Best Tankless Reverse Osmosis System of 2024

Reviewed by: James Layton
Updated on:
March 18, 2024

To determine the best tankless reverse osmosis (RO) system on the market, I followed our seven-point research methodology and narrowed down a list of over 25 systems to just five that are worth your hard-earned money. I also teamed up with James Layton, our in-house water specialist, who offered expert insight throughout the review process.

After weeks of rigorous testing, the Waterdrop G3 won the top spot due to its exceptional filtration capabilities, ease of use, and advanced features. But, of course, we’ll also look into the leading models for the best tankless RO system for remineralization, the best budget-friendly option, and the best low-key unit for small families

Best Overall Tankless RO System: Waterdrop G3P800 (9.4/10)

  • 9 filtration stages remove 99% of harmful contaminants in tap water.
  • UV sterilizing light kills 99% of bacteria and viruses.
  • Filters up to 800 gallons per day.
  • Wastes less water than other systems at a 3:1 ratio.
  • Smart faucet screen shows filter status and water quality.
  • Installation is simple and straightforward.
  • Higher up-front cost than competing brands
  • Use with well water requires pretreatment
  • Remineralization filter adds cost
  • Audible pump noise
  • Electricity required

The Waterdrop G3P800 is the best tankless reverse osmosis filter system because it uses a comprehensive nine-stage filtration process to remove over 1,000 contaminants from tap water, including dangerous pathogens.


While the Waterdrop G3P800 offers a host of impressive features, it stands out from the competition for five reasons in particular:

Pro 1/5: Exceptional filtration

The Waterdrop G3P800 is the best tankless reverse osmosis system because it uses multi-stage filtration to effectively remove 99.99% of over 1,000 contaminants in water.

First, sediment filters at the beginning and end of the filter cycle remove dirt, dust, sand, clay, etc. from your water. Two activated carbon filters eliminate harmful chemicals such as chlorine, chloramine, VOCs, herbicides, and more. Sandwiched in between these carbon filters is a 7-layer RO membrane to trap almost everything else, including lead and fluoride. Lastly, the water passes through a UV sterilizer to zap bacteria and viruses.

All of this means that if your tap water is contaminanted by any sort of chemical, heavy metal, or unwanted living organism, you should get the Waterdrop G3P800.

Pro 2/5: High-capacity filtration 

The second impressive feature of the G3P800 is its capacity to filter up to 800 gallons per day (GPD). One common downside of most RO systems, especially those with tanks, is their low filtration capacity. This is because the water has to go through numerous filtration stages before it’s sent to the tap for consumption. Also, if you’ve emptied the tank to fill multiple water bottles or fulfill other water-heavy tasks, it takes time for it to fill up, reducing your water access and costing you extra time you may not have. 

However, with the G2P800’s high-capacity design, you get a potential daily output of 800 gallons of purified water. This high capacity means you basically can’t run out of purified water. In practical terms, the potential 800 GPD capacity means the system can handle increased water use by more than a few people or challenges posed by a few contaminants or many. 

While the average household may not require 800 gallons daily, this ample capacity ensures consistent and high-quality purified water, even during peak usage periods. This feature makes the Waterdrop G3 suitable for a variety of households, even those with heavily contaminated water, ensuring users always have access to clean and safe drinking water.

Pro 3/5: Low water wastage 

The third pro is how much the Waterdrop G3 impressed our team with its efficient water-saving technology, which minimizes water wastage compared to other tankless reverse osmosis systems. For every three gallons of purified water this system produces, it only wastes one gallon of dirty water. 

This is achieved with an advanced water recovery system that optimizes the filtration process. The G3 features a high-efficiency RO membrane that retains contaminants while allowing more water to pass through, reducing the amount of water sent to the drain. The system also incorporates a smart internal recirculation pump that recycles wastewater to further enhance water efficiency. This innovative design ensures the lower pure-to-drain water ratio of 3:1, making the G3 one of the most water-conscious choices among tankless RO systems. This performance is particularly noteworthy considering most reverse osmosis systems have a 1:1 or 2:1 ratio.

This pro is massive because it saves you money in the long run. You can rest assured that your water bill won’t skyrocket as a result of your new water treatment system. Since the system produces three gallons of purified water for every gallon of wastewater generated, you also don’t have to worry that your clean water comes with a cost to the environment. If you want to save money and the environment, the Waterdrop G3P800 is the reverse osmosis system for you.

Pro 4/5: Effortless maintenance and straightforward installation

The fourth major benefit of the Waterdrop G3P800 is its small size, which makes for easy installation and trouble-free maintenance. Like most tankless reverse osmosis systems, the G3P800 system occupies roughly 70% less space than traditional RO models, making it super easy to install. You see, under-sink reverse osmosis systems with tanks often take up so much space that they’re difficult to maneuver for installation. The large tanks also mean there’s no room for cleaning products, a wastebasket, or whatever else you might want to store under your sink. Unlike those bulky systems, the G3P800 is tall and skinny. You can set it up in one corner and have plenty of storage space under your sink. You’ll also enjoy the easy filter replacement process. With a quick-twist mechanism, users can efficiently remove old filters and replace them with new ones within seconds. You can even bundle-order the replacement filters and save at least $10.

The system arrives with a thorough installation kit, including a drain saddle (used to make a wastewater connection with the drain under the sink) and fittings, ensuring users have all the necessary components for a straightforward setup. Waterdrop also provides a YouTube video that guides you through the installation process. You should bear in mind that this system requires a hole for a dedicated smart faucet. If your sink does not have an existing hole, you will need to drill one. Waterdrop will also sell you a separate accessory kit that includes a one-liter pressure tank and connections that let you connect your RO system to your refrigerator’s ice maker and dispenser

If you need a system that’s easy to set up and operate, the Waterdrop G3P800’s small size and DIY-friendly installation offer a sleek and minimalist solution that makes it an ideal option for those who prefer not to have a bulky RO drinking water system and tank taking up valuable space under the sink.

