Best Tankless Reverse Osmosis Systems of 2022

The Long Version

Reverse Osmosis (RO) may sound like some terrible band name, or drag you straight back to your chemistry lessons, but if you're after purified water, this filtration process offers unparalleled performance.

Through a series of stages, pressurized water is forced through a semi-permeable membrane that nasty heavy metals and contaminants simply cannot penetrate.

The efficiency of the process can vary depending on the membrane, water pressure, water temperature and other factors. But in most settings an RO system removes up to 99% of countless impurities, including lead, fluoride, chlorine, nitrates, sulfates and arsenic... making reverse osmosis one of the best ways to get truly “pure” water!

So perhaps you’ve made the leap and decided that an RO system is something you want for your house. Assuming that you’re planning to install an “under the counter” system – i.e. you want pure water on tap – then you’ll still need to decide whether you’re wanting to go tankless or not.

Traditional RO systems filter water slowly, so to make sure they have pure water available they store the filtered water in a large pressurized tank. But that can mean both a bulky tank that has to live somewhere under your counter, and water that sits and goes “stale” if not used… not ideal!

Tankless RO systems on the other hand use higher pressure and superior flow rates to filter water on demand. This allows owners to have pure water whenever they want, but avoid the need for a bulky storage tank. Plus, with water tanks there is always the risk of bacterial growth, so tankless RO systems prove superior in cleanliness too.

In this review we’ve rounded up the best tankless reverse osmosis systems, each leading in their respective categories. Much like the purification process itself, the undesirables haven’t made it through, leaving us with just top-quality products that actually work. Here we go!

Best Overall: iSpring RO500

PURIFICATION STAGES: 3-stage

OUTPUT: 500 gallons per day

DRAIN RATIO: 2:1

PRICE: $$$

PROS: Eliminates over 1,000 impurities; impressive 2:1 drain ratio; tool-free filter replacement; smart faucet shows TDS; vertical design saves space; compatible with ice maker

CONS: Must use included chrome smart faucet; first stage filter may require replacing in less than 12 months

For effective household water purification, it’s hard to find anything better than the iSpring RO500. There are a plethora of features that enable users to accurately and effortlessly track the quality of their water (TDS), as well as the status of their filters. Meanwhile, a game-changing 2:1 drain ratio will drastically cut the water waste you’d experience with less capable reverse osmosis systems.

The heart of the iSpring RO500 is the 3-stage filtration process. First, a multi-layered composite filter tackles sand, dirt and rust particles, as well as any chlorine. Next, a high-flow RO membrane comfortably removes over 1,000 contaminants, such as lead (98%), fluoride, arsenic, sodium and nitrates. Finally, a carbon block (CB) filter effectively ‘polishes’ the water, so no bad tastes or odors remain. The end result? Delicious, clean water!

Aside from keeping an eye on the TDS in your water, it is also able to show troubleshooting codes if issues arise. However, with smart leakage protection and filter replacement schedules, it’s unlikely that anything significant will slow you down.

A sleek, vertical design offers not only great aesthetic, but also takes up less under-sink storage space. Despite the compact size, it still pumps out a very admirable 500 gallons per day, or 0.4 gallons per minute. It’s pure functionality in pretty packaging, something that you can really raise a glass to!

Best for Efficiency: NU Aqua Efficiency Series Tankless 600 GPD

PURIFICATION STAGES: 5-stage

OUTPUT: 600 gallons per day

DRAIN RATIO: 2:1

PRICE: $$$

PROS: Extremely efficient 2:1 drain ratio without sacrificing output; very compact thus suitable for most sinks; quick installation; 5-year warranty

CONS: Flimsy faucet cord; power block separate from main housing

If water consumption concerns you, the NU Aqua Efficiency Series Tankless 600 GPD is unmatched for efficiency. While many competing models have no issue wasting 3 gallons of water (or sometimes as much as 4) to arrive at 1 gallon of pure water, the NU Aqua Efficiency Series gives you TWO gallons of pure, with only a single gallon wasted.

With such astounding efficiency, you may be wondering how well the NU Aqua purifies your drinking water. Well, this 5-stage RO system removes over 1,000 different contaminants. It features a polypropylene (PP) and carbon block (CB) combination filter for removing dirt, sand and rust, as well as chlorine and odors. After these pre-filters have done their job, the RO membrane eliminates everything else, such as heavy metals, nitrates, sulfates and fluoride.

The reverse osmosis membrane has an impressive lifespan of 36 months, though the pre and post-filters will need to be changed every 6 to 12 months, depending on specific usage and water condition.

