The 9 Best Tankless Reverse Osmosis Systems for Super-Clean Drinking Water

By: Jake Gallagher | September 27, 2023

If there were a celebrity among water filters, it would be the reverse osmosis system. These filters are the most efficient when it comes to cleaning contaminated water.

As technology has advanced, new tankless reverse osmosis systems are dominating the market, and rightly so. They provide healthy drinking water without occupying as much space as traditional tank systems, as well as reportedly wasting less water, making them an eco-friendly option. 

But tankless systems also have some downsides, like poor flow rate, drain ratio, and filter quality, not to mention the false claims some brands make for their products to stand out. 

I’ve gone through the trouble of finding the best tankless reverse osmosis system for clean water based on authentic research and reviews. 

Let’s dive into it. 

1. Waterdrop G3P600: 9.70/10 

  • Unbeatable filtering ability 
  • $599

Waterdrop is a European brand that excels in tankless water filtration systems. It’s my number one recommendation because it uses eight stages of filtration to filter the most contaminants from your water. 


The concept of reverse osmosis (RO) is the same across all systems, but not all of them are built the same.

The Waterdrop G3 has eight stages of filtration, which might seem like overkill compared to the standard three-to-five-stage filters, but the difference in the purity is inarguable. My own testing showed great results. The filtered water is 100% safe for drinking and cooking.  

The eight stages comprise a cotton layer, activated-carbon filter, scale inhibitor, and reverse osmosis membrane, all of which completely eliminate harmful particles by the time the water enters your glass.

It removes chlorine taste and odor, chloramine, heavy metals, PFAS, cysts, fluoride, bacteria, and viruses, and reduces the overall TDS score. The Waterdrop G3 is also efficient against hard water, though since it’s only at the point of use, if you have a serious hard water problem, you should consider a whole-house water softener.

You don’t have to take my word for it because third-party labs have independently certified this tankless reverse osmosis system against NSF/ANSI 58 & 372 standards of water filtration. To be clear, this is not actual NSF certification, but it’s the next best thing, tested along the same standards. 

In a massive improvement for filtration eco-friendliness, the Waterdrop G3 also has a great 2:1 pure water-to-drain ratio, meaning for every two glasses of filtered water, only one glass gets wasted. Typical RO systems have a 1:4 ratio, which is not eco-friendly. 

Even though the system comprises eight-stage filtration, the water flow is still pretty decent, around 0.42 gal/min (tap water flow rate is one to two GPM) for normal water pressures. However, if your pressure falls below 30 psi, you may experience a significant reduction in flow rate. 

Another bonus is that this system has a huge capacity. It can filter a whopping 600 gallons per day (GPD). Most brands boast extraordinary capacity, but considering that the daily water consumption of an average person is only 0.5 to 1 GPD, I don’t think it’s relevant. But if you’re like me, and your in-laws like to fill their giant water bottles every time they come to your house, don’t worry. This RO system can take it because you don’t have to wait for a tank to refill. 

The design is minimalistic and compact. It comes with a smart faucet that shows TDS levels and filter life, which gives the whole system a pretty unique and tech-savvy look. 

It’s pretty easy to install and takes about half an hour without tedious labor. Also, it only takes a few seconds to replace the old filter.

Waterdrop tankless RO filter costs $599, and replacements cost $89.97, which lasts 6–12 months. The brand is also offering $80 off right now and free shipping on all its products. You’ll also get a one-year warranty and expert customer service. 


Some consumers may prefer that an expensive filter such as this have actual NSF certification instead of testing from a third-party lab. The extraordinary cleaning prowess of the Waterdrop G3 isn’t cheap. However, the replacement filter has an extremely low cost compared to NU Aqua, IcePure, Brio and iSpring.


The Waterdrop tankless reverse osmosis water filtration system is worth every penny. The eight stages are exceptional at removing the most harmful elements from your drinking water. It has a large capacity best suited for large families, even in hot summers.If you want healthy and safe drinking water all year round with no maintenance, then go for this product. Buy it today here.

2. NU Aqua Efficiency Series: 8.9/10

  • Exceptional filter life and stylish design 
  • $471.96

The NU Aqua Efficiency Series, made in the USA, has a one-of-a-kind elegant design and equally good filtering ability. Moreover, it has phenomenal filter life. 


NU Aqua has a four-stage filtration system that efficiently balances the filter quality and flow speed. Polypropylene filters, carbon-block filters, activated-carbon filters, and an RO membrane target multiple harmful contaminants present in drinking water. 