Pro 5/5: Smart faucet with digital display

The final cracking feature that sets the G3P800 apart from the competition is its smart faucet, which features an LED screen that provides real-time information about your water quality. The smart faucet is equipped with a total dissolved solids (TDS) monitor and digital display. This feature allows users to gauge the quality of their filtered water by providing real-time information about TDS levels.

The smart faucet’s LED indicators also include the status of the filters. By lighting up or changing colors, the LED function reminds users to replace filters when necessary, ensuring the continued effectiveness of the water purification process. However, the only available faucet color option is brushed aluminum. While this may be a minor concern for some users, those with specific kitchen design preferences may find the lack of customization limiting. What they won’t find limiting is the modern digital display.

Anyone who’s ever used a filtration system knows that while they’re generally pretty great, they can be hard to keep track of. Is it working? Does the filter need replacing? With the P800’s smart features, you don’t have to wonder. If you want to see the status of your water quality and filter media right there at the faucet, you’ll get a kick out of the Waterdrop G3P800.


Like any product, the Waterdrop G3P800 has three drawbacks you should consider before investing:

Con 1/3: Higher up-front cost than less-comprehensive tankless RO systems

As you compare systems, you’ll find that the Waterdrop G3P800 has a higher price tag than some other tankless RO systems on the market. With the UV filter included and its other impressive features, this comes as no surprise.

Adding to the cost is the fact that the remineralization feature is extra. Why would you need one of those? Well, one common criticism you’ll hear about reverse osmosis is that it removes essential minerals. Even though most people get enough of these minerals from food, some users want to add those minerals back in. And you can! But it’s extra. Remineralization is not necessary for the system’s primary function of removing contaminants from the water, but it is an important feature for those who believe they need to get minerals from their water.

Despite the high cost, users typically report that the system’s performance and innovative design justify the investment over time, especially when factoring in its impressive filtration capacity and reduced utility costs. The filters also last longer compared to traditional RO systems. Filter replacements are affordable, and you can choose the two-year combo replacement filter bundle at a discounted price for added peace of mind. But the one-year warranty for potential manufacturing defects or malfunctions may not impress most people. 

Luckily, you do get a 30-day money-back guarantee that allows you to return the system within this time frame for a refund if you aren’t satisfied with your purchase. While no restocking fee is charged (a rare concession), you’ll still be responsible for return shipping if you choose to return the product. At the end of the day, the Waterdrop G3P800 is well built and performs well, so the short warranty is unlikely to be an issue. But if you’re looking for a low price and an enviable warranty, you might want to look into the Nu Aqua Efficiency Series, which I’ve reviewed below.

Con 2/3: Not ideal for well water without pre-filtration

Another drawback to the G3 is that Waterdrop is adamant that the G3P800 should NOT be used to filter well water that hasn’t been pretreated with a sediment filter. In fact, using it with well water could void your warranty. Well water often contains larger particles, mostly sediment, which can potentially clog the delicate RO membranes, affecting the system’s efficiency. Installing a sediment filter before your RO system can help remove the larger particles, and luckily, sediment filters are among the cheapest filters out there.

See our review of the best sediment filters to set your home up for the G3P800 right away. 

To use this system with your well water, we recommend investing in a sediment pre-filter or one of the best whole-house well water filters as a pre-filtration option to prevent the costly damage caused by iron, manganese, sulfur, and other contaminants to your health, appliances, and plumbing fixtures.

Con 3/3: Audible pump noise

Another aspect you need to be aware of is the audible pump noise, which operates at 65 decibels (dB) during regeneration. While the noise level is comparable to background conversations, it may be noticeable in quiet environments, potentially causing disturbance for light sleepers if the system is installed close to bedrooms.

On top of being rather loud, the pump requires electricity. This is not unique to the Waterdrop G3. Electricity dependency is a common downside to most tankless RO systems. In fact, you should keep this in mind as you consider the other tankless filters on this list. While this facilitates impressive flow rates and filtration capacity, it may pose a challenge in situations where electricity interruptions occur, potentially disrupting the continuous supply of purified water. Users in areas prone to power outages should consider this dependency when evaluating the system’s suitability for their homes.

It might be a good idea to have a water filter pitcher on hand for such emergencies. Luckily, we’ve compiled a list of the best water filter pitchers for well water

OVERALL: 9.3/10

The Waterdrop G3P800 tankless reverse osmosis system is the best overall tankless RO system on the market because it offers a high filtration capacity, efficient water usage, an integrated UV sterilizing light, and a smart-faucet digital-display screen.

Some may balk at the higher up-front cost at first but soon realize that the included UV filter for killing pathogens justifies the cost, as do the low maintenance expenses and low wastewater ratio, which translates to reduced water bills.

If you’re looking for a high-performance, space-saving, and efficient water filtration system, this is the perfect choice for you. Order your Waterdrop G3P800 tankless reverse osmosis system today and experience the difference it makes in your home’s water quality.

Best for Remineralization: SimPure T1-400ALK (8.7/10)

  • 7 stages remove 1,000+ contaminants from tap water.
  • UV filter kills 99% of bacteria and viruses.
  • Alkaline stage increases pH of acidic water and adds minerals.
  • Water pressure gauge monitors maintenance needs.
  • Can connect to a refrigerator and ice maker.
  • Great price considering UV and remineralization are included.
  • Lower filtration capacity than other models on this list
  • Requires electricity
  • Not suitable for well water without pre-treatment

The SimPure T1-400 ALK is the best tankless RO system for remineralization because it comes at an excellent price and is highly effective against many contaminants, including bacteria and viruses, all while adding essential minerals and improving the taste of your drinking water.


Three significant pros make the SimPure tankless RO system stand out as the best for remineralization among all the filters on this list:

Pro 1/5: Seven-stage effective filtration process

The SimPure under-sink RO water system is the best remineralization filter because it effectively removes 99.99% of over 1,000 contaminants, including viruses, bacteria, chemicals, heavy metals, PFOA/PFOS, pharmaceuticals, and more, ensuring the delivery of clean and safe drinking water. It is also capable of reducing the TDS levels to below 25 PPM or lower.