With efficiency and purity expertly dealt with, the NU Aqua Efficiency Series Tankless 600 GPD throws in a brilliant ensemble of functional features. This includes the integrated silent booster pump that ensures the system can work with lower water pressures, and the smart faucet that indicates when the front-facing filters must be changed (which takes literally seconds).

Best for Ease of Use: Waterdrop G3

PURIFICATION STAGES: 7-stage

OUTPUT: 400 gallons per day

DRAIN RATIO: 1:1

PRICE: $$$

PROS: NSF 58 and 372 certified; tons of features aimed to improve user convenience; plenty of in-built safety elements that preserve components; real-time water quality (TDS) reading

CONS: Requires electricity to function; sits at a slightly higher TDS (15-40ppm) than other models; operating noise of 65dB

The Waterdrop G3 aims to deliver pure, tasty drinking water in as convenient a means as possible.

With an output of 400 GPD, this 7-stage filtration system utilizes pre and post filters with a 0.0001μm filtration rating RO membrane, removing 1000+ contaminants. Aside from impressive purification, the product seems to genuinely want to make your life easier.

Your filters will of course need changing, though the smart faucet will use three colours to continually notify you of filter status. When the lights turn red and you need to swap out filters, you can get at them easily with front panel twist-knobs. Real-time TDS readings help you feel like quite the scientist, knowing precisely how pure your water is at any given moment.

There is also a large range of in-built safety features. Firstly, there is much-needed leakage protection, but the Waterdrop G3 also boasts more comprehensive functions. If you forget to turn off a faucet, the overworking protection will kick in, stopping water dispensing to preserve the pump. Improper start-stop protection will also keep components working if the unit is operated incorrectly.

There is also automatic flushing after prolonged operation, designed to extend the longevity of filters. After 24 hours of no usage, the Waterdrop G3 will again flush the system, effectively a kind of integrated holiday mode.

Best for Alkalizing: Frizzlife PD600-TAM3

PURIFICATION STAGES: 7-stage

OUTPUT: 600 gallons per day

DRAIN RATIO: 1:1.5

PRICE: $$

PROS: 10 seconds to fill a 330ml glass; TDS readings remain low after remineralization

CONS: Requires an outlet so cannot work during power outages; included faucet is a little flimsy

Conventional reverse osmosis systems leave water slightly acidic. Although they are great at eliminating contaminants, they take out many natural minerals too.

The appeal of the Frizzlife PD600-TAM3 is that the third stage filter will alkalize the water, adjusting the PH to 7.5-9, while restoring natural minerals. This makes the water taste great, and it is also considered to be healthier.

Some reverse osmosis systems that feature a final mineralization process can get a little crazy, reintroducing an unnecessary amount into pure water. The Frizzlife PD600-TAM3 holds a TDS of around 20ppm, which you can conveniently monitor with the TDS reader. You may achieve lower TDS with other products, though extremely low TDS can have a negative impact on taste.

There’s a coconut shell carbon block (CB) filter, an RO membrane and a TAM3 alkaline remineralization filter. Interestingly, they don’t opt for the standard all-in-one filter housing, meaning you only need to change the filter cartridge. You don’t need to throw away the plastic shells, a nifty feature for the environmentally conscious.

Best for Versatility: iSpring RCS5T

PURIFICATION STAGES: 5-stage

OUTPUT: 500 gallons per day

DRAIN RATIO: 1:1

PRICE: $$$$

PROS: Commercial power for high demand; faster dual-direction filtering; automatic flushing; incredibly versatile tank options

CONS: Booster pump requires a power source; may be too much for smaller households

The iSpring RCS5T 500 GPD offers superior performance to the power-hungry, largely because it’s been designed with light commercial spaces in mind. Despite that, it still presents as a versatile choice for larger households, a remarkably capable tankless system!

The patented Side-Flow™ membrane can take in water from dual directions thus working faster than traditional products. The impressive work-rate adds up to 500 gallons a day. A high-power not only means you can use it with water pressures as low as 25 psi (1.7 bar), but also maintain a 1:1 drain ratio.

The 5-stage purification process, including their patented RO membrane with a pore size of 0.0001 micron, removes 99% of impurities. If you’re wanting serious cleanliness, you’ll enjoy having a polypropylene (PP), granular activated carbon (GAC), carbon block (CB) and post carbon filters. It’s an absolute beast!

