7 Best Reverse Osmosis Systems of 2024

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Each year we thoroughly research and test a multitude of reverse osmosis systems to determine which are best. We’ve ranked the 7 systems on this list in terms of performance capability, efficiency, production rate, and of course, affordability.

Reverse osmosis is the most comprehensive at-home water purification solution, removing almost 100% of all dissolved solids – so it’s hands-down the best way you can protect your family from concerning drinking water contaminants. In fact, according to WebMD “Reverse osmosis units with carbon can remove nitrates and sodium as well as pesticides, fluoride, chloride, and petrochemicals.”

Chances are, you’ve never had to shop for anything like a reverse osmosis water filtration system before, and RO units are quite complex. There’s new lingo to learn, and with talk of efficiency ratios, GPD capacities, and rejection rates, you might feel that you’re in over your head. 

Luckily, we’ve done all the research for you and have outlined everything you need to know to simplify the buying process. We’ve explained why the shortlisted RO systems in this guide are our top picks, helping you to understand which features are the most important and what you should look for based on your own situation. 

There are several types of reverse osmosis systems available today, including under-sink and countertop systems, and whole-home options. To ensure you buy the best reverse osmosis system, know your budget, your water quality and TDS, the system’s capacity, efficiency ratio, certifications, and more. We’ve discussed our buying tips, as well as our own methodology for selecting the systems we’ve reviewed here, at the end of this guide.

🥇 Best Reverse Osmosis Systems

📊 Reverse Osmosis System Comparison Chart

SystemCloud RO
Cloud RO
Waterdrop G3 P800
Waterdrop G3 P800 Reverse Osmosis System
RKIN U1
RKIN U1
NU Aqua Efficiency Series
NU Aqua Efficiency Series
AquaTru
AquaTru countertop reverse osmosis water filtration system
Waterdrop K6
Waterdrop K6
Crystal Quest 1000CP
Crystal Quest 1000CP
Ranking1st2nd 3rd 4th5th6th7th
Ratings5/55/54.5/54.5/54.5/54.5/54/5
Price$750$999.00$749.95$625.95$449.00+ $799$478.16
Efficiency Ratio1:13:11:12:14:12:11:3
Stages of Filtration47544512
Production Rate80 GPD800 GPD75 GPD600 GPD~1 GPM600 GPD50 GPD
Certifications or TestingNSF 42, 53, 58NSF 58, 372NSF 58 (in progress)NSF 42, 53, 58, 401, P473NSF 58, 372
Annual Cost~$200~$145~$180~$155~$100$120~$120

🏷️ The Best Reverse Osmosis Filters in the News: The Latest Deals and Discounts

We’re constantly checking manufacturers’ websites and online marketplaces for the best deals for our shortlisted reverse osmosis systems. If we find anything worth sharing, such as a sale or discount that helps you to save money on your purchase, we’ll update the bullet list below with this information.

  • Save up to $130 on NU Aqua systems until May 28
  • Up to $600 off on select systems through May 28

⭐️ Reverse Osmosis System Reviews 2024

Specs

We’ve tested our fair share of tank-based reverse osmosis systems, including the more traditional systems that took up all our available under-sink space with their clunky designs. The Cloud RO is a much more refreshing take on these systems, with a cleaner, more compact and attractive appearance, while still offering all the benefits of a tank-based unit, including fast access to purified drinking water the moment you turn on the tap. 

The system has a sleek, modern design – it almost feels a shame that it’s designed to be installed out of sight underneath the kitchen sink. At the time of our review, it was priced at $750, and included with this purchase are all the initial filter stages, as well as a 2.8-gallon storage tank that delivers purified water on demand. The filters last up to 12 months (there are sensors on the unit that work out when the filters need replacing based on your water quality and consumption), and our estimated annual spend for filter changes was within $200. 

Best For

Folks looking for the smartest, most attractive, space-saving tank-based RO system, which has features that level up its performance and make it easier to use.

What We Like
  • Sleek, attractive design
  • Rejects up to 95% TDS
  • Tank-based design allows for faster access to purified water
  • Smart features and app connectivity for improved experience 
What We Don’t Like
  • Expensive – about twice the price of a traditional tank-based RO system
  • Not the best efficiency ratio we’ve seen
Cloud RO base with new filters installed

Superior RO Purification

Performance-wise, the general mechanics of the Cloud RO are similar to most of the other conventional RO systems we’ve reviewed. The system sends water through four stages of filtration: a carbon filter, an RO membrane, a sediment filter, and a coconut carbon remineralization filter (great to see this included rather than sold as an optional add-on at an extra cost, as with some of the other systems on this list). Combined, these filter stages reject up to 95% TDS and add healthy minerals back into the water, improving its taste. The list of contaminants that the system can remove is endless – a datasheet shared by the manufacturer lists 6 types of water disinfectants, 8 biologicals and particulates, 38 chemicals, 20 pesticides, 8 pharmaceuticals, 11 heavy metals, and 18 inorganic contaminants. The sediment and carbon filters have been third-party tested to NSF Standard 42, and the manufacturer told us that they’re in the process of getting the system officially performance certified to NSF Standard 58, for removing various contaminants with RO purification. 

If you’ve done some research into reverse osmosis, you’ll know that this water treatment process always results in water waste. The Cloud unit has a 1:1 efficiency ratio, which means it wastes 1 gallon of water for every 1 gallon purified. That’s one of the best we’ve seen for a conventional unit, especially given that the traditional system would waste 4 gallons of water per single gallon purified. 