It achieves this through its seven-stage filtration process. A sediment filter removes large particles, such as sand, dirt, and rust. A granular activated-carbon filter removes chlorine, odor, and bad taste and a carbon block filter removes residual chlorine, organic matter, and other harmful substances. The RO membrane filter then removes over 1,000 harmful substances, such as TDS, fluoride, arsenic, chromium, radium, and more. The next stage features the post-carbon filter, which further removes any remaining sediment and impurities. In the penultimate stage, the alkaline filter adds beneficial minerals back into the water. Lastly, the UV purifier destroys up to 99.99% of viruses and waterborne parasites.

You can trust the SimPure to produce clean, safe water for you and your family. Whether you’re 

Pro 2/5: 400 GPD filtration capacity and low drain ratio

The second pro of the SimPure T1-400 ALK is its 400 gallons-per-day (GPD) filtration capacity and consistent flow rate of 0.28 gallons per minute. It can fill a cup in 12 seconds thanks to its booster pump. While it may not rival the Waterdrop G3’s impressive 800 gallons per day capacity, it’s enough to serve the needs of a family of four or six. In any case, you don’t really need 800 gallons a day unless you’re hosting an army.

Additionally, the system maintains an eco-friendly profile with a low 1.5:1 drain ratio, efficiently utilizing water resources by producing only 1 gallon of wastewater for every 1.5 gallons of pure water.

Pro 3/5: Water pressure gauge

Third on our list of outstanding features is the SimPure T1-400 ALK’s water pressure gauge, a smart and practical feature that helps users monitor their system’s performance. The built-in pressure gauge allows users to monitor the feed water pressure, which should ideally be between 15–60 PSI for the system to function effectively. When the water pressure lowers, it’s a sign the filters need replacement. The SimPure T1-400 ALK may not have filter life indicators, but the water pressure gauge performs the same function.

Pro 4/5: Connects to your refrigerator and icemaker

The next unique benefit to the SimPure tankless RO system is that you can connect it to your refrigerator and icemaker if you want. It comes with all the supplies you need. Once the system is connected, it can provide you with clean, great-tasting, AND cold water or ice, free from impurities and contaminants. 

However, it’s important to note that when the T1-400 ALK RO system is connected to the refrigerator/ice maker at the same time, the water flow rate may slow down, and additional tubing or a delivery pump may be required depending on the installation distance. 

While under-sink reverse osmosis is widely popular, many users lament that cold water and ice from the refrigerator are not as trustworthy as their RO water. Not with the SimPure T1-400 ALK. You can have ice-cold water free from contaminants with the SimPure’s refrigerator connection capability. 

Pro 5/5: Included remineralization filter 

Lastly, and what you’ll probably love the most about the SimPure T1-400 ALK, apart from the UV sterilizer and everything else I mentioned above, is the alkaline remineralization filter. The RO process removes minerals from the water, including calcium and magnesium, which are alkaline minerals. Some people think these minerals help water taste better, while others don’t notice the taste of water at all. Remineralization not only adds essential minerals, it can also balance the pH of reverse osmosis water. 

This filter uses calcium carbonate, magnesium carbonate, and potassium carbonate to add minerals back to the water. These carbonates are also what raises the pH of acidic water, which a lot of reverse osmosis water is, to a pH of +7.0. Calcium carbonate does not dissolve in water unless it is acidic. The more acidic the water, the more the calcium carbonate dissolves. The carbonates neutralize the acidic water and raise the pH.

According to some recent research, the alkaline remineralization filter might also reduce the oxidation reduction potential (ORP) of the water, which might help reduce the amount of free radicals in the body. If you’re looking for a water filter that can provide good-tasting water AND potentially improve your health beyond simple hydration and lack of contaminants, remineralization is definitely for you.


While the SimPure T1-400 is a good and efficient system, there are three issues you need to consider before purchase:

Con 1/3: 400 GPD filtration capacity isn’t for heavy water needs

The SimPure T1-400 ALK’s 400 GPD filtration rate falls slightly behind competitors like the Waterdrop G3P800 and Nu Aqua Efficiency Series, which boast higher capacities. This difference might impact households with exceptionally high water demands. Additionally, the 1.5:1 drain ratio is decent, but a lower drain ratio means more efficient water use and reduced waste. However, the SimPure T1-400 ALK still provides substantial filtration capacity and efficiency for many households, particularly those with average water consumption needs.

Con 2/3: Requires electricity

Similar to the Waterdrop Tankless RO filter, the SimPure T1-400 ALK requires electricity to work. Depending on the layout of your kitchen, this might mean running a wire to an outlet, or perhaps sharing power with the undersink garbage disposal. While this is a common feature in tankless RO systems, it could also be an inconvenience and is something to consider before purchasing.

Con 3/3: Not suitable for well water without pre-treatment.

The third downside of the SimPure T1-400 ALK is that it is not suitable for well water unless you properly pre-treat it. This is because the most common well water contaminants, such as iron, sulfur, manganese, as well as hardness minerals such as calcium and magnesium, can foul an RO membrane and dramatically reduce its lifespan.

The solution to this is to add a pre-filter that can handle these contaminants and lighten the load on your RO system, which will make it more effective and allow it to last longer. Of course, this could significantly raise the cost of your entire system and is something to keep in mind.

OVERALL: 8.5/10

The SimPure T1-400 ALK is one the best remineralizing tankless reverse osmosis systems on the market due to its alkaline stage, UV filter, and refrigerator connectivity capability. Its seven-stage water filtration effectively removes 99% of contaminants, including heavy metals, chemicals, chlorine, PFAS/PFOA, microbial bacteria, providing a reliable source of clean, pure, and great-tasting water for households.