The Efficiency targets sediment, rust, chlorine, chromium, lead, fluoride, nitrates, and heavy metals. You can expect 99% removal of these contaminants. 

Even though the filter stages are fewer than the Waterdrop G3, I didn’t detect lacking performance during my testing. The water tasted good for drinking and cooking.

If you prefer your water automatically cold, you can also connect it to the refrigerator or ice maker.  Other than NU Aqua, only Frizzlife and SimPure filters have this option.  

Like Waterdrop’s system, it’s pretty efficient—it’s called “Efficiency,” after all—and has a 2:1 pure-to-waste water ratio, saving tons of water. Since it works with only four stages, you can expect high water flow rates of up to 0.5 gal/min. A built-in pump maintains a high flow rate even when the inlet pressure is low. Moreover, It has a 600 GPD capacity. 

You’ll love the smart indicator that shows TDS levels and filter life. It also comes with a leakage protection feature. 

My favorite thing about this system is its compact, stylish, tankless design with rounded edges. The system is pretty silent and fits in the smallest of places. Props to the designer. 

NU Aqua is priced at $471.96, and the replacements cost $211.85. It has three main filters, lasting 6, 12, and 36 months respectively. 


First, I ran into some issues with the adapter and fittings during installation. Nothing a quick trip to Home Depot can’t fix. You may need to adjust the fittings according to your valve, though the replacement process was fairly easy. 

Second, I noticed that the brand doesn’t have any certifications. At this price range, customers expect at least third-party quality testing. NU Aqua has countered this by offering a 120-day risk-free home trial. I guess you can have the water tested and judge the quality yourself. 

The whole system comes with a four-month warranty. At this price, I expected at least one year of warranty. 

Also, NU Aqua seriously needs to upgrade its website. It’s hard to navigate. 


NU Aqua is a good product with quality filtration and low maintenance. It removes many harmful contaminants, sediments, chlorine, fluoride, and organic compounds, but it lacks the eight-stage filtration power of Waterdrop G3. 

Nonetheless, the sleek design and fast flow rate make it a worthy second option.

Learn more about this product here

3. Waterdrop G2: 7.6/10

  • Good filtration but not for heavy-duty cleaning
  • $288.98

This reverse osmosis system, also from Waterdrop, gives an exceptional performance at half the price of the G3.


The Waterdrop G2 tankless RO system hosts five-stage filtration and is powerful enough to treat water with low to medium contamination. 

The G2 utilizes composite filter technology, which is a combo of carbon filters, a sediment filter, and a reverse osmosis membrane to clear out heavy metals, chlorine, nitrites, and bacteria. It reduces TDS levels by up to 90%, enhancing the taste significantly.

The build quality of the Waterdrop G2 tankless system is good. It’s not certified yet, but its NSF certification is under process, according to the brand. 

It comes with a stylish faucet made from food-grade material. There is also a smart display that lets you handle many features. G2’s body is leakproof and small enough to fit in tight spaces. 

You can expect a flow rate of 0.28 gal/ min and 400 GPD capacity, suitable for medium to large families. Furthermore, it has a 1:1 pure water-to-drain ratio that, while not as good as the Waterdrop G3 or NU Aqua’s Efficiency Series, is still better than a tank system. 

The Waterdrop G2 is light on the pocket and costs $288.98. The replacements are $105.98 and last for one to two years. Compared to the G3, it’s half the price, and you still get pretty good filtration. 


Contrary to Waterdrop G3, the G2 RO system isn’t powerful enough to treat heavily contaminated water. The five-stage filter does its best to filter out the most harmful elements, but you may need a pre-filter for better performance.


With advanced composite technology to clean and purify your drinking water, the Waterdrop G2 is a great option if you’re on a budget. Its tankless compact design is the most convenient to install. It’s long-lasting and extremely low maintenance. 

Learn more about this product on the Waterdrop website

4. Frizzlife PD600 

The Frizzlife PD600 is an effective tankless RO system with seven-stage deep filtration. Its effectiveness is on par with my top recommendation. 

Apart from the usual suspects, like sediment, chlorine, fluoride, nitrates, heavy metals, and bacteria, it also targets carcinogens, trichloromethane, PFOA, and PFOS and reduces overall TDS levels.

