & cons I found in the iSpring RO500 reviews:

  • Designed and assembled in the US unlike Waterdrop and Frizzlife
  • American-based support by a trustworthy American water filtration company
  • Backed by a 30-day money-back guarantee and 1-year warranty
  • Higher daily max output than the Waterdrop WD-G3-W and more compact
  • Fast .4 GPM flow rate (no waiting around to fill a glass or pot)
  • Real-time TDS monitoring at the faucet
  • The multifunctional composite filter is my favorite of the systems
  • Higher quality and more attractive faucet
  • Reliably-low TDS (reports below 10 ppm)
  • Filter status indicator
  • 2:1 wastewater ratio isn’t the best of the bunch
  • Pricier than other units in my guide
  • Instructions could be better

#8) Waterdrop WD-D6-B

Meet the latest addition to Waterdrop’s tankless RO series, the WD-D6-B or D6 system. At this point in time, Waterdrop is the undisputed leader in the tankless RO space. It’s clear that the Waterdrop team is working feverishly to advance its tankless RO technology and solidify its spot as the leader of the pack.

What’s the difference between the WD-D6-B and G3 & G2 systems? The biggest difference is the filter. This system requires just 1 filter to operate, though, it’s important to consider that the single filter does cost more. However, with proper maintenance, it only needs to be replaced annually. For folks with sediment in their water, it’s wise to install a point-of-entry sediment filter or other pre-filtration systems to extend the life of the WD-D6-B filter.

Outside of the single filter, you get 600 GPD capacity – to match the G2P600 – and the most compact size of the systems in this guide. All in all, this system is built with convenience and compactness in mind.

Lastly, I really like the attractive smart designer faucet included with this system. The faucet offers real-time TDS and filter life monitoring with a digital display.

Here are the pros & cons I found reported in the Waterdrop D6 reviews:

  • Only 1 filter to maintain is a serious advancement in tankless RO technology
  • Each filter features five stages of filtration with an integrated DOW RO membrane and post-activated carbon block layer for superior tasting water
  • The best faucet of the available Waterdrop models with real-time TDS monitoring
  • More compact than other Waterdrop models
  • 1.5:1 purified-to-wastewater ratio
  • Features a post-carbon filter while the G2 systems do not
  • Fast flow rate at 600 GPD
  • Good resulting TDS reports
  • Quiet 55 dB motor
  • Costly single replacement filter
  • People on well water or with high TDS water will most likely need pre-filtration to get the most out of the Waterdrop filter
  • Currently costs more than G2 systems
  • The filter slides out of the back of the unit unlike the front-loading G2 and G3 systems

#9) Purlette PL400G

Now for a change of pace. If you’re not a fan of Waterdrop, iSpring, or Frizzlife, the new Purlette tankless RO system is a solid alternative. It’s comparable to Waterdrop’s G2 series with its dual-filter system. The top-loading filter design is where you slide in the typical large RO membrane found in tankless systems and the Purlette composite filter. With this system, three filters last up to two years, which means you’ll change the composite filter annually and the RO membrane once every two years.

Three big selling points of this system are its WQA Gold Seal, a smart app with real-time alerts, and a long 3-year warranty. This is the only system with a smart app and a 3-year warranty in this guide. You might be thinking that the smart app is overkill, but it’s actually a nifty feature.

With the Purlette smart app, you get real-time TDS monitoring and precision filter life tracking on your iOS or Android device. Several final considerations are the shorter length of this unit compared to competing systems (though it is taller), integration with Alexa, an energy-saving auto-shutoff feature, and leak detection that automatically cuts off the water supply.

These are the pros & cons I found in the Purlette water filter reviews:

  • Authentic WQA Gold Seal water filter (direct link to official WQA page)
  • 3 filters last 2 years (2 composite filters and 1 RO membrane)
  • The only tankless system with a smart app that features real-time TDS and filter life monitoring
  • Compatible with Alexa and a member of Amazon Launchpad
  • Energy-saving mode
  • Automatic leak detection similar to the Waterdrop G3
  • 1.5:1 purified water to wastewater
  • Easy installation process
  • The 3-year warranty is longer than competitors
  • Taller than competing systems
  • Lower capacity at 400 GPD than similarly priced systems
  • Not recommended for use with water above 500 TDS without pre-filtration
  • Top-loading replacement filters rather than front-loading

#10) Waterdrop WD-G2-B

This guide wouldn’t be complete without Waterdrop’s best budget tankless reverse osmosis system. The clear advantage here is a significantly lower cost than the G3 system and the drop in price compared to model G2P600. Though, in my opinion, the price difference between the WD-G2-B and G2P600 models isn’t significant enough to sell me on this system over the more efficient G2P600.