While it boasts an impressive array of features, including a UV sterilizer, its lower 400 GPD filtration capacity might be considered a drawback for users with higher water demands compared to the Waterdrop G3 P800. However, the SimPure T1-400’s comprehensive filtration process, alkaline stage, and UV sterilization make it a worthy choice.

For healthy minerals and balanced pH, get the SimPure T1-400 ALK today.

Best Budget Option: Nu Aqua Efficiency Series (8.9/10)

  • Three-stage filtration removes 99% of contaminants from tap water.
  • Comes with a budget-friendly price tag.
  • Filters up to 800 GPD.
  • Comes with a lifetime warranty, 120-day guarantee, and 24/7 support.
  • Installation and operation are super easy.
  • Super-quiet booster pump keeps noise to a minimum.
  • UV and alkaline filters sold separately
  • Low pure-to-waste ratio
  • Not ideal for well water
  • No water quality tracking
  • Needs electricity connection

The Nu Aqua Efficiency Series is the second-best tankless RO system because it removes 99% of contaminants from water while maintaining a high filtration rate at a price more homeowners can afford.


The Nu Aqua tankless reverse osmosis system is a powerful and efficient water treatment system that produces great-tasting water at a budget-friendly price. But the price tag isn’t the only reason to choose this system. Four particular benefits stand out:

Pro 1/4: Effective filtration

First, and most importantly, the Nu Aqua Efficiency Series tankless reverse osmosis system provides effective filtration by removing up to 99% of contaminants from city water, including heavy metals, fluoride, chlorine, VOCs, bacteria, pesticides, chlorine, and many more. If you were expecting the budget option to offer inferior contaminant removal, I’m delighted to tell you it doesn’t.

This system employs a three-stage filtration process to ensure the delivery of high-quality, purified water. In the first stage, spun polypropylene and carbon block filters effectively remove sediment, rust, chlorine, and larger particles from the water, extending the lifespan of the other filters in the system. The second stage uses a granular activated carbon filter (GAC) to remove pesticides, lead, various metals, arsenic, asbestos, and mercury while also improving the taste and eliminating odors from your water. The third stage features the reverse osmosis membrane, which is a powerhouse at eliminating heavy copper, hexavalent chromium, lead, fluoride, nitrate, and salts from water. 

The system’s efficient removal of contaminants makes it a reliable and efficient option for those looking to improve their home’s water quality. 

Pro 2/4: High filtration capacity

As if that first pro wasn’t good enough, the Nu Aqua Efficiency Series tankless reverse osmosis system boasts a commendable 800 gallons per day filtration capacity — that’s up to 800 GPD, mind. If your water is heavily contaminated, expect it to be lower. If you ever reach the limit, though, that would be most impressive. 

It achieves this capacity through a combination of the silent and powerful booster pump, which allows for faster and more efficient filtration, and the internal channel filter design, which directs water through all filter media, allowing for thorough contaminant removal and efficient water usage. 

Whether it’s filling up multiple glasses for multiple guests or filling a pot to boil, the Nu Aqua provides the convenience of a substantial amount of purified water readily available.

Pro 3/4: Easy operation and installation

The third thing you’ll love about the Nu Aqua Efficiency Series is how easy it is to install and manage, with straightforward instructions and user-friendly features. The system comes with a detailed installation manual, and the unit arrives with color-coded tubing and quick-connector fittings, making the installation process intuitive and efficient. Nu Aqua also offers a 24/7 customer support line and a live-chat feature on its website, along with a team of experienced technicians who can help troubleshoot any problems. 

If you are comfortable with basic plumbing and DIY projects, you should be able to install the system yourself. (However, if you are not comfortable, consider hiring a professional plumber.) You could have it up and running in under an hour. 

The system is easy to use as well. Initial operation includes flushing the system to remove any residual particles from the filters and the RO membrane. After flushing, the system is ready to use. Flushing just means running the faucet and discarding the water. All you need to do is monitor the filters through the LED indicator on the faucet. The RO membrane can last up to 36 months, and the filter changes only take 20 seconds.

Even though just like the Waterdrop G3 the Nu Aqua system requires electricity to run, you’ll appreciate the ultra-silent booster pump integrated into the system. You won’t have to worry about a constant humming coming from under your sink.

Pro 4/4: Budget-friendly price, lifetime warranty, and more

Finally, while it’s not the cheapest option on the market, the Nu Aqua Efficiency Series is the best budget-friendly model because it also removes 99% of contaminants, has the potential to filter up to 800 gallons per day, and comes with an enviable warranty. Not every low-priced model can boast stats like that. With the Nu Aqua, “budget friendly” doesn’t have to mean “less effective.” The system’s lower initial cost simply allows users to enjoy the benefits of a high-capacity tankless RO system without the premium associated with advanced features, which not everyone wants or needs.

The Nu Aqua system also has a great warranty, money-back guarantee, and 24-hour customer support. The lifetime warranty takes effect once you subscribe to Nu Aqua’s filter replacement service. Joining saves you an extra 10% and eliminates the need to buy new filters at the last minute. Nu Aqua also offers a 120-day money-back guarantee during which users can assess and evaluate the system’s performance and suitability for their needs. 

Homeowners have a lot of gadgets and appliances to buy these days, and a water treatment system that won’t break the bank helps you save money for emergencies. The impressive lifetime warranty protects your investment, and the filter replacement subscription keeps your filters coming regularly at a price you can afford. If you want to save money on a comprehensive system, get the Nu Aqua Efficiency Series.


Before you buy the Nu Aqua Efficiency Series, you need to consider the four factors below and see if they fit with your needs.

Con 1/4: UV and alkaline filters sold separately

If you’re hoping for an all-inclusive system, you may not want to go for the budget-friendly option. Additional types of water treatment are extra with the Nu Aqua. For example, if you want to raise the pH of your water or add essential minerals back into your water, you’ll have to pay extra. And if you have bacteria or other pathogens in your water, you’ll also have to pay extra for a UV filter.

