We’ve personally tested more than 65 water filters, and in this guide, we’ve shared our roundup of the top-scoring and best under sink water filter systems based on contaminant reduction performance, design quality, setup and maintenance considerations, and the user experience overall.
Cloud RO
Waterdrop G3 P800
Clearly Filtered Under Sink
Table of Contents
Our Testing & Selection Process
We test all water filters ourselves to get a firsthand understanding of how they perform in real-world conditions.
Each filter receives an overall score, which is based on an average of 6 scoring factors: contaminant reduction, filtration rate, design, setup, maintenance, and company policies. Each factor is weighted based on its level of importance, with contaminant reduction being the most important and the most influential to the overall score. 
In addition, we also evaluate filter technologies and materials, as well as analyzing features that may be found in specific filter types, like efficiency ratio in reverse osmosis systems. While these are relevant to discuss, they’re not scoring factors, either because they don’t directly affect performance or because they’re not universally found across all water filters.
For our Best Under Sink Water Filter guide, we’re recommending the filters that obtained the highest overall scores.
We use numerical data where possible when analyzing and scoring water filters. But where this data isn’t available (for instance, for product quality and ease of setup & maintenance), we conduct our own subjective testing.
You can read about our testing and scoring process in more detail here.
The shortlisted best under-sink water filters are the highest-scoring filters in this product category. That means they performed better than other filters overall, receiving higher scores in categories including contaminant reduction, design, and ease of setup and maintenance.
The systems we’ve recommended each have their own unique filter technologies and are intended for different purposes. There are both reverse osmosis and non-RO systems in this list, allowing us to show you our top picks for all budgets and water treatment goals.
Some products didn’t make it onto this guide for specific reasons:
1. As this review roundup features under-sink systems only, we haven’t shared or recommended any other point-of-use filters, like faucet filters or countertop units.
2. We’ve also steered clear of manufacturers that have persistent stock issues, are known to be untrustworthy, or don’t ship their filters within the US.
3. Finally, the filters that simply performed more poorly than the top-scoring systems didn’t make the cut.
The Best Under-Sink Water Filters of 2025
| System | Cloud RO | Waterdrop G3P800 | Clearly Filtered | Waterdrop X Series | NU Aqua |
|---|---|---|---|---|---|
| Score | 9.25 | 9.21 | 9.18 | 8.42 | 8.32 |
| Type | Conventional RO | Tankless RO | Direct Connect | Tankless RO | Tankless RO |
| Price | $749 | $539 – $999 | $550 | $1,200 | $469.95 |
| Certifications or Testing | NSF 42, 53, 58 | NSF/ANSI 58, 372 | NSF 42, 372 | NSF 58 | Not Certified |
| Filter Capacity | 500 / 1,500 gal. | 550/ 1100/ 2900 gal. | 2,000 Gallons | 1,100/ 550/ 2,200 gal. | 550 / 1,100 / 3,200 gal. |
| Cost per Gallon | $0.26 | $0.11 | $0.22 | $0.14 | $0.15 |
| Warranty | 1 year | 1 year | 2 years | 1 year | 3 years |
| Read review | Cloud RO Review | Waterdrop G3P800 Review | Clearly Filtered Under Sink Review | Waterdrop X Series Review | NU Aqua Review |
Cloud RO
Cloud RO is the highest-scoring and top-performing under-sink water filtration system we tested, achieving an overall weighted score of 9.25. In our testing, this tank-based reverse osmosis system reduced or removed all contaminants with health effects in our water, and impressed us with its modern, space-saving take on the conventional, clunky under-sink RO design.
Best For
Folks looking for an under-sink reverse osmosis filter that’ll purify their tap water on demand, without the water waste and pH reduction associated with conventional systems.
Product Specs
| Price | $749 |
| Contaminants Reduced | 200+ |
| Certifications | NSF 58 |
| Process | Carbon + Reverse Osmosis + Remineralization |
| Filter Capacity | Pre/Post Filters 500 gallons, RO membrane 1,500 gallons |
| Annual Cost | ~$200 |
| Warranty | 1 year |
🎬 Video Review
Why It’s Best: Our Contaminant Reduction Testing
We tested Cloud with municipal water in Denver, Colorado. We sent two samples to Tap Score for testing: one baseline sample of unfiltered tap water, and one of water purified and dispensed from Cloud RO.
A number of contaminants with possible health effects were detected in our unfiltered water, including fluoride and two types of disinfection byproducts (both detected above the HGL), as well as copper and aluminum.