A final important performance consideration for us was flow rate. The unit uses a non-electric permeate pump that speeds up water flow and maximizes efficiency, achieving about 80 gallons per day or 0.5-0.75 gallons per minute. Essentially, the faster the water flow through the RO membrane, the more water can be purified, and the less water is wasted. Plus, because the unit is tank-based, there’s always water ready to be supplied when you turn on the faucet.

Smart Design & Performance Features

There are a few other specific design and performance features that are unique to this system. To monitor important insights like the TDS and flow rate, the unit uses a long-lasting battery pack that powers the internal sensors. You get a new battery with a delivery of new filters, and you can return the used battery to the manufacturer to be recycled. It’s helpful that you don’t have to plug the unit into a power source, which is a bit tricky given that it’s designed to be installed under a kitchen sink. 

Like many of the more modern systems we’ve reviewed, the Cloud RO has app connectivity. The Cloud app gives access to helpful data including the incoming water quality, filter status, and percentage of minerals added back into the water. You can even track your tap water consumption, making it easier to stay hydrated. We were also impressed with the smart internal sensors, which report TDS data so you can see how effectively the filters are performing, and integrated pressure sensors that track your drinking water consumption and tank volume, using the data to improve the performance efficiency and water delivery speed.

Looking at the Cloud RO app on a smartphone

Read the Full Review: Cloud RO Review


Specs

How does this Waterdrop unit compare to our top pick, the Cloud RO? The most obvious difference is that the G3P800 is tankless, which means water must be purified through the RO filters before it can be delivered to the faucet. This gives the system space-saving benefits, and its 800-gallon-per-day flow rate (that’s 10x the Cloud RO’s 80 GPD flow) meant we never had to wait more than a few seconds for purified water to be available. Plus, the unit has a few unique features, including a built-in UV light and scale inhibitor, and its 1:3 efficiency ratio is the best we’ve ever seen in any POU RO system we’ve tested. 

What do all these benefits and features mean for the system’s price? When we got it for our review, it cost just under $1,000. Our projected annual spend on filter replacements (including 2 pre-filters, 1 post carbon block filter, and the RO membrane) was around $155. So yes, it is pretty expensive, especially given that it doesn’t use a tank, so it has fewer components overall. That said, we know from our own experience that you can’t find a better-value tankless RO system when it comes to reliable water purification and minimal water waste, helping to save money in the long term, so we think the unit is worth the upfront cost for anyone looking for the very best tankless reverse osmosis filter system available. 

Buying Tip: Sadly, there isn’t a post-remineralization filter included with this system – Waterdrop sells it separately at an extra cost. We recommend paying the extra $30 for this filter to add healthy, taste-enhancing minerals back to your RO water, which will otherwise taste a bit flat.
UpgradesPriceUses
Remineralization Filter$29.99Adding minerals back to water
Refrigerator Connector$32.99Connect RO system to refrigerator water line

Best For:

Anyone who’s looking for the very best of the best tankless reverse osmosis systems – and has the budget for a high-end product.

What We Like:
  • Slim, tankless, space-saving design (measuring just 5.67 inches across)
  • Excellent 800 GPD flow rate
  • Reduces 1,000+ harmful substances
  • Great 3:1 pure-to-wastewater ratio
Cons:
  • One of the most expensive POU systems
  • Remineralization costs extra
Waterdrop g3 p800 easy filter change

Modern, Efficient Tankless RO Performance

We know that many folks prefer tankless RO systems because they take up less space, but a problem we experienced when testing these systems was that the water flow from our faucet was very slow because we were having to wait for water to flow through all the RO filtration stages, rather than being delivered straight to the faucet via a pressurized storage tank. The G3P800 was pretty revelationary for us to test because it has the fastest water flow rate we’ve seen: 800 gallons per day. Waterdrop promises that you can fill a glass in under 6 seconds, and this was just about accurate for us – our average filling time was between 6.2 and 7.5 seconds.  

Flow rate aside, the unit’s 3:1 efficiency ratio was another performance feature that blew us away. We were reassured to know that only 1 gallon of our water was being wasted for every 3 gallons of water purified.

Important Note: Due to the G3P800 being a tankless unit, TDS creep is a possibility. This would reduce the total production rate number, meaning that the system wasn’t as efficient as is claimed.

Reduced 82% TDS

We were able to test the performance of the Waterdrop G3P800 first-hand by conducting a water analysis test on our tap water before and after filtering it through the system. Our results were as we’d expected for a reverse osmosis system: 82% of our TDS was reduced, from 84 mg/L to down to 15 mg/L.

waterdrop g3 p800 tds detection

We had fluoride, chloride, and lead in our water, which were all reduced by 100%.

Waterdrop g3 p800 arsenic and lead detection
Waterdrop g3 p800 fluoride and chloride detection

Plus, the system reduced 82% sodium, 90% barium, and more. Something to note is that the pH of our water decreased to 6.3 from 7.3, which is normal but not ideal – installing the alkaline remineralization filter should prevent this pH drop. 

Waterdrop g3 p800 sodium detection
Waterdrop g3 p800 barium detection

Like the Cloud RO, the G3P800 has a few unique features that support its overall performance, including the TDS meters on the smart faucet and the unit body, which helped us to keep an eye on the filters’ performance, and the built-in tracker that monitored filter life, saving us the hassle of making calendar reminders for filter changes. While other reverse osmosis systems remove some bacteria, but aren’t guaranteed to eliminate microorganisms, the G3P800 has a long-lasting UV purifier with a 99.9% sterilization rate, which gave us that extra assurance that our water was clean, safe, and microorganism-free. 

See our third-party laboratory testing data for Waterdrop G3P800 in the table below.