Even though alkaline filters are a bit of a trend, not necessarily a necessity, many users believe adding minerals back into the water and adjusting the pH balance improves its taste. Without this filter, the water produced by the system may not have the same fresh taste as water that has been mineralized. Similarly, the UV sterilization feature is an important component that ensures the efficient removal of bacteria and viruses from the water. 

The fact that these filters are sold separately may deter some users from purchasing the system, but if you’re on city water, you don’t need to worry about pathogens because the water is disinfected by the government. And if you’re confident you get enough minerals from your diet, this con won’t apply to you. 

Con 2/4: Low pure-water-to-waste-water ratio

Another downside to consider is the lower pure-water-to-waste-water ratio. The Nu Aqua Efficiency Series, at 2:1, may not impress the more environmentally conscious among us. In the Nu Aqua, every two gallons of clean water wastes one gallon of untreated water. 

The higher wastewater output can impact water bills and overall environmental sustainability, so you’ll want to take that into account when shopping for a reverse osmosis system. However, it’s worth mentioning that some reverse osmosis systems waste more water than they clean, so this ratio could be much worse.

Con 3/4: Not ideal for well water without pre-filtration

Like the Waterdrop G3 (and most reverse osmosis systems), the Nu Aqua requires a pre-filter if you want to use it with well water. The system is equipped with a powerful 800 GPD reverse osmosis membrane that eliminates heavy metals and other contaminants from water, but well water may contain a high level of total dissolved solids (TDS) and other impurities that could affect the system’s performance and longevity. 

So, well water may require specific pre-filtration or conditioning to get the most out of the Nu Aqua Efficiency. Therefore, you really should conduct a thorough water test and, if necessary, consult with the Nu Aqua technical support team to determine the suitability of the NU Aqua tankless system for filtering a specific well water source.

Con 4/4: No water quality tracking

Sadly, the Nu Aqua has few smart features to speak of. While not essential to the primary function of treating water, modern features such as ongoing water quality information provide users with enhanced monitoring and control over their water purification system.

In contrast, the lack of such advanced functions in the Nu Aqua Efficiency Series limits users’ ability to conveniently track the system’s performance in real time, resulting in a less streamlined and interactive user experience compared to the Waterdrop system’s technologically advanced features. The Nu Aqua has a filter life indicator, but if you’re looking for the latest in modern technology, you won’t find it with the Nu Aqua. 

However, if you’re attracted to the Nu Aqua because it’s budget friendly, no doubt you don’t want to be distracted with all the newest bells and whistles anyway. If you’re not looking for real-time water quality data, the Nu Aqua Efficiency Series tankless reverse osmosis system is for you.

OVERALL: 8.8/10

The Nu Aqua Efficiency Series 800 GPD tankless reverse osmosis system is the best budget-friendly tankless RO system due to its low price, potential 800 GPD filtration capacity, and trustworthy comprehensive filtration of many common residential water contaminants. 

While it may not include UV purification or remineralization, it offers an effective four-stage filtration process and the same space-saving design as other tankless reverse osmosis systems. Add to that the lifetime warranty with a 120-day return guarantee and you’ve got a practical and reliable choice for improving your home’s water quality.

If you’re in the market for a budget-friendly and effective tankless RO system, the Nu Aqua Efficiency Series is the best you’ll find.

Best for Small Families: Waterdrop G2 (8.2/10)

  • Removes 99% of contaminants and reduces TDS by 94%.
  • Priced for budget-conscious households.
  • Adding remineralization is easy and affordable.
  • Filtration capacity of 400 GPD is perfect for small households.
  • Smart LED lights remind you to change the filters.
  • Saves 70% of under-counter space.
  • 12-month filter life reduces replacement costs and maintenance.
  • Lower drain ratio
  • Limited features
  • Needs electricity to work
  • Short warranty
  • Not suitable for heavy-duty filtration
  • Well water needs pre-filtration

This system is the best tankless reverse osmosis system for smaller families, providing an affordable yet effective solution with its space-saving design, five-stage filtration, and long filter life at an affordable price point.


The Waterdrop G2 is the best reverse osmosis filter for small families for four main reasons:

Pro 1/4: Efficient filtration

First, the Waterdrop G2 tankless reverse osmosis system does exactly what it promises. It removes 99% of known water contaminants, including fluoride, chlorine, lead, VOCs, arsenic, cadmium, TDS, atrazine, salt, nitrates, PFAS, and heavy metals. Additionally, the system’s 0.0001μm (micrometer) RO membrane has been tested to reduce TDS by 94%.

The filtration process of the Waterdrop G2 consists of seven stages designed to remove these contaminants from your water, ensuring high-quality purified water in every glass. The first stage of the filtration process is a sediment polypropylene (PP) membrane that filters out larger particles, such as dirt, dust, and sand, preventing damage to the subsequent filters and membranes. The water then passes through an activated carbon block filter, which adsorbs and filters out volatile organic compounds (VOCs), chlorine, and other organic contaminants, improving the water’s taste and odor. 

The water next passes through an inhibitor layer that helps extend the service life of the RO membrane, then a second sediment PP membrane, which further filters out any remaining sediment and particles. The RO membrane is next, efficiently removing heavy metals, salts, and 1,000+ contaminants. The water then passes through a second activated carbon block filter, which further improves taste and water quality. Finally, the water goes through a polypropylene membrane that intercepts any remaining impurities. 

This thorough filtration not only enhances the quality, taste, and odor of your water but also contributes to the overall health and well-being of your family, making the Waterdrop G2 a reliable choice for anyone seeking a budget-friendly and small but efficient tankless reverse osmosis system.

Pro 2/4: Affordable, even with remineralization

Second, you’ll appreciate the price of this unit. It’s almost half the cost of our most budget-friendly choice. The only reason the Waterdrop G2 didn’t win that spot is that this one is better for lower water needs, like those of one or two people. But that doesn’t mean it doesn’t offer great features at an equally great price. 