Cloud performed exactly as expected for an RO system, eliminating fluoride and both disinfection byproducts. It also removed 100% aluminum, copper, manganese, molybdenum, and strontium, and reduced sulfate by 94% and barium by 78%.
The system has an NSF certification for TDS reduction, which is a bit of a cop-out certification compared to specific contaminants we’re concerned about, but still helped bring its contaminant reduction score up to 9.42.
In all, it removed contaminants more thoroughly than any other under-sink system we tested, and the included remineralization filter prevented the negative aesthetic effects of RO purification, increasing the pH of our water from 8.4 to 9.7 (very alkaline).
Our Other Tests
We installed and used Cloud RO in our own home to see how it performed under the typical customer use conditions.
Cloud consists of two units: the main unit (containing four filter cartridges and the battery pack), and a 2.8-gallon purified water holding tank. Most components are made from BPA-free food-grade plastic, and the unit has a materials safety certification as part of its NSF 58 performance certification. We were impressed by its design, awarding a top score of 10.00 in this category.
The system works by purifying water and storing it in the tank, then using pressure to deliver it on demand to the dedicated faucet. It has a decent flow of 80 GPD (gallons per day), earning it a filtration rate score of 8.50.
As a reverse osmosis system, Cloud does waste water, but its pure-to-wastewater ratio of 1:1 means it’s far more efficient than conventional systems, which typically waste up to 4 gallons of water for every 1 gallon purified.
As for setup, the unit was easy to install, but it still received a slightly lower score of 7.50 due to the extra installation requirements for an RO system (including installing the dedicated faucet and drain line).
It redeemed itself on the maintenance front, with its score of 10.00 reflecting its affordable ongoing spend of $0.26/ gallon and its easy filter changes, with built-in sensors and a dedicated app that tracks water filter lifespan.
| Criteria | Results |
|---|---|
| Overall Score | 9.42 |
| Health Related Contaminants | 99 |
| Aesthetic Related Contaminants | 35 |
| Performance Certification | Certified for 16% of reduction claims |
| Filtration Rate | 80 GPD |
| Component Quality | Exceptional |
| Component Certification | Certified |
| Setup | Below Average |
| Servicing Requirements | Exceptional |
| Costs | $0.26/ gallon |
| Warranty Length | 1 year |
| Shipping | Free on all orders in the US |
| Returns | 12 month guarantee |
Waterdrop G3P800
The Waterdrop G3 P800 comes in close second place behind Cloud, with an overall weighted score of 9.21. It’s another reverse osmosis system, but with a tankless design (meaning purified water bypasses a tank and is sent straight to the faucet). It performed very similarly to Cloud and is certified to remove more contaminants, but the setup process was slightly trickier and its shipping and returns policies aren’t as impressive.
Best For
Anyone looking for the best under-sink RO filtration system that’s more compact than a tank-based model but still offers the same comprehensive purification.
Product Specs
| Price | $539 – $999 |
| Contaminants Removed | 1,000+ |
| Certifications | NSF/ANSI 58, 372 |
| Process | RO |
| Filtration Capacity | 550/ 1100/ 2900 gallons |
| Annual Cost | ~$145 |
| Warranty | 1 year |
🎬 Video Review
Tap Score Lab Tests
We tested the Waterdrop G3 P800 with city water in Parker, Colorado. Before filtration, 9 contaminants with health effects were detected, including lead and arsenic, both detected at concentrations above the Tap Score HGL. The G3 P800 completely removed 6 of these (including lead and arsenic) and greatly reduced barium, nitrate, and strontium.
The system is also IAPMO certified to NSF 42, for removing chlorine, and NSF 58 and NSF 53, for reducing TDS, PFOA/PFOS, fluoride, cadmium, hexavalent chromium, and selenium, barium and radium. But the model we tested didn’t include a remineralization filter*, which meant calcium and magnesium were almost completely removed, and the pH of our water dropped from 7.3 to 6.3.
Waterdrop sells a version of the G3 alongside a remineralization filter (not built in—it must be installed separately). We’ll aim to test this in the future, and we imagine this additional treatment stage will prevent the score from being affected by poor aesthetic outcomes.
Hands-on Testing
Waterdrop is similar to Cloud when it comes to smart design features, receiving a 9.70 design score. It’s made from polypropylene and polypropylene, with a space-saving design featuring built-in TDS meters, a smart faucet, and a UV purifier (to protect against bacteria growth within the filters).
Like Cloud, the G3 has a materials safety certification as a component of its NSF performance certifications. Plus, it has an IAPMO certification to NSF Standard 372 for lead-free design.