ContaminantMeasurementPre-InstallPost-Install% Change
Total Dissolved SolidsPPM8415-82.14%
ArsenicPPM0.00290-100.00%
BariumPPM0.02830.0033-88.34%
CalciumPPM20.22.6-87.13%
ChloridePPM2.20-100.00%
CopperPPM0.2030-100.00%
FluoridePPM0.30-100.00%
LeadPPM0.00080-100.00%
MagnesiumPPM2.130.27-87.32%
ManganesePPM0.00480-100.00%
Nitrate (as N)PPM1.10.1-90.91%
PotassiumPPM2.120-100.00%
SeleniumPPM0.00150-100.00%
SodiumPPM9.331.65-82.32%
StrontiumPPM0.1990.025-87.44%
SulfatePPM7.80-100.00%

Specs

The U1 is another recently manufactured RO system, and it boasts a few features that none of our top two recommend under-sink systems offered, including the option to select the purified water temperature, and hydrogen infusion (which we’ve explained in more detail later). As for how it compares speed and efficiency-wise, its 75 GPD water production rate is almost the same as the Cloud RO, and the 1:1 efficiency ratio is identical. 

The big perk of a countertop system like the U1 is that very little installation is required. Our unit arrived partially assembled, and we had it set up on our countertop and ready to go in a matter of minutes. At the time of our testing, the unit cost around $575 – so the most affordable on this list so far. Yes, the price is around $150-$250 more than some of the cheaper countertop RO systems, but we felt that the U1 was worth the spend because of its unique offerings that we simply couldn’t find elsewhere. We anticipated that we’d spend $100-$150 a year on filter replacements. 

UpgradesPrice
2-Year Filter Bundle$290
Turntable $260

Best For:

Folks looking for the most capable, feature-rich countertop RO system that purifies, remineralizes, and hydrogenates drinking water in one, then lets you access it at any temperature.

What We Like:
  • Removes up to 99% of all contaminants
  • IAPMO tested for contaminant removal
  • Remineralizes and hydrogenates water
  • No-install countertop setup
What We Don’t Like:
  • Quite expensive
  • Tanks must be filled/emptied frequently
Brian holding the RKIN U1 from end to end

Innovative Features

The RKIN U1 offers a water treatment process that stretches beyond the typical RO system. It begins with the filtration stages we’ve come to expect from reverse osmosis, including sediment and carbon filters, and an RO membrane. Beyond this stage is an alkaline post-filter (bonus points from us for the fact that this is included rather than being an optional add-on) and a hydrogen infusion filter (which we’ve previously only ever found on much more expensive systems). Our purified water had a negative ORP reading of 340, and although the research into hydrogen infusion in water is limited, we appreciated having access to the possible benefits of this treatment alongside the general health and safety benefits of purified, remineralized RO water. 

In terms of using the U1, it was another unit we tested that had a number of forward-thinking features to improve our own experience and the system’s performance. We found the smart display easy to use, and the various presets and custom water temperatures were a highlight for us. Being able to dispense hot water from the unit, rather than having to dispense it cold and heat or boil it ourselves, was a game-changer. As with the other top systems we reviewed, there was a filter life indicator that took the guesswork out of filter changes. One thing we did note, however, was that filling and emptying the tanks was a bit of a hassle. With this system not being connected to our waterline, and with no dedicated drain line, we had to fill the tank and empty the drain tank periodically throughout the day. We got into a routine with this, but it was an extra responsibility that we didn’t have to commit to with any of the under-sink systems we tested. 

Superior Water Filtration

We had the opportunity to test the U1 on our water supply in Steamboat Springs, CO, and our before-and-after water test results were telling. The unit reduced our water’s TDS by about 79.5%, from 112 to 23 mg/L.

Rkin u1 tds removal

It also reduced trace levels of lead, fluoride, uranium, zinc, copper, chloride, and molybdenum in our water by 100%. Our water tasted pure and clean, but with a nice mineral after-taste thanks to the post-remineralization. 

Rkin u1 copper, lead, uranium, and molybdenum reduction
Rkin u1 fluoride and zinc reduction using advanced city water test

We spoke to RKIN, who informed us that they’re currently in the process of obtaining an NSF certification for the U1, and it already has IAPMO testing for the reduction of TDS, fluoride, lead, PFOA and PFOS, and chromium 3 and chromium 6.

We’ve summarized the performance of RKIN U1 from our third-party laboratory analysis below.

ContaminantMeasurementPre-FiltrationPost-Filtration% Change
BariumPPM0.0140.0087-37.86%
CalciumPPM23.93.6-84.94%
ChloridePPM9.20-100.00%
CopperPPM0.05250-100.00%
FluoridePPM1.50-100.00%
LeadPPM0.00090-100.00%
MagnesiumPPM6.080.39-93.59%
MolybdenumPPM0.00470-100.00%
Nitrate (as N)PPM2.10.2-90.48%
PhosphorusPPM1.10-100.00%
SodiumPPM9.911.2-87.89%
StrontiumPPM0.1082.422140.74%
SulfatePPM7.61.6-78.95%
Total Dissolved SolidsPPM11223-79.46%
UraniumPPM0.01820-100.00%
ZincPPM0.5590-100.00%

Read the full review: RKIN U1 Countertop Reverse Osmosis System Review


Specs

In terms of build, function, and appearance, the NU Aqua Efficiency system doesn’t have many differences from the Waterdrop G3P800. The unit has a cube design that takes up slightly more floor space but isn’t as tall, and it’s another tankless offering, meaning that water is purified when you turn on the faucet, rather than being ready and waiting in a tank. 