For example, for an extra $29, you can add a remineralization filter. This filter uses natural materials to restore minerals, including calcium, magnesium, sodium, and potassium into the water. It uses precipitated calcium carbonate to simulate the formation mechanism of mineral springs and adds 18 different beneficial minerals and trace elements to the filtered water. This raises the water’s pH level to an alkaline level (pH 7.0+), providing superior taste and reported health benefits. 

While you can add the remineralization filter to the Waterdrop G3P800, as well, that system is designed for large families at a much higher price. The G2’s price point makes remineralization available to smaller families who may be just starting out and operating with a smaller budget. At this price point, it can’t hurt adding an extra $29 to improve the taste of your drinking water and save on single-use water bottles. This filter also has a 12-month lifespan, so you don’t have to replace it often. If you’re a single person or couple and you don’t want to pay large-family prices, you should get the Waterdrop G2 tankless reverse osmosis system.

Pro 3/4: Low-key maintenance and easy installation

The third thing to love about the G2 is how low-key it is. Like most tankless reverse osmosis systems, the Waterdrop G2 system is designed for easy installation. All components necessary for installation, such as the dedicated faucet, feed water adapter, and drain saddle, are included along with a detailed user manual, and the average person can install it in approximately 30 minutes. Additionally, this is one of the most compact systems on the market. In fact, it saves even more under-sink storage than the Waterdrop G3P800. 

Replacing the filters is easy too. The system features a twist-and-pull design for convenient filter replacement, allowing users to replace the filter in 3 seconds with a single twist and no tools required. Speaking of the filter, the system’s 2-in-1 composite filter has a lifespan of 12 months, or 1,100 gallons of clean water, based on water conditions. This long service life makes the G2 a practical and efficient choice for those seeking a reliable water filtration system for their homes. The system is also equipped with smart LED filter indicators. While simpler compared to the G3 model, these lights alert users to the optimal timing for fresh filters, ensuring consistent water quality and system performance.

If you’re looking for a low-key system that isn’t fussy to install and maintain, get the Waterdrop G2.

Pro 4/4: Perfect for small families

Lastly, the Waterdrop G2 model is particularly suitable for single people or couples just starting out. With a filtration capacity of 400 gallons per day (GPD), it provides a reliable and continuous supply of purified water for smaller households with lower water consumption. This capacity allows users to fill a glass of water in around 12 seconds. Unlike its bigger sibling, the G3P800, which has a higher capacity and a lower drain ratio, the G2 has a 1:1 drain ratio meaning for every gallon of filtered water it produces, it wastes another gallon. This puts it at par with traditional RO filters. 

The 1:1 drain ratio may seem low, but for one to two people, it’s not wasting much water because you’re not using as much water. If you don’t need a high filtration capacity and a high drain ratio, why pay for it? With the G2, you still get the contaminant removal you need but without all the bells and whistles a young family on the go doesn’t really need. You don’t want to pay extra for the G3’s oomph if you don’t need to, so save money and get the equally effective Waterdrop G2


The Waterdrop G2 has four limitations that may put off those looking for a fancier system.

Con 1/4: Not resource efficient

The main con of the G2 is its low 1:1 drain ratio. What this means is that one gallon of water is wasted for every one gallon of water cleaned. Even though this isn’t rare among reverse osmosis systems, it’s still a drawback in terms of water conservation, especially in regions where water scarcity is a concern. 

If water conservation is a concern of yours, get either the Waterdrop G3 or the Nu Aqua 800 GPD models, both of which showcase better water efficiency with higher drain ratios, making them more environmentally friendly and cost-effective over time. With the G2, you may notice an impact on your water bill due to the increased consumption associated with the less efficient use of water during the filtration cycles.

Also, like the other previous systems we’ve looked at, this system needs electricity to power the pump. Some reverse osmosis systems use your home’s water pressure to power the movement of water across the filtration stages, but these systems require electricity. Of course, most of the appliances in your home require electricity, so it’s not as if this is out of the question. And as I explained above, since the Waterdrop G2 is most suitable for single people or couples, the difference may not be very noticeable in the long run.

Con 2/4: Limited features

Another notable drawback is that while the G2 removes the required contaminants, it lacks some of the advanced features present in the G3, such as the integrated UV sterilizing light and smart faucet screen for real-time information. However, if you’re looking for a simple system to provide clean drinking water for one or two people, smart features may not be on your list of must-haves anyway. If you don’t care about fancy features, get the Waterdrop G2.

Con 3/4: Short warranty

The Waterdrop G2 and G3 both come with a one-year warranty, which isn’t terrible, but it’s not the best either. While the warranty provides users with a certain level of assurance, a more extended warranty period would offer more peace of mind, especially considering the long-term investment involved in a water filtration system. If you prioritize an extended trial period and wider coverage, Nu Aqua’s lifetime warranty, coupled with a better money-back guarantee of 120 days, provides users with a relatively longer time frame to assess and experience the product. If your priority is a long warranty period, look into the Nu Aqua Efficiency Series.

Con 4/4: Not suitable for heavy-duty filtration and well water

The Waterdrop G2 may not be suitable for heavy-duty filtration needs due to its smaller filtration capacity compared to more advanced systems like the Waterdrop G3P800, but that’s what makes it the best filter for single people and couples. With a filtration capacity of up to 400 gallons per day, the G2 is designed to cater to smaller households or individuals with lower water consumption. For users seeking a robust filtration system capable of handling larger volumes of water, addressing heavy-duty filtration requirements, and accommodating a higher flow rate, upgrading to a system with a larger capacity, such as the Waterdrop G3P800 or the Nu Aqua Efficiency Series, might be a more appropriate choice.

And just like the G3, the Waterdrop G2 is not suitable for well water filtration primarily due to the potential presence of large particles and variations in water pressure often associated with well water sources. Using this system for well water could void your warranty. Users with private wells are advised to consult with technical support representatives before considering these systems to ensure compatibility, and in many cases, installing a sediment pre-filter might be necessary to address specific challenges posed by well water.