Although the iSpring RCS5T 500 GPD system is tankless, you do have many options to add pressurized tanks for even greater performance. The smallest tank holds 0.5-3 gallons, which can be accommodated in most cabinets. However, if you’re so inclined, the iSpring RCS5T 500 GPD will gladly work with much larger storage tanks to supply pure water to an entire household.

Best for Smart Functionality: Purlette PL400G

PURIFICATION STAGES: 5-stage (dual filter)

OUTPUT: 400 gallons per day

DRAIN RATIO: 1.5:1

PRICE: $$

PROS: NSF 58 and 372 certified; system only uses 3 filters every 2 years; mobile app means stress-free maintenance; impressive drain ratio of 1.5:1

CONS: Designed for TDS <500, so cannot purify untreated well water; mobile app a little unstable

Although the reverse osmosis process is not at all new – traceable to eighteen century French physicist Jean-Antoine Nollet – it’s always nice to take advantage of modern tech.

The Purlette PL400G will absolutely purify your water, removing 99% of total dissolved solids (TDS), including heavy metals and chlorine. However, it works best if you embrace a truly futuristic style!

Not only does this unit have real-time TDS and filter status readings, there’s also an accompanying mobile app (Android, iOS) for effortless monitoring. You can check current water quality and the precise condition of your filter, even ordering replacements straight through the app. They recommend you replace the hybrid filter every 12 months and the RO filter every 24 months.

Aside from that, unique features like the energy-saving mode will put your RO system in hibernation mode after 3 hours of inactivity, extending the longevity of various components. Likewise, after 2 hours of constant usage, the device will automatically shut-off. As usual, there is leak protection, which preserves components by cutting off water supply.

The Purlette PL400G is even compatible with voice technology, meaning you can get all that information by simply talking to a compatible device, like Alexa. If you are tech-mad, it’s the obvious choice!

Best for Space Saving: GreatWell ROG400

PURIFICATION STAGES: Something

OUTPUT: 400 gallons per day

DRAIN RATIO: 1.5:1

PRICE: $$$

PROS: Assembled in the US, with US-based technical support; looks fantastic; incredibly compact design for many applications; affordable filters

CONS: Designed to work with portable water supply only; does not mineralize water; may take a minute or so for TDS to drop

If you think having a small under-sink area is reason enough to miss out on fresh drinking water, think again! The GreatWell ROG400 measures in at only L27.9 x W20.3 x H38.1, meaning you can conveniently store it in the most challenging of spaces. When compared to horizontal alignments, this vertical design saves significantly more space.

It’s a shame that this RO system will spend life out of view, though. Finished in a very attractive and sophisticated gold, it wouldn’t look out of place on a countertop. Aside from aesthetics, the GreatWell ROG400 has an impressive 1.5:1 drain ratio, as well as a 3-stage purification process that removes 99% of over 1,000 contaminants, including arsenic, calcium, lead and fluoride.

Although manufactured in Taiwan, it’s all assembled in the US, supporting their commitment to premium components. Indeed, all of the applicable components meet the NSF 58 requirements. The 3-in-1 PAC composite filter consists of 2 sediment filters and a carbon filter, effectively eliminating sand, dirt, rust, chlorine and odor from the water before it is passed through the RO membrane.

The built-in booster pump can increase water flow to as much as 0.53 gallons per minute, more than fast enough for typical household consumption. Filter change indicators and a leak-free water route make maintenance as easy as the installation.

Best for Small Households: Waterdrop M5

PURIFICATION STAGES: 5-stage (single filter)

OUTPUT: 50 gallons per day

DRAIN RATIO: 1:1.5

PRICE: $

PROS: Simple design thus easier maintenance; 1000+ contaminants removed; comes with a 80oz water pitcher

CONS: Very basic; no automatic flushing function; limited output

If you’re looking for pure water with minimal hassle, the Waterdrop M5 is the simple yet elegant solution. Requiring no electricity or pump, the device sits comfortably on a countertop while gradually filling the portable BPA-free Tritan plastic 80oz pitcher.

The all-in-one filter has five layers, two polypropylene (PP) cotton layers, an activated carbon fiber, an RO membrane (pore size of 0.0001μm) and a post-activated carbon block layer. You can say goodbye to over 1,000 different contaminants, including heavy metals, chloramine and residual chemicals in tap water. The filter is rated for 550 gallons, or 12 months of use, making it ideal for smaller households with lower occupancy.

As no plug is required, you are entirely free to position the Waterdrop M5 wherever best suits you. At the same time, no pump means no noise, keeping the kitchen quiet and relaxing. The sleek silver design will seamlessly fit into any space, meaning you only need worry about quality water whenever you want it.