One feature that makes it stand out from the others is that the Frizzlife also has a remineralization stage that mixes essential minerals in the purified water, making it healthier and tastier by maintaining pH levels to 7.5. This feature is unique to this product and comes without any extra cost. In most cases, you have to purchase a separate filter for this. 

The Frizzlife has a drain ratio of 1.5:1 which is lower than the Waterdrop G3 and NU Aqua systems but still pretty efficient. It comes with an elegant design and a convenient LED display. 

It costs $469.99, and you’ll have to spend $33.99 every year on replacement. 

Though my test showed good results, the fact that Frizzlife PD600 doesn’t have any certification makes me a little skeptical about the quality. I’m also not crazy about the fact that the brand doesn’t have a clear warranty policy. In the same price range, Waterdrop has better products and deals. 


Next up is the Icepure reverse osmosis system, an effective and efficient system, pretty similar in design to the Waterdrop G2. Icepure has a drain ratio of 1.5:1 and a flow rate of 0.42 gal per min, which is impressive. 

Its three-stage reverse osmosis filtration system clears out most contaminants from drinking water. It isn’t as effective as five- or eight-stage filters, but it efficiently removes large particles, sediment, lead, cadmium, sodium, benzene, PFAS, and bacteria. 

The brand claims to use Sri Lankan coconut shells in carbon filters that completely remove chlorine taste and odor, but Icepure doesn’t have any certification to back its claims. However, it does provide a one-year limited warranty. 

It also effectively reduces the TDS score, but the value fluctuates, and once you open the tap, it takes at least 20 seconds for it to settle. This wastes a lot of water. 

It’s priced reasonably at $299, but the replacement filters cost $105.98. Still, it requires low maintenance and the filters last one to two years. 

6. Brio Amphora

The Brio tankless RO system has a unique design that combines style with practicality.

This system hosts a five-stage filtration setup in two cartridges, mainly comprising sediment filters, reverse osmosis membranes, and carbon filters. It filters most common contaminants in tap water but not to the extent of RO systems like Waterdrop and NU Aqua. Also, the installation is a bit difficult compared to others on the list. 

Brio water filters are NSF certified, and the build quality is adequate. However, it has a poor drain ratio and a slower flow rate of 0.20 gal per min. It can filter 100 gallons per day. 

The design is compact and fits easily under the sink. The setup also comes with a standard faucet and a pitcher that you can use to store water. The chic pitcher complements the kitchen counter perfectly, even if it’s an extra feature not everyone needs or wants. 

The Brio Amphora costs $249.99, and the replacements are $155.99. You may need to change the filters every two years. I ranked this product lower due to its inefficient drain ratio, poor flow rate, and excessively priced replacement filters. 

7. SimPure T1-400 RO+UV Filters 

SimPure tankless RO system comes with a UV filter that gives extra protection against harmful bacteria and viruses. It has a five-stage reverse osmosis system arranged in the conventional style consumers are accustomed to. 

The Simpure is effective against hard water at the point of use and reduces TDS up to 95%. The flow rate is average, around 0.28 GPM only, though it has a large capacity to filter 400 GPD. Its water efficiency is decent, with a 1.5:1 drain ratio.

The Simpure costs $299.99, and replacement is $95.96. It has four filter cartridges that last somewhere between 6 and 12 months. The brand also gives a one year warranty on this product, which is better than some of the others on this list. 

However, Simpure is not NSF certified, so if you see any claims by the brand or notice a symbol on its packaging, don’t believe it. 

8. iSpring RCS5T RO System

The iSpring RCS5T tankless reverse osmosis system is the most expensive system on my list, costing $649.99. It has a five-stage filtration system and clears out most of your everyday contaminants. 

This iSpring RO system can purify 500 gallons per day, but the flow speed is slow, close to 0.3 gal/min. At this price, I expected more. The top four products on my list give better performance at a significantly lower price. 

Be advised, the iSpring is not made in the USA, even though some of the product descriptions on online stores say so.


APEC’s RO system is compact enough for space under the sink as well as over the countertop. The sleek rectangular casing hosts four stages of reverse osmosis setup. However, the same casing makes replacing the filters a bit of a hassle. 

It removes 90% of all contaminants, but it lacks capacity compared to the top filters on my list. With only 90 gallons per day, it’s one of the lowest, so watch out for those in-laws. The flow speed is also quite slow, and it takes ages to fill a glass.