If you like the idea of a tankless water filtration system but you want to spend less money upfront, this NU Aqua model might be better for you than the Waterdrop system. When we reviewed the system, it cost around $470, which makes it more than half the price of Waterdrop’s offering. Yes, the NU Aqua model has s slightly poorer 2:1 efficiency ratio (compared to the G3P800’s 3:1 efficiency) and a slower 600 GPD water delivery rate (versus the G3P800’s 800 GPD production rate), but those are only very minor differences that don’t significantly affect performance. Our estimated annual spend on maintenance and filter changes was pretty average at around $155. 

Best For:

Folks looking for a more affordable alternative to the Waterdrop G3P800 that still offers the same benefits of tankless under-sink reverse osmosis water purification. 

What We Like: 
  • More affordable than our top-pick under-sink system
  • Great 2:1 efficiency ratio
  • Easy to maintain
  • Good 600 GPD flow rate
What We Don’t Like: 
  • No included remineralization filter
  • Slower water purification rate than the Waterdrop system
NU aqua efficiency series in kitchen table

Four-Stage RO Filtration

The NU Aqua Efficiency filtration system offers four stages of reverse osmosis filtration: a PP/CB filter (which offers two stages of filtration in one), a granular activated carbon filter, and a semi-permeable reverse osmosis membrane. We were disappointed to see that, as with the Waterdrop G3P800, the unit doesn’t come with a built-in remineralization filter – NU Aqua sells one separately, which costs around $63 (twice the price of Waterdrop’s similar offering). As expected, the system can greatly reduce or remove a broad range of common contaminants, including VOCs, chlorine, rust, sediment, hardness, organic chemicals, heavy metals, and salts. 

Our only gripe with the system’s contaminant removal was that it isn’t NSF-certified yet, and we also couldn’t find third-party test results to tell us exactly which contaminants it had been tested to remove, and to what percentage. That doesn’t affect the performance of the filtration system in any way, but some people prefer the reassurance of an official certification.

Quick, Efficient Water Purification

We think the NU Aqua RO Tankless Reverse Osmosis System is another great choice if you want to minimize your water waste production. While the 2:1 pure-to-wastewater ratio isn’t quite as impressive as the Waterdrop G3P800’s 3:1 ratio, it’s still one of the very best we’ve seen. But there’s a risk of TDS creep, as we highlighted in our G3P800 review. 

As for water production rate, the NU Aqua unit has a 600-gallon-per-day capacity. That’s pretty fast, and the system’s booster pump helped to keep our water flow steady. The built-in noise isolators meant we didn’t hear any loud mechanical sounds while it was in operation or on the occasions when it sent the discharge water down the drain. That made a nice change from many of the conventional systems we’ve tried in the past, which were too noisy for our liking. Plus, the fact that the NU Aqua system doesn’t have a bulky storage tank meant we could save space, and we recommend it for folks with smaller under-sink cabinets. 

Read the full review: NU Aqua Platinum Series


Specs

Like the RKIN U1, the AquaTru is a countertop system, so all the filters are contained inside a single unit that sits on your kitchen countertop. When we got the AquaTru for testing, we could choose between a few different models: 

  • AquaTru Classic – the standard model 
  • AquaTru Connect – the Classic model but with WiFi connection, which tells you useful info on filter life, water usage, etc. on the app
  • AquaTru Alkaline Classic – the Classic model but with an alkalizing VOC filter rather than the standard VOC filter 
  • AquaTru Alkaline Connect – the Classic model with the two extra features listed above
AquaTru ConfigurationsInclusionsPrice
ClassicRO + VOC Filter$449
ConnectWifi RO + VOC Filter$499
Alkaline ClassicRO + Alkaline Boost VOC Filter$469
Alkaline ConnectWifi RO + Alkaline Boost VOC Filter$519

We went for the Alkaline Classic model, since it cost just $20 more than the AquaTru Classic and meant we could remineralize our water within the system itself, rather than having to worry about post-remineralization ourselves. At the time of our review, the upfront cost ranged from $450 to $520, depending on the system configuration. So it’s a slightly more affordable option than the U1, but there are a few features that the U1 has and the AquaTru doesn’t, like hot/cold water dispensing and hydrogen infusion. Our anticipated annual spend on maintenance was around $100.

Best For:

Anyone who prefers a slightly more affordable alternative to the RKIN U1 with a better efficiency ratio to minimize long-term wastewater production. 

What We Like:
  • Very good efficiency ratio of 4:1
  • IAMPO certified performance
  • Optional upgrades with remineralization and WiFi connection
  • Tracks filter lifespan & alerts you to filter changes
What We Don’t Like:
  • Remineralization upgrade costs extra
  • Needs to be filled/emptied manually
Brian pouring filtered water from Aquatru

IAPMO R&T Certified Water Purification

Going back to when we reviewed the RKIN U1, it was almost exactly what we were looking for – but it doesn’t yet have an official performance certification, and we knew that some folks would only feel comfortable buying a certified system. The AquaTru stood out to us because of its certified performance – it has been IAPMO certified to NSF Standards 42, 53, 401, and P473, for its ability to remove TDS, copper, fluoride, lead, chromium, barium, arsenic, radium, nitrate, nitrite, and more (82 contaminants in total). And when we tasted our purified RO water, it was all the proof we needed of the system’s performance – it was clean, fresh, and with a slight mineral crispness (remember, we bought the system with the remineralization VOC filter).  

Aquatru contaminants with possible health effects detection part 1
Aquatru contaminants with possible health effects detection part 2

Here’s a summary of the performance of AquaTru as assessed through our third-party laboratory analysis.