We were able to install the system ourselves, and the installation process was similar to installing Cloud, but without the water-holding tank. The G3 received a 7.00 score for setup, being more time-consuming and requiring more effort to install than the non-RO systems we tested.
Maintenance was much easier, with the built-in filter change reminder and low ongoing spend of $0.11/ gallon contributing to the unit’s 10.00 score in this category.
A big advantage of the G3 P800 is that it uses an internal pump to push water straight through the system to your faucet, giving it a fast water production rate of 800 gallons per day (10x the speed of Cloud’s filtration!) and a high score of 10.00. It’s also more efficient than Cloud, with a 3:1 pure-to-wastewater ratio.
The only setback is that, like all tankless RO systems, the G3 is susceptible to TDS creep, which may impact its efficiency and water output.
| Criteria | Results |
|---|---|
| Health Related Contaminants | 9.50 |
| Aesthetic Related Contaminants | 3.50 |
| Performance Certification | Certified for 100% of reduction claims |
| Filtration Rate | 600 or 800 GPD |
| Component Quality | Outstanding |
| Component Certification | Certified |
| Setup | Weak |
| Servicing Requirements | Exceptional |
| Costs | $0.11/ gallon (w/o remineralization), $0.13/ gallon (w/ remineralization) |
| Company | Good |
Clearly Filtered Under Sink System
The Clearly Filtered Under Sink system was the highest-scoring non-RO under-sink filter we’ve tested so far, with a few advantages versus the reverse osmosis systems: it costs less, is quicker and easier to install, and doesn’t waste water or reduce pH and alkalinity. We were impressed with how it performed in our lab tests, but it doesn’t quite match up to RO performance, and it’s only certified to reduce 1 contaminant.
Best For
Anyone looking for a non-RO under-sink system with a comprehensive contaminant reduction performance, easy setup, affordable maintenance, and no water waste.
Product Specs
| Price | $550 |
| Contaminants Reduced | 232+ |
| Certifications | NSF 42, 372 |
| Process | Carbon + Ion Exchange |
| Filter Capacity | 2,000 gallons |
| Annual Cost | ~$440 |
| Warranty | Lifetime |
🎬 Video Review
What it Removed
We tested the Clearly Filtered 3-Stage Under the Sink System on a shared, treated well water supply containing traces of contaminants including uranium, fluoride, copper, and chloroform (a disinfection byproduct), detected at concentrations exceeding the Tap Score HGL.
The unit eliminated uranium, fluoride, and chloroform, and reduced copper by 99.39%. It also removed 100% of barium and strontium (two contaminants detected below the HGL), but it only reduced 23% nitrate, 5.6% molybdenum, and 21.25% sulfate.
Unexpectedly, sodium increased by 107% and potassium by over 1,000%, while calcium decreased by 92% and magnesium by 6%, pointing to the use of a sodium- and potassium-loaded ion exchange resin. In spite of this, the pH of our water increased from 7.3 to 9.3 (alkaline).
These testing results, paired with the filter’s WQA performance certification to NSF/ANSI Standard 42 for chlorine reduction, resulted in a contaminant reduction score of 8.98.
Design, Flow Rate, Setup, & Maintenance
If you’re looking for an under-sink filter with a more DIY-friendly install process, this Clearly Filtered model should appeal. We awarded it a setup score of 9.50 as we found it significantly quicker and easier to install than the RO systems, with only a few parts and no drain line or dedicated faucet. The process took us just 15 minutes from unboxing to completion.
We measure flow rate for non-RO under-sink systems in gallons per minute, and the Clearly Filtered model had a recorded flow rate of 1.01 GPM. That’s around half the flow that you’d usually get from your kitchen faucet and is pretty decent for a filter in this category, resulting in a score of 9.00.
While the system doesn’t offer the same high-tech features as an under-sink RO unit, it still has a solid, well-thought-out design, with its sturdy construction and multiple design certifications (for materials safety and lead-free design) contributing to a design score of 9.70.