APEC’s tankless reverse osmosis system costs $279.95, and replacement filters are priced at $124.95, lasting 8 to 12 months depending upon the usage. The price is certainly lower, but I think it’s not worth sacrificing quality and efficiency. 

The Bottom Line

After reading my reviews of the leading tankless reverse osmosis systems, I hope you have a pretty good idea of what to look for in a tankless RO system. Although ranking and sorting all the products involved rigorous testing and research, it was worth it. 

The Waterdrop G3 tankless RO system performed the best out of all the filters I have reviewed thus far. The eight-stage filtration has exceptional filtering ability that can target 1000+ contaminants. It doesn’t matter if the source water is treated or not. It works just as well with well water as with city water. It’s even effective against salty and hard water. 

Usually, the higher the filter stage, the lower the water flow will be, but the Waterdrop G3 is different. It maintains a consistent 0.42 gal/min water flow speed and 600 gallons per day capacity. 

You’ll appreciate its sleek design and high-quality materials even hidden under the sink. Some may find its cost a bit too much, but high-quality filtration, easy installation, and low maintenance make it worth your money. If you want a well-rounded tankless RO system that provides superb filtration in large capacity, then order the Waterdrop G3 here.

Research Methodology

Here I explain in detail the research process and methodology I adopted to sort numerous tankless reverse osmosis systems and rank the best ones. 

Step 1: A list of tankless reverse osmosis water filtration systems

With so many brands claiming to purify your drinking water, it becomes difficult to trust any of their extravagant slogans. So, I gathered a list of the nine most popular selling products in both online and brick-and-mortar stores and ranked them according to performance, design, and certifications. 

Step 2: Product analysis 

To make the process smoother, I devised some key points based on usage, customer concerns, and expectations I had from these tankless RO systems. I came up with the following key factors: 

  • Filtering ability 
  • Targeted contaminants
  • Certification
  • Drain ratio 
  • Flow rate 
  • Compact design

This helped me sort the filter systems initially. Points for each criterion vary from highest to lowest in terms of relevancy. 

Step 3: Online reviews 

To make the process legit, I needed some insights from users as well. For that, I went through hundreds of online verified reviews people gave on authentic sites like Trustpilot, BazaarVoice, and 

I noted common issues customers faced and how each brand’s customer service handled complaints. 

Step 4: Interviews with real customers

I happen to live in Arizona, which has a reputation for bad quality water riddled with chromium and poly-fluoroalkyl substances (PFAS). Many people use reverse osmosis systems to get clean drinking water. So, I used social media to find customers near my place and planned a small interview with each one. 

To my surprise, many customer reviews were quite the opposite of what I learned in the previous step. This helped me rank the filters better. 

Step 5: Interviews with brands 

To keep things fair, I contacted the brands and asked them about the frequent complaints people brought up in the last two steps.

Some brands responded poorly, while others were quite open about their policies. I made sure to note which companies responded thoughtfully and proactively to complaints and which dismissed them out of hand.

Step 6: Test drives

Finally, it was time to see what these filters were really made of. So, I managed to build a testing rig with multiple taps. Each had roughly the same inlet pressure and flow rate. 

I connected all the filters and ran them to their maximum capacity. I then collected water samples and sent them to the certified labs for testing.

The whole process took one week. 

Step 7: Ratings

Now all I had to do was put the data into my spreadsheet and rank the tankless filters based on the points they scored in each category. Here is the list of features and specs I considered: 

  • Targeted contaminants 
  • Certification 
  • Drain ratio 
  • Flow rate
  • Filter life
  • Warranty 
  • Cost 
  • Design 

Best Tankless RO Water Filter For Pure Water

Researching and sorting through different water filters isn’t a walk in the park, but with a little effort and smart work, I ranked the top tankless reverse osmosis systems to help you pick the best one for your home and family. 

Out of them all, the Waterdrop G3 tankless reverse osmosis filter system scored the highest when it comes to performance. 

Here are some of the features that make it the best tankless reverse osmosis system: 

  • Reducing TDS score up to 99%
  • Targeting 1000+ contaminants 
  • Third-party certification 
  • High filter life
  • High water flow rate
  • Low drain ratio
  • Compact design 
  • Extended warranty 

Though the price may seem a little daunting, this filter is worth the investment. It will deliver pure and healthy drinking water all year round without any maintenance. 

For a tankless RO system that won’t waste water but will give you the cleanest water you can buy the Waterdrop G3 today and stop drinking dirty water.