ContaminantMeasurementPre-FiltrationPost-Filtration% Change
BariumPPM0.0140-100.00%
CalciumPPM23.90.7-97.07%
ChloridePPM9.20-100.00%
CopperPPM0.05250-100.00%
FluoridePPM1.50-100.00%
LeadPPM0.00090-100.00%
MagnesiumPPM6.080.36-94.08%
MolybdenumPPM0.00470-100.00%
Nitrate (as N)PPM2.10-100.00%
PhosphorusPPM1.10-100.00%
SodiumPPM9.910-100.00%
StrontiumPPM0.1080-100.00%
SulfatePPM7.60-100.00%
Total Dissolved SolidsPPM11212-89.29%
UraniumPPM0.01820-100.00%
ZincPPM0.5590-100.00%

High Efficiency, Slower Water Delivery

Another major standout feature of the AquaTru RO system for us was its 4:1 performance efficiency. That’s better than any of the other countertop systems we’ve reviewed – and the RKIN U1’s 1:1 efficiency ratio simply doesn’t compare. The unit only wastes 1 gallon of water for every 4 gallons of clean, filtered water produced, so we didn’t have the guilt of wasting gallons of water every day. But, just the same as with the RKIN U1, we still had to manually fill the AquaTru’s tap water tank and empty the wastewater tank throughout the day because of its lack of connections to a water line. 

We weren’t as impressed with speed of water delivery compared to with the RKIN U1. While the purification speed was helped along by a booster pump, when it came to accessing the water, we had to be patient. Our purified water was stored in a pressurized gravity tank, and as the tank emptied, the flow of water from the dispenser would slow. 

Are there any other features of this RO water filtration system that we noted? Admittedly, from a tech perspective, it didn’t wow us like the RKIN U1. But we still had all the features we felt were needed in a modern countertop RO system, including the digital display screen, which gave us filter lifespan information and saved us the job of making our own calendar reminders for filter changes. Plus, we think some folks will appreciate upgrading to the WiFi Connect system, which means you can download a dedicated app and use it to track the lifespan of your filters, as well as your water quality and consumption. 

Read the full review: AquaTru Review


Specs

The K6 isn’t the only unit to offer hot water dispensing (the RKIN U1 also does), but a huge benefit of this system is that you get hot water at the touch of a button straight from a faucet. Like our top-pick Waterdrop G3P800 model, the K6 is a tankless under-sink system that gets plumbed into the cold water line beneath your kitchen sink. It’s pretty similar in design and appearance to the G3P800, but it uses just one filter cartridge, with a heating element above it.

Price-wise, the K6 is a bit cheaper than the G3P800, costing $600 with a discount code displayed on the page at the time of our review. From our comparison of the two units, we concluded that the K6 is the more affordable option because it doesn’t quite match up when it comes to filtration speed (600 GPD versus the G3P800’s 800 GPD rating) or efficiency ratio (2:1 versus the G3P800’s 3:1 ratio). But this system is still a lot better in these categories than most of the other under-sink RO units we’ve tested. And with just one filter to replace, the K6 is the easier of the two Waterdrop units to maintain – knowing that the filter lasted up to 1 year, our estimated annual spend was around $120 (the price per replacement filter cartridge). 

Buying Tip: Like the Waterdrop G3P800, the K6 doesn’t come with a remineralization filter, but you can buy one from Waterdrop separately. We recommend doing this because RO water lacks healthy minerals and usually tastes pretty flat. 
UpgradePriceUses
Remineralization Filter$29.99Adding minerals back to water

Best For:

Folks who want a performance-certified under-sink RO system that can filter and heat their water for them, then deliver it straight to their faucet. 

What We Like:
  • NSF certified performance
  • Purified water at any temperature
  • Under-sink on-demand filtration
  • Only 1 filter to replace
What We Don’t Like: 
  • Flow rate & efficiency ratio aren’t as good as the G3P800
  • Remineralization post-filter costs extra

Dispenses Hot RO Purified Water On Demand

The Waterdrop K6’s ability to produce heated RO water was the main performance benefit for us. Most under-sink RO systems we’ve tested can only deliver cold RO water because they’re connected to the cold water line. You can’t try and cheat the system by connecting the unit to your hot water pipe instead because hot water could damage the filters. Plus, then you’d only get access to hot RO water, not cold. Heating the water post-purification is the answer, and the K6 makes it possible with its built-in heating element. The included smart faucet has arrow buttons that you can use to adjust the temperature of the water from 104°F to 203°F. It also displays the TDS of the filtered water so you can check the filter is working as intended. For the safety conscious, and especially for families with children, we noted all the safety features you’d expect from a hot water dispenser, including a heating overtime protection function and child lock.

5-Stage Reverse Osmosis Treatment

How does this reverse osmosis system work? The K6 packs 5 RO filtration stages into a single filter carriage: a semi-permeable reverse osmosis membrane, two PP cotton stages, a carbon block filter, and a carbon fiber filter. Combined, these remove chlorine, fluoride, arsenic, chromium, heavy metals, salt, and more. Sadly, the unit doesn’t yet have an official performance certification (we contacted Waterdrop about this to be sure). However, the customer rep we talked to said that the K6 contains the same semi-permeable membrane as Waterdrop’s NSF certified systems, which is reassuring to know.