So, with that thought in your mind, let’s quickly go over the key differences between the standard G2 vs the upgraded G2P600:

  • This system is rated 400 GPD while the G2P is 600 GPD
  • A wastewater ratio of 1:1 compared to the G2P’s more efficient 2:1
  • This system is available in black and white colors while the G2P is white only (if that’s important to you)

Comparatively, these systems are the same size and weight. Plus, they use the same replacement filters. The key takeaway is that the G2P is more efficient and gives you a faster flow rate.

All things considered, this is a great tankless RO system on a budget, just be sure to consider if the upgraded features in the G2P600 are worth the few extra bucks before choosing between the two systems.

Below are the pros & cons I discovered in the Waterdrop G2 reviews:

  • The front-loading filter design is the most convenient
  • Currently costs the least of the tankless Waterdrop RO systems
  • Uses the same filters as the G2P600
  • Filter life indicator on the tank
  • The same compact size as the G2P600
  • Excellent taste reports
  • Quiet operation
  • Easy installation with instructional videos
  • High-quality faucet for the price
  • 1:1 wastewater ratio isn’t the best of the bunch
  • 400 GPD means a slower flow rate than competing 600 GPD systems
  • You may notice TDS spikes that require allowing the system to run a bit before filling your glass

#11) Waterdrop M5 Tankless Countertop Reverse Osmosis System

For folks who aren’t fond of the countertop APEC system in this guide but desire a countertop system, the M5 is the perfect solution. Compared to the traditional appearance of the APEC RO-CTOP, the M5 is more modern. This means that it’ll look better in almost any kitchen. Plus, it’s even easier to use.

What are the main highlights of this system?

  • It’s non-electric which makes it extremely quiet (no pump sounds to worry about)
  • A true tankless countertop RO system with a built-in BPA-free 80 oz water pitcher
  • The single filter has a long life of up to 1 year or 550 gallons (the filter is the same type used in Waterdrop’s D6 system)
  • Detach the pitcher to store it in your fridge for cold water (similar to a water filter pitcher yet a whole lot better)
  • The filter features five layers of filtration including the RO membrane and a post-carbon layer

Now that you have an idea of what makes this system great and unique, let’s discuss a couple of drawbacks. When I first saw this system, I immediately thought it’d be perfect for renters. The problem is the installation. To install it, you must drill a hole in your countertop unless you already have an existing hole. Depending on whether you have an existing hole in your sink or counter, this could be the perfect system for you as a renter.

Secondly, there’s no built-in booster pump, so the pitcher takes 15 to 20 minutes to fill. If you want on-demand RO water for filling pots and other uses such as watering plants, this system doesn’t have the same high output level as the top systems in this guide. Overall, the M5 unit is the only one like it currently on the market and a great system for people who want something better than a water filter pitcher. Just be sure to consider the drawbacks before choosing it for your home.

These are the pros & cons I found reported in the Waterdrop M5 reviews:

  • The sleek design suits any kitchen
  • No electricity required is a big convenience
  • A lot quieter than other RO systems
  • Excellent water taste reports
  • A huge upgrade compared to Brita and PUR pitchers
  • More affordable than most systems
  • Straightforward installation with clear instructions
  • Long filter life and only 1 filter to replace
  • The detachable pitcher is great if you prefer to drink chilled water
  • You’re limited to 80 oz capacity per fill
  • 15-20 minute filling time per pitcher
  • May require modifications to install it (renters should be aware of this)

How to Choose a Tankless Reverse Osmosis System

The latest addition to this guide is this tips section to help you avoid common mistakes made by new tankless RO system owners. So, be sure to consider these points and come back later for more updates!

Tip #1 – Make Sure the System Has an RO Membrane

This might sound obvious, but I’ve noticed that some systems can deceive the untrained eye. For example, iSpring’s popular CU-A4 under-sink water filtration system is not a reverse osmosis system. Therefore, please do not choose this system because it does not use an RO membrane, nor is it an RO system. Having said that, it is a good home water filtration system, it’s just not reverse osmosis. The bottom line is that a system must have an RO membrane to be a tankless RO system.

Tip #2 – Beware of Fakes

As a continuation of rule #1 comes rule #2. To clarify, there are RO systems that appear to be tankless, however, they have internal reservoirs (tanks) and standard-size RO membranes. For example, the popular Broncell Circle system is not a tankless system. In fact, it uses an internal reservoir to hold water, hence why it doesn’t offer the same advantages as a true tankless reverse osmosis system.

Bottom Line

Now that you’ve learned how to choose the best tankless reverse osmosis system, I’m sure you know which unit is the right one for your home, RV, or apartment. It appears that tankless systems will slowly become the norm since most people want to save space, create less wastewater, and of course, perform less annual maintenance to get RO water on tap 24/7.

What impresses me the most about these systems is the 400+ GPD capacities and large RO membranes. The one drawback I did notice is the higher TDS readings compared to traditional RO filters. Depending on how much you value TDS, you might find that a traditional RO system is the better choice until the technology in these new tankless systems catches up.