All three filters have the same projected lifespan, which simplifies maintenance, although you’ll have to make your own calendar notes to change the filters, as there’s no built-in reminder. Ongoing servicing is affordable at around $0.22/ gallon (slightly cheaper than Cloud but not as affordable as Waterdrop), translating to an overall maintenance score of 9.75.
| Criteria | Results |
|---|---|
| Overall Score | 8.79 |
| Health Related Contaminants | 95 |
| Aesthetic Related Contaminants | 99 |
| Performance Certification | Certified for <1% of reduction claims |
| Filtration Rate | 1.08 GPM |
| Component Quality | Outstanding |
| Component Certification | Certified |
| Setup | Outstanding |
| Servicing Requirements | Outstanding |
| Costs | $0.22/ gallon |
| Warranty Length | 2 years |
| Shipping | Free shipping, all orders to all states |
| Returns | 30 days |
Waterdrop X Series
Coming in behind Clearly Filtered, with an overall score of 8.42, is another tankless under-sink RO system: the Waterdrop X Series (specifically the X12). It’s IAPMO performance certified and boasts a super fast 1,200 GPD filtration rate, offering built-in remineralization (giving it an edge over the G3). But fluoride, sulfate, & strontium weren’t reduced by as much as we’d hoped, and it also introduced an unwanted contaminant into our water, hence why it didn’t land higher in this list.
Best For
Folks who want a tankless under-sink RO system that comes with a built-in remineralization filter and have the budget for a more expensive model.
Product Specs
| Price | $1,200 |
| Contaminants Reduced | 1,000+ |
| Certifications | NSF/ANSI 58 |
| Process | Mechanical + Carbon + Reverse Osmosis + UV + Remineralization |
| Filter Capacity | 1,100/ 550/ 2,200 gallons |
| Annual Cost | ~$173 |
| Warranty | Lifetime |
🎬 Video Review
Our Water Quality Tests
We tested the X12 with municipal water in Westminster, Colorado. Our tests revealed that the unfiltered tap water contained 14 contaminants with health effects, including three types of disinfection byproducts, lead, and uranium (all present in concentrations exceeding the HGLs), as well as fluoride, uranium, and other heavy metals.
The Waterdrop X12 eliminated all the contaminants that exceeded the HGL, as well as 100% of cobalt, copper, molybdenum, and zinc. It also reduced 80% fluoride, 97.93% barium, 84.44% strontium, and 92.46% sulfate.
Our test reports did show that magnesium and calcium were nearly completely eliminated, but the pH of our water only decreased slightly (from 8.5 to 8.0). This suggests that the remineralization filter was doing its job in preventing a significant pH drop.
But there was an unexpected result, too: 0.00299 PPM of antimony, a metal that has been linked to several health effects, was detected in our filtered water, exceeding Tap Score’s HGL of 0.001 PPM by 195%. It’s possible that antimony was introduced from the filters themselves or the internal plumbing in the system, as we’ve discussed in more detail in our full review.
Regardless of the reason, this outcome affected our water quality and pulled the contaminant reduction score down to 7.83. This was even with its IAPMO certifications to NSF 58 for TDS reduction and NSF 42 for chlorine reduction.
Our Performance Notes
The Waterdrop X12 has a simple, minimalistic design, with on-demand filtration (no tank!) and a small footprint. It’s a plastic unit with a few smart features, along with IAPMO certifications for materials safety and lead-free design, resulting in a design score of 9.70.
Just keep in mind that, as we mentioned in our G3 review, the X12 is susceptible to TDS creep due to its tankless design.
And, as with the G3, installation was a bit tricky due to the additional plumbing jobs needed for an RO system. The X12 received a slightly lower score of 7.00 here, based on its long 2-hour installation process that requires a bit of DIY know-how.
On a positive note, the unit has an efficient 3:1 drain ratio, so only 1 gallon of water is rejected for every 3 gallons of water purified. It’s quick and easy to maintain and received a top score of 10.00, reflecting its low cost-per-gallon of $0.14 and helpful filter change indicators on the smart faucet.
It also has a super-fast filtration rate of 1,200 GPD. This is actually excessive for most residential cases, given that most people use around 70 gallons of water a day for everything. Even so, its higher production rate earned it the highest score of 10.00 in this testing category.
| Criteria | Results |
|---|---|
| Overall Score | 8.42 |
| Health Related Contaminants | 77 |
| Aesthetic Related Contaminants | 99 |
| Performance Certification | Certified for 7% of reduction claims |
| Filtration Rate | 1,200 GPD |
| Component Quality | Outstanding |
| Component Certification | Certified |
| Setup | Weak |
| Servicing Requirements | Exceptional |
| Costs | $0.14/ gallon |
| Warranty Length | 2 years |
| Shipping | Free shipping to lower 48 US states |
| Returns | 30 days |
NU Aqua
Rounding off this list of the top-performing under-sink water filters is the NU Aqua Efficiency Series, another tankless RO system. This unit earned an overall weighted score of 8.32, with its overall-pretty-good contaminant reduction performance and decent 2:1 efficiency ratio let down slightly by its lack of certifications, unusual testing outcomes, and inability to reduce fluoride in our testing.