OVERALL: 8.2/10

The Waterdrop G2 is the best tankless RO system for small families because it’s an affordable yet highly effective solution for users seeking reliable water filtration without spending unnecessary dollars on a high filtration capacity and fancy features they don’t need. 

While the Waterdrop G2 excels in affordability and efficient filtration, it does have a lower pure-to-waste water ratio compared to the G3, which might impact water conservation. However, its fast flow rate, five-stage filtration process, and filter-life indicators make it an excellent choice for young people or small families prioritizing budget without compromising on water quality.

If you’re a single person or couple looking for a low-key and efficient solution to improve your home’s water quality, this is the ideal choice for you. Go ahead and purchase the Waterdrop G2 today!

Honorable Mentions

One reverse osmosis system we reviewed doesn’t stand out for any one particular function, but it’s still a pretty good system worthy of mention.

Frizzlife Tankless RO System

The Frizzlife tankless system caters to individuals looking for a tankless reverse osmosis system with alkaline remineralization capabilities. It’s another excellent choice for those who prioritize not only pure water but also the restoration of essential minerals. 

It can remove more than 1,000 contaminants from water at a rate of 99.99%, including sediment, chlorine, fluoride, nitrates, heavy metals, bacteria, carcinogens, trichloromethane, PFOA, and PFOS. It achieves this through its three dedicated filters with seven filtration stages. However, the system is particularly suitable for users who appreciate the health benefits of drinking alkaline water and desire a smoother, mineral-rich taste.

The Frizzlife is a good option due to its tankless design, compact footprint, and high water flow rate of 600 gallons per day (GPD), making it suitable for large families with high water consumption needs. Its 1.5:1 low drain ratio is average; it’s not the lowest, it’s not the highest. But the inclusion of a smart LED display and filter life indicators enhances user convenience, providing real-time information about water quality and timely reminders for filter replacements. So that’s nice.

However, the Frizzlife PD600 faces stiff competition from other tankless systems on our list. For example, its warranty can’t compare to the Nu Aqua, and its drain ratio is not nearly as good as the Waterdrop G3. As a remineralization filter, it doesn’t quite match up with the SimPure T1-400’s other unique features, and it’s not as affordable and simple as the Waterdrop G2, even if it has a slightly better drain ratio. 

Despite these cons, the Frizzlife PD600 offers a solid option for users seeking alkaline remineralization in a tankless system. While it might not claim one of the top spots, its unique features and capabilities make it a viable choice for those with specific preferences in their water filtration systems.

Bottom Line: The Best Tankless RO Systems for Your Home

The Waterdrop G3 is the best overall tankless reverse osmosis system among its peers because it has the most impressive stats. Its exceptional filtration, hard-working 800 GPD capacity, and included UV purifier will provide your home with a continuous supply of clean and purified drinking water. And its modern digital-display screen is simply unrivaled.

The SimPure TI-400 is the best system if you want remineralization and UV included from the get-go. For a budget-friendly system, the Nu Aqua Efficiency Series 800 GPD tankless system is the best because it combines high filtration capacity and a robust warranty with an affordable price. The Waterdrop G2, on the other hand, caters to small families seeking alkalization and remineralization but not all the fancy extra stuff. 

As you navigate the world of tankless RO systems, consider your specific needs and preferences. We invite you to share your thoughts in the comments or reach out with any questions. Our goal is to empower you to make the best choice for your household’s water filtration needs.

Research Methodology: How We Test and Review Products

With so many options available on the market, choosing the perfect tankless reverse osmosis filter for your home is not easy. That’s why, here at Drinking Water, we employ a seven-point research methodology to properly evaluate each and every product available. We blend qualitative and quantitative data to make sure we cover all aspects of the product.

This strategy allows us to carefully filter through the many options and find those that are actually worth your money. Below is a summary of how we carry out the research process.

Use analysis

The first step in the process is to categorize the systems according to their specific use. This helps us understand how these systems respond to specific problems in household water supply. Some of the things we look at include water source compatibility (for either city or well water), types of contaminants the filters remove, and compatibility with other filtration systems and household appliances and fixtures.

Learn more about how we conduct our use analysis.

Tech check

Next, we look into the technology integrated within these tankless reverse osmosis systems to make sure they’re not just gimmicks but actually bring real benefits to the user. Most manufacturers like to use technical buzzwords in their marketing material just to upsell their products. It’s our job to make sure that these systems work like they say on paper.

Read more about how we conduct tech checks.

Water test data

Most brands usually run their products through a series of third-party tests to make sure they abide by government regulations and also to ensure the systems work as advertised. Some well-known organizations that run these tests include the Water Quality Association and the National Sanitation Foundation. For this stage in the research process, we try to obtain this data from the manufacturers to help us prove that their systems work as they claim. In the absence of this data, we carry out our own in-house tests.

Learn more about how we check water test data.

Installation test

After checking the water test data, we install these tankless systems to learn if the installation process aligns with the brand’s focus on a quality user experience. We tend to recommend products that are DIY friendly and if not, we suggest the necessary precautions to take and calculate how much it will cost to have the system up and running.

Click here to find out how we run installation tests.

Cost-of-ownership analysis

Water filtration systems, including some tankless reverse osmosis systems, tend to be costly investments for most households. Depending on the type of filter and water source, you may need to replace the filter media every six months, annually, or after a couple of years. You also need to factor in utility costs if your system runs on electricity, as well as water usage. We calculate the cost of ownership to help users choose a system that aligns with their budgets.

Check out how we conduct our cost-of-ownership analysis.

Warranty check

Given the high initial costs of some of these filters, a manufacturer must offer some form of assurance to cover the product in case it doesn’t work as intended. However, having a warranty does not equate to having a good warranty. We go through the warranty policies to find out what is truly covered and what is not covered. This step helps us recommend the products with the best warranties and money-back guarantees.

Here’s how we conduct warranty checks.

Customer service test

Customer service is one of the most important jobs in any company. It represents the personality of the company and the reason customers come back. We take our time to vet the customer service operations of these companies by asking questions about their customers’ experiences. Before we recommend any product, we make sure the manufacturer provides good customer support.