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  1. I noticed you did not include a pros/cons list for the Frizzlife unit. Was that because is was added to your picks as an afterthought?

    • Greetings Michael, thank you for your feedback. To answer your question, the system was just about brand new when I wrote the article, and I didn’t have all the necessary information to put together a good list of pros & cons. I will update the article accordingly. As for Frizzlife, I trust the company’s products, and the PD600 is a good system for people who desire remineralization without making any modifications or purchasing additional parts.

      • Hi. Any update on Frizzlife? Their marketing materials have many misspelled words and their company history is all cliche. Makes me think a cheap Asian made device. Any input? Their specs true? Why only one machine adds minerals and alkaline back? Open to input.

        • Greetings Drew, in this price range, mostly all systems are made in China. Keep in mind, Frizzlife is a budget water filtration company that, in my opinion, offers some of the best water filters in its respective niche. As for the reason that it’s the only system with remineralization, a lot of companies are still catching up to offer true tankless systems. If you choose a different system, your best bet is to install an inline remineralization cartridge between your system and faucet below your sink.

      • Any chance you’ve gotten the pro/con list written and I’ve missed it?

        • Hello Tina, the article has now been updated to include the pros & cons for the PD600.

  2. Hello Kenny,
    By any chance you know that the Waterdrop and Frizzlife Tankless RO Systems are made here in the USA?

    • Hello Le Tran, Waterdrop and Frizzlife systems are not made in the US. Waterdrop claims to design its filters in the US and manufacture them in China aka the Apple approach. Frizzlife manufactures its systems in China and is headquartered in Denver, CO.

  3. Hello Kenny. About the Waterdrop G3 RO unit: I tested the TDS value of the water on the tap and it was well over 100 reading while the TDS indicator on the system read 22. After contacting Waterdrop I found out that in order to get water from the tap, at the actual reading on the indicator, I have to flush the unit for 1-2 minutes. So if I want a cup of water that is actually 22 ppm TDS from this system, I have to flush for about 1-2 minutes each time. Bottomline, the TDS indicator on the G3 unit reads deceptively low. The unit may be sleek and trendy but what matters is the quality of the water on demand at the tap. Had to return it.

    • Hey Juan, thank you for your input! I’m sure it will help others. Unfortunately, the need to flush any countertop or tankless unit is common to lower the TDS. The good thing is 100 ppm is still very low for drinking water. If you prefer drinking water below that level, you may want to consider installing a remineralization filter to replenish your water with essential minerals. Frizzlife’s system does this for you. Also, for your reference, the EPA recommends an upper limit of 500 mg/l which is 500.5711515 ppm.

  4. Could I use the Waterdrop WD-G3-W tankless system. I live on well water but I have a whole sediment filter down to 3 micron?

    • Hey Chris, as long as you have a sediment filter that’s removing any potential large sediment, there should be no issue. Problems only arise if large sediment reaches the 1st stage in the G3 system, which will shorten the life of the filter. If it’s convenient for you, you may also want to consider a multi-gradient sediment filter that goes down to 1 micron for added assurance and maximum filter life in the G3 system. Hope that helps!

  5. Thanks for a great review of the options. Couple questions for you:

    – In your review of the Waterdrop G3, you comment on the leak detection feature. Is this something that happens often? I’m new to reverse osmosis systems, so I don’t have any experience. If so, as you say, this could be a “dealmaker”
    – Have you looked at the NU Aqua Efficiency Series Tankless 600GPD Alkaline Remineralization Reverse Osmosis System? If so, any thoughts? On paper, it seems to have some nice features – tankless, 600 GPD, 2:1 pure to waste water, remineralization.


    • Greetings Stan, I’ll be happy to answer your questions:

      1) No, leaking is not common, and in most cases is due to user error than the system itself. Overall, this is a nice feature to have to protect your kitchen from flooding since we all know how much it costs to repair damage due to flooding.

      2) At first glance, the system by NU Aqua does appear to be legit. I like that the remineralization filter is similar to what’s offered in alkaline water filter pitchers and other similar products, though, some of the contents are somewhat iffy such as ORP balls. At the moment, I’d stick with what Frizzlife has to offer or adding a basic remineralization stage to a Waterdrop system.

      I hope that helps!

  6. Do all tankless RO systems require electricity? We do not have an electrical outlet under our sink however are looking for tankless options due to storage limitation in our under-sink cabinet

  7. Trying to decided on the iSpring RO500 versus the Waterdrop G3.

    I’ve read over 4 stages gets into diminishing returns. Is the RO500 considered a 5 stage since the first stage is a 3 in 1 filter?

    I currently have an iSpring 7 stage UV filter system ( on city water though) but it’s a pain to change the filters so looking at these newer systems and having a hard time choosing between two main options. Thanks!


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