Best For
People looking for a more affordable alternative to the Waterdrop G3 P800 that offers the same flow rate and a similar efficiency and overall performance
Product Specs
| Price | $469.95 |
| Contaminants Reduced | 10+ |
| Certifications | Not Certified |
| Process | GAC + RO + UV |
| Filter Capacity | 550 / 1,100 / 3,200 gal. |
| Annual Cost | ~$200 |
| Warranty | 3 years |
Lab Performance Data
We tested the NU Aqua Efficiency Series in a home on treated well water, which contained 3 contaminants exceeding the HGL: arsenic, uranium, and (most concerningly) lead. Copper, molybdenum, nitrate, phosphorus, iron, selenium, boron, and fluoride were also detected, but at concentrations below the HGL.
The Efficiency Series reduced most contaminants by at least 70%, including complete eliminations of copper, lead, molybdenum, phosphorus, and uranium. The only letdown was fluoride, which remained the same (0.004 PPM) post-filtration, possibly removed and reintroduced by the remineralization media.
Concerningly, a number of contaminants were detected post-filtration when they weren’t present in our baseline sample. These included:
- Antimony
- Barium
- Boron
- Cobalt
- Coliform bacteria
- Iron
- Manganese
- Nickel
- Selenium
- Strontium
- Thallium
- Toluene
We suspect that the bacteria came from the homeowner accidentally contaminating the RO faucet when they put it in their water bottle to fill it, and was then imparted to the sample vial. The toluene may have been leaching from the plumbing or (more concerningly) the RO system itself. Everything else most likely came from the remineralization filter and was detected at concentrations not quantifiable by the testing lab and/or below the HGL.
Speaking of remineralization, we saw some significant increases in minerals like calcium, magnesium, and potassium, and an increase in pH from 7.6 to 7.8.
Ultimately, though, the presence of new contaminants and the filter’s inability to remove fluoride, along with its lack of performance certifications, resulted in the lowest contaminant score so far: 7.89.
Hands-on Tests
The Efficiency Series has a tankless design, with three filters stored inside the main unit, a separate post-remineralization filter and UV sterilizer, and a dedicated faucet to install at the sink. While it seemed sturdy enough, its lack of a materials safety certification pulled its design score down to 8.9.
Setup was similar to the Waterdrop G3 and Cloud systems, with the tedious tasks of installing the faucet and drainline leading to a lower score of 7.00. But once installed, the unit’s filtration rate of 800 GPD meant we had instant access to purified water, putting it neck-and-neck with Waterdrop and earning it a top score of 10.00.
Where this system does fall short is performance efficiency. It only wastes 1 gallon of water per every 2 gallons purified, which still makes it highly efficient, but slightly more wasteful than Cloud and Waterdrop.
But maintenance was as easy as for all the other under-sink RO systems in this list, with the system’s affordable cost-per-gallon of $0.15 and filter change lights earning it a score of 10.00.
| Criteria | Results |
|---|---|
| Overall Score | 8.32 |
| Health Related Contaminants | 8.00 |
| Aesthetic Related Contaminants | 9.90 |
| Performance Certification | Not Certified |
| Filtration Rate | 600 or 800 GPD |
| Component Quality | Outstanding |
| Component Certification | Not Certified |
| Setup | Weak |
| Servicing Requirements | Exceptional |
| Costs | $0.15/ gallon |
| Warranty Length | 3 years |
| Shipping | Free shipping on orders over $40 within the contiguous 48 US states |
| Returns | 120 days guarantee, with stipulations |
Hi, just curious why Aquatru didn’t make the list. Do you have a review for the aquatru under sink RO filter? I only see the countertop version on your site. Thanks!
I havnt tested the under sink Aquatru system yet, though it is on my to-do list. That said, it uses the exact same extensively certified filter elements as the Classic countertop unit, so I’d expect very similar performance in our scoring system to that one.
Would you advise using the Epic Smart Shield Max? It uses the same carbon block as the normal Smart Shield, but also has an exterior layer of nano fabric to filter VOCs, microplastics, etc. Curious if you’d recommend something like this or think the original Smart Shield is better.
I have not tested the new Epic Smart Shield Max yet, though it is on my to-do list. I recommend matching the filter to the contaminants of concern in your water, ideally using a filter certified to reduce what you need to
any NANOfilters that dont have a single plastic component? (including the filters)
No
Hi, I was wondering if the Epic Smart Shield can be used under a bathroom vanity sink. If so, can the sediment attachment be used along with It?
Thank you!
Yes, as long as there is room under the bathroom sink and the plumbing connection is the right size