Learn more about how we run customer service tests.

Before You Buy a Tankless RO System: Understanding Contaminants in Your Water

Before you decide to purchase a tankless reverse osmosis system, and which system to purchase, it’s important to test your water source. Testing ensures you get a system that matches the contaminants present in your water.

According to Jess Goddard, a water quality engineer and one of our trusted partners at Tapscore, “Testing at least once every three years is suggested for utility water users. Water quality is dynamic and changes with engineering practices, regulations, and water sources impacted by a changing climate.”

Water testing is essential to safeguarding the health and safety of everyone in your household, even your pets. Different regions face distinct water quality challenges, with potential risks ranging from high levels of arsenic or lead to microbial contaminants. Testing helps homeowners identify any potential health hazards in their water supply, allowing them to prioritize the removal of specific contaminants that could pose health risks over time.

Common contaminants found in city water include chlorine, chloramines, heavy metals such as lead and copper, sediment, volatile organic compounds (VOCs), and various minerals. Tankless RO systems are designed to tackle these impurities through multiple stages of filtration, ensuring the elimination of particles, chemicals, and unwanted minerals. Chlorine and chloramines, commonly used in municipal water treatment, are effectively removed in the initial stages, improving taste and odor. Heavy metals and sediment are filtered out by the RO membrane, while additional stages may address specific contaminants depending on the system’s design.

As for well water, it often contains elevated levels of sediment, minerals, and contaminants that can adversely affect the performance and longevity of RO membranes. Sediment, iron, and manganese can clog the delicate pores of the RO membrane, reducing filtration efficiency and potentially causing damage. Additionally, high mineral content in well water, such as hardness ions, can lead to scaling issues on the membrane surface, affecting its ability to separate impurities. Furthermore, well water may harbor specific contaminants like bacteria, viruses, and agricultural runoff, which may not be effectively removed by standard RO systems. Pre-filtration, including sediment filters, carbon filters, and potentially UV sterilization, is crucial to addressing these challenges.

The Difference Between Tankless and Traditional RO Systems

A tankless reverse osmosis (RO) system is a water purification system designed to provide on-demand, continuous access to filtered water without the need for a storage tank. In contrast to traditional RO systems with storage tanks, tankless RO systems operate without a reservoir to store filtered water. Instead, they use a direct flow-through process, filtering water at the moment it’s requested, which eliminates the need for a storage tank.

The tankless design offers several advantages. First, it saves space under the sink, making installation more convenient, especially in kitchens with limited space. Second, it reduces the risk of secondary contamination that can occur in storage tanks, as water is not stored for extended periods. Third, tankless systems often feature higher flow rates, delivering filtered water more quickly, usually from the booster pump, which requires electricity.

You may have got stuck on that bit about “secondary contamination.” Let me explain. In a traditional RO system with a storage tank, water goes through the filtration process and is stored in a pressurized tank until needed. These systems are effective but may pose concerns related to potential contamination in the tank over time, and they can take up more space due to the presence of the storage tank.

But how does the storage tank get contaminated?

Over time, stagnant water in the tank can become a breeding ground for bacteria, algae, and other microorganisms. These contaminants can multiply and affect the quality of the stored water. Additionally, if the tank and its components are not properly sanitized during maintenance, biofilm — a thin layer of microorganisms and organic matter — can develop on the interior surfaces. This biofilm may harbor bacteria and impurities, leading to water quality issues. Moreover, contaminants from the air or the tank’s surroundings can find their way into the stored water.

The temperature conditions inside the tank can further exacerbate bacterial growth. Warmer temperatures can accelerate the multiplication of microorganisms, potentially compromising the purity of the stored water. Tankless RO systems eliminate the need for a storage tank, reducing the risk of contamination associated with stagnant water.

Both tankless and traditional RO systems employ similar filtration stages, including pre-filters, an RO membrane, and post-filters, to remove impurities and contaminants from the water. The key difference lies in the approach to water storage and delivery. Tankless systems provide a more direct and efficient solution for users seeking fast access to purified water without the drawbacks associated with storage tanks.

Back to product recommendations

Dive Deeper: In-Depth Water Filter Guides

We at Drinking Water are committed to providing you with the most up-to-date and thorough analysis of the water treatment industry. That’s why we’ve researched a wealth of topics and products for your review.

For more help deciding which water filter is right for your specific needs, check out the guides below:

Frequently Asked Questions

Is there anything better than reverse osmosis?

While reverse osmosis (RO) is highly effective in removing a wide range of contaminants, some alternative water filtration technologies may suit your needs better. The choice depends on specific water quality concerns. However, reverse osmosis is known for being the most comprehensive type of filtration, removing the most contaminants overall.

For information about filtration technologies, see our article about the nine types of water filters and when you should use them.

Which is better, tankless or tank RO?

The choice between a tank and tankless RO system depends on your personal preferences and requirements. A tank RO water system stores water for later use. It is convenient to get water, and if the water supply is turned off temporarily, water in the reverse osmosis tank can get you through it. However, it takes up space. Secondary pollutants stemming from the sealed pressure tank are also a concern. You must carefully consider these factors before buying this kind of RO filtration system. 

A tankless RO water system is much smaller and does not require a large amount of space under the kitchen sink. It does not have a storage tank, so the secondary pollution problem is eliminated. You can get refreshing water within seconds whenever you want. However, it is more expensive than an RO water system with a tank.

How much does a tankless reverse osmosis system cost?

The cost of a tankless reverse osmosis system varies based on brand, features, filtration capacity, and more. Generally, prices range from around $300 to $1,000, but can run even higher. Higher-priced models often come with advanced features like smart technology, increased filtration stages, and additional functions, such as remineralization or UV sterilization. It’s important to consider long-term costs, including filter replacement expenses. Additionally, installation costs may vary based on whether professional installation is required or if it’s a straightforward DIY setup.