In terms of water production rate, a 600 GPD rating isn’t the best we’ve seen – but it’s still pretty great for a tankless system. Waterdrop says you can fill a glass in 6 seconds, but for us, the filling time was more like 8-10 seconds


Specs

This 12-stage RO water filter provides every type of water filtration imaginable, including add-on filters. At the time of our review, we noted 6 different optional add-ons for the system, including dedicated filter stages for nitrate, arsenic, and fluoride removal, and ionization and remineralization, as well as an optional brushed nickel faucet and leak detector smart valve. But whether you choose any of these add-ons or not, the main 12-stage RO process remains the same, including carbon and sediment filtration, ultrafiltration, ion exchange, a redox media, an RO membrane, and more. 

Given just how many stages of filtration are included in the base model alone, we were impressed with the $478 system price tag. Yes, the water production rate and efficiency ratio are less impressive than the other systems we reviewed for this guide, but if contaminant removal is the factor you care about the most, the Crystal Quest system should tick your boxes. Of course, things can get pricier if you choose to add a dedicated filter stage or any of the other upgrades, which add around $20-$70 per add-on to the upfront cost. It was difficult for us to calculate annual maintenance cost since this depends on which upgrades (if any) you choose, but for the main unit alone, we estimated a spend of around $120.  

UpgradesPriceUses
Nitrate Filter Cartridge$59Nitrate removal/reduction
Arsenic Filter Cartridge$69Arsenic removal/reduction
Fluoride Filter Cartridge$67Fluoride removal/reduction
Ionizer, Mineralizer and Oxidation Cartridge$69Adding minerals back to water
Brushed Nickel Faucet$19.95Prevent dirty drain water from flowing back to drinking water
Leak Detector Smart Valve$59.50Water leak detection

Best For:

Anyone looking for a thorough, customizable RO filter that they can build to suit their own water filtration needs.

What We Like: 
  • Comprehensive 12-stage RO process
  • Great value for money
  • Optional filter add-ons
  • Good storage tank capacity
What We Don’t Like: 
  • Bigger and bulkier than other under-sink systems
  • Not as efficient as our other top picks

Thorough RO Purification

We know that most folks opt for reverse osmosis because they know it’s the most comprehensive water treatment solution to ensure the removal of the majority of dissolved solids. The Crystal Quest system proved to be one of the most thorough RO purification systems we’d reviewed, packing an impressive 12 stages of filtration into a single system, including solid carbon, ultrafiltration, micron filter pads, granular activated carbon, ion exchange, oxidation/reduction, and reverse osmosis. With these filtration stages alone, this RO system can remove a range of contaminants, including VOCs, microbes, sediment, chlorine, and heavy metals. We’ve never before come across a system that uses both ultrafiltration and reverse osmosis within the same unit – it’s usually a case of one or the other. Our only disappointment was that the system doesn’t appear to have any performance certifications or even test results viewable online. 

As if 12 stages of filtration weren’t enough, the Crystal Quest Under Sink Water Filter comes with add-on filters (at an extra cost), including nitrate, arsenic, and fluoride filters. While reverse osmosis targets these contaminants anyway, if you have very elevated levels or you’re specifically concerned about any of them, adding a dedicated filter stage for the contaminant in question should offer extra reassurance that you’re targeting it as thoroughly as you can. Even if you think no other add-ons are necessary, we recommend the ionizer, mineralizer, and oxidation cartridge to remineralize your RO water, improving its taste and health properties.  

A couple of final notes on the Crystal Quest system’s performance: it has a 50 GPD water production rate, which is second place to our top tank-based under-sink system, the Cloud RO system (which has an 80 GPD production rate). We don’t think production rate is something to be too concerned about with a tank-based unit because filtered water is stored in a tank and delivered under pressure to your faucet whenever you need it, so there’s no waiting around for the filtration process unless you need to use a lot of water all at once. The Crystal Quest system has a 3.2-gallon stainless steel tank, which is a good size for most families. The pure-to-wastewater ratio is 1:3, which is typical for a conventional system, but the system is definitely lacking efficiency-wise compared to the other systems we’ve reviewed. Unfortunately, that means more water waste – a side-effect of a more traditional tank-based unit like this one. 


🧾 Buyer’s Guide – How to Select the Best Reverse Osmosis System

The best reverse osmosis system for you depends on your budget, contaminant removal goals, and other desired outcomes. Make sure to consider all the factors that could influence your purchasing decision before you start shopping. 

Here, we’ve shared everything we personally considered – which you will also find helpful to consider – when deciding on the best reverse osmosis filtration system for different situations.

  • Contaminants in source water – First, we considered the contaminants in our source water. We know from regular testing that our water contains trace levels of fluoride, lead, nitrate, disinfection byproducts, minerals and salts, and other impurities. Our advice is to test your water to find out what it contains and what you want to remove. Generally, the greater the total dissolved solids concentration, the faster the filters will become clogged. Plus, an excess of certain minerals, like hardness ions and iron, might damage the RO membrane. We generally only review RO systems for city water, but if you’re on a private well and want to benefit from RO purification, our advice is to install suitable pre-filtration (such as sediment or iron filters, or water softeners) upstream of the reverse osmosis system.  
  • System type – We identified four key types of reverse osmosis water filters: tank-based under-sink systems, tankless under-sink systems, countertop systems, and whole-home systems. Of these system types, we reviewed the first three. We’ve made a separate guide for whole-house RO systems since there are specific factors that only apply to these units. 
  • Efficiency ratio – We also considered the efficiency ratio of the systems we were reviewing, or the gallons of water that were wasted for every gallon purified. Conventional RO systems generally waste 3-4 gallons of water for every 1 gallon purified, but we determined that many of the modern systems have much better efficiency ratios of 1:1 gallons to 4:1 gallons, meaning that only one gallon of water is wasted for every 1-4 gallons of water purified. 
  • Water usage – This was something that we considered when reviewing the countertop and tank-based systems in particular. Our aim was to find systems that would offer a practical, convenient solution for the average family of 2-4. We found that using more water than average might have effects on the system. For instance, a tank-based system stores drinking water to be delivered to your faucet, and using too much water at once could empty the storage tank. If your RO water requirements are a lot higher than the average family’s, we recommend a tankless under-sink water filtration system that delivers purified water on demand, rather than a countertop unit with tanks that you’ll need to empty and fill constantly. 
  • Water pressure – In our research, we found that the reverse osmosis process can only work effectively when enough pressure is applied to force the water through the semi-permeable membrane (the RO filter) to the other side. Water pressure isn’t an issue with countertop systems, which use an electric pump to send water through the system. But for under-sink reverse osmosis filters, most manufacturers say that your water pressure should be at least 60 PSI for optimal functioning. We strongly advise installing a pressure booster pump if your water pressure is lower than this. 
  • Storage capacity – For RO systems with a storage tank (both tank-based under-sink systems and countertop systems), storage capacity was something else for us to compare and consider. We found that most under-sink systems had a storage tank of around 1.5-3 gallons, while the countertop systems could hold around 0.5-0.75 gallons of filtered water. 
  • Remineralization needs – We knew that reverse osmosis, being the most thorough water treatment process, removed everything from water, including healthy minerals and salts. While we can get magnesium and calcium from other sources, obtaining them through drinking water is an easy way to ensure we’re getting our daily mineral requirements. When choosing the systems for this guide, we looked for those with a built-in remineralization filter or at least an optional add-on filter, allowing for minerals to be added back into the filtered water before dispensing.

✅ 3 Specific Reverse Osmosis System Buying Guides

🔎 How We Determined Which Reverse Osmosis Water Filtration System Is Best

There were a few things that we wanted to learn before we even began our reviews process. First, we wanted to be certain that reverse osmosis was a suitable water treatment solution, and we were keen to learn more about how the RO process could be the right choice for specific circumstances.

In this section, we’ve discussed our research into water quality and reverse osmosis systems, the steps we took when shopping for the best RO systems, the advantages of this method of water treatment, and more.

🤔 Why Buy A Reverse Osmosis Water Filter?

First, we wanted to know why we, or anybody else, should invest in a reverse osmosis water filter. 

To learn this, we researched water quality data to understand how our drinking water might be impacted by common contaminants in the US.  

Water Quality Facts and Figures

In our research, we came across a number of studies that supported our belief that water purification could be beneficial to the average US homeowner on a city drinking water supply. Some of the most notable studies were:  

  • A USGS study, which found that just under half of the nation’s tap water was contaminated with at least one type of PFAS chemical. PFAS are a group of synthetic chemicals with several known health effects, including cancer. 
  • An NRDC analysis, which found detectable lead levels in over half of the US population’s water supplies in the 2018-2020 period.
  • A Consumer Reports investigation, conducted with The Guardian, which discovered “alarming” levels of PFAS, lead, and arsenic in water samples obtained from municipal supplies across the US.

The research and data confirmed to us that water quality is something to be concerned about in the US, despite how our local water utilities may try to assure us otherwise. The reality is that many of the contaminants in our drinking water aren’t regulated, and organizations like the Environmental Working Group argue that the regulations that are in place simply aren’t strict enough to protect public health. Plus, contaminants like lead and other heavy metals may enter our drinking water supplies after filtration at the treatment plant. Since we can’t rely on our local authorities to keep us safe from these impurities, at-home water treatment is the best alternative. 

Why is reverse osmosis particularly beneficial for removing contaminants? This water purification method is more thorough and comprehensive than non-RO water filtration, with numerous studies documenting its ability to effectively remove a range of contaminants, including: 

We concluded that reverse osmosis was one of the most reliable solutions for removing the majority of drinking water contaminants, and was a good choice for people who preferred to spend more money upfront on the most comprehensive treatment option.

Closer look of the reverse osmosis membrane

👍 Top 5 Advantages Of Reverse Osmosis Filter Systems

A reverse osmosis water filtration system boasts a number of benefits that set it apart from alternative water treatment methods. Based on our own experience testing and reviewing reverse osmosis filters for this guide, we identified the following advantages of these systems:

  • Very thorough contaminant removal: The RO process can remove the majority of impurities and pollutants, including chlorine, pesticides, nitrates, bacteria, fluoride, pharmaceuticals, lead, PFAS, and arsenic. Reverse osmosis is more thorough than any other filtration method because it uses a semi-permeable membrane, with tiny pores that reject contaminants as small as microorganisms. 
  • Improve water quality and safety: By removing the majority of TDS, an RO system can significantly improve the quality of your water and eliminate the safety concerns associated with certain trace contaminants. 
  • Easy to maintain: A reverse osmosis water filtration system is fairly simple in design, so you won’t need to worry about taking everything apart for a stringent regular cleaning process. There are usually 2-4 filters to replace, but this is easy to do and only required every 6-24 months on most modern systems.
  • Cost-effective: While RO systems are more expensive than other filter types, when you compare their performance to these alternative options, the cost is more than worth it. With a reverse osmosis system, you’ll no longer need to spend money on filtered water from the supermarket, so the unit should pay for itself within a few years. 
  • Upgrades & smart features available: Many of the modern reverse osmosis systems we’ve reviewed today have numerous built-in smart features, like TDS and filter life monitoring, remineralization, and hot and cold water dispensing.

🛒 How to Buy

There were four key steps we took when selecting the best reverse osmosis system for our needs. We advise you to also take these steps to ensure you make the best decision based on your situation.  Before we started shopping, we:

  • Considered what we were looking for filtration-wise: Our first step was to decide exactly how we wanted to treat our drinking water. We knew that the best reverse osmosis systems could remove almost all contaminants, but some could provide more thorough purification and higher TDS removal than others. Some systems also offered additional treatment, like ultrafiltration and UV light purification. We’ve made this water quality testing guide for folks who want to find out what their drinking water contains, so they can double-check in advance that an RO system can remove their problem impurities. 
  • Noted the features we wanted: Next, we listed all the essential features in our reverse osmosis system of choice. For instance, remineralization was a must for us, so we looked for RO systems that either had a built-in remineralization filter or came with an optional remineralization. Knowing exactly what we wanted upfront enabled us to shop more mindfully, with a reduced likelihood of being convinced into an unnecessary purchase. 
  • Set a pre-determined budget: We didn’t want to overspend on a reverse osmosis system, so, once we’d researched all the best systems, we calculated the average price ranges for each category, including maintenance costs. From there, we set a budget and tried to stick to it. If we were ever considering spending more money upfront, we asked ourselves whether the system’s features made it worthier of its higher price tag. 
  • Look out for discounts and deals: Finally, we looked for all the available deals and discounts we could find for our chosen reverse osmosis systems. We identified that most of the brands we’d reviewed offered seasonal discounts and sales, so if you can wait around for a shopping event, we recommend doing so. It’s a great way to get your chosen system at a fraction of the price. 

📚 Methodology: How We Tested RO Systems

There were a few different ranking factors we used when testing the reverse osmosis systems in this guide. 

Quality of Components

First, we assessed the quality of the components, including the filters themselves, in the RO systems we were testing. We wanted to know how these components felt, what they were made of, and how they affected the system’s performance. We noted that reverse osmosis systems with poorer-quality parts were less durable and unlikely to last as long as anticipated. Poorer-quality filters had a shorter lifespan and required more maintenance and upkeep.

Filter Performance 

We also considered filter performance when shortlisting the best RO systems. We tested and reviewed dozens of RO water filters to get an understanding of what we could expect performance-wise across several different categories: 

  • Water production rate
  • Efficiency ratio
  • Contaminants removed (including TDS removal)

Once we’d determined the average figures for these categories, we could compare a specific system’s performance and see if it was above or below average in each category. 

Under sink reverse osmosis system

Price

Price was another ranking factor that helped us to shortlist the filtration systems in this guide. We noted the cost of the system upfront, including any add-on or upgrade costs (when essential for us, such as remineralization), then prioritized the best-value systems based on their price and features. 

Maintenance Requirements

Next, we considered a reverse osmosis system’s maintenance requirements and how this affected its overall value for money. We know that RO water filters are a little more maintenance-heavy, but we included some lower-maintenance options (such as systems that combined multiple RO stages into just one or two filter cartridges) and looked for units with long filter lifespans to limit the frequency of changing the filters.

reverse osmosis system replacement filters

Company Reputation & Customer Reviews

Finally, we wanted to gather information beyond our own experience when determining the suitability of the RO water filters for this list. We read customer reviews on websites like Amazon, which helped us to learn the general customer experience with specific products, as well as gave us insight into how the systems performed with long-term use. Overall, we wanted to determine the reputability of various manufacturers based on customer feedback. 

❔ Frequently Asked Questions

How much does a reverse osmosis system cost to install?

If you choose to install a reverse osmosis system yourself, there should be no extra cost to install (aside from possibly the cost of a few plumbing supplies, depending on your under-sink plumbing situation). If you choose to hire a plumber to handle the installation process, the cost to do so is usually between $100 and $350, depending on the complexity of the job.

How long does a reverse osmosis system last?

A reverse osmosis system generally lasts 10+ years with proper care and maintenance. During this time, you might need to replace parts every year or two, such as your filters, o-rings, and any moving parts. 

How much wastewater do reverse osmosis systems produce?

Conventional reverse osmosis water filters waste around 4 gallons of water for every 1 gallon purified. The good news is that newer RO water filters are far less wasteful – they typically only waste 1 gallon for every 1-4 gallons purified. 

What is the best reverse osmosis system out there?

In our opinion, the best reverse osmosis system that currently exists is the RKIN U1, because it offers high-quality RO purification along with a host of unique features that we’ve not found collectively on any other system, including hot and cold water dispensing, remineralization, and hydrogen infusion. However, the best system for you ultimately depends on your budget and needs. 

What kind of reverse osmosis system is best?

The kind of reverse osmosis system that’s best depends on your personal preferences and situation. For instance, you might prefer a conventional tank-based under-sink system with a storage tank if you want instant access to filtered water when you turn on the tap. Or, if you want to save space, you might opt for a tankless under-sink system. Alternatively, if you don’t want the hassle of an install, you can go for a countertop RO system.

🤓 About Our Experts

Brian Campbell, WaterFilterGuru.com’s Founder and Water Filter Specialist, and Laura Schallcross, Senior Editor, researched, tested, and reviewed the reverse osmosis systems featured here. Check out their author bios below.

  • Brian Campbell
    President & CEO, CWS, CWR

    Brian Campbell, a WQA Certified Water Specialist (CWS) and Certified Water Treatment Representative (CWR) with 5+ years of experience, helps homeowners navigate the world of water treatment. After honing his skills at Hach Company, he founded his business to empower homeowners with the knowledge and tools to achieve safe, healthy water. Brian's tested countless devices, from simple pitchers to complex systems, helping his readers find the perfect fit for their unique needs.

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