5 Best Under Sink Water Filter Systems We’ve Tested

Our Testing & Selection Process

How we tested these under-sink filters: We installed and lived with each system, then sent before-and-after water samples to an accredited third-party laboratory to measure exactly what each filter removed, and just as importantly, whether it added anything. Each system earns a weighted overall score out of 10 across six factors: contaminant reduction (weighted most heavily), filtration rate, design, setup, maintenance, and company policies. Because we test the filtered output and not just the manufacturer’s claims, our scoring captures real-world results that manufacturer testing may miss, including two systems in this guide that introduced new contaminants we did not start with. We have personally tested more than 70 water filters to date. Brian Campbell, who leads our testing, is a WQA Certified Water Specialist with 10+ years in water treatment.

Article Update History

• 06/27/2026 – Removed Waterdrop X12 and Nu Aqua Efficiency series. Added Frizzlife PD600 TAM3 and APEC ROES-PH75
• 06/05/2026 – Cloud RO scores recalculated for accuracy

The Best Under-Sink Water Filters of 2026

System	Cloud RO	Waterdrop G3P800	Clearly Filtered	Frizzlife PD600-TAM3	Apec Roes-Ph75
Score	9.24	9.21	9.18	8.94	8.87
Type	Conventional RO	Tankless RO	Direct Connect	Under-sink RO	Under-sink RO
Price	$649	$539 – $999	$550	$376	$268.99
Certifications or Testing	NSF 42, 53, 58	NSF/ANSI 58, 372	NSF 42, 372	NSF 372	NSF 58
Filter Capacity	500 / 1,500 gal.	550/ 1100/ 2900 gal.	2,000 Gallons	900 – 1,800 gallons	6-24 months
Cost per Gallon	$0.26	$0.11	$0.22	$0.10	$0.10
Warranty	1 year	1 year	2 years	1 year	1 year (Limited)
Read review	Cloud RO Review	Waterdrop G3P800 Review	Clearly Filtered Under Sink Review	Frizzlife PD600-TAM3 Review	APEC ROES-PH75 Review

Cloud RO: Best Overall Under-Sink Filter (9.24/10)

Cloud RO is the highest-scoring and top-performing under-sink water filtration system we tested, achieving an overall weighted score of 9.24. 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.  

Overall Score: 9.24

How We Test & Score

9.42 Contaminant Reduction

10.00 Design

10.00 Maintenance

8.50 Filtration Rate

7.50 Setup

9.20 Company

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	$649
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

View at cloudwaterfilters.com

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🎬 Video Review

We tested Cloud twice with two different municipal water supplies in Colorado. For each test, 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. 

In test 1, 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%.

In test 2, our baseline sample had a TDS reading of 707 PPM — that’s almost 10x the dissolved solids concentration of our test 1 water source.

Barium, nitrate, nitrite, three disinfection byproducts, total chromium, copper, molybdenum, fluoride, manganese, boron, and uranium were among the contaminants with health effects detected, and all three DBPs were detected above the HGL.

This time, Cloud eliminated fluoride, all three disinfection byproducts, uranium, copper, strontium, selenium, manganese, potassium, molybdenum, and nitrate. It also greatly reduced barium by 97%, sulfate by 95%, and total chromium by 93%.

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).

How easy is Cloud RO to install and maintain?

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), and in our tests, at a feed water temperature of 57.5°F and a static water pressure of 50 PSI, it had a filtration rate of approximately 65.17 GPD. This earned it a 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. This was corroborated by our own tests, which recorded a pure-to-wastewater ratio of approximately 1:1.3 when purifying 12 ounces, and 1:1.03 when purifying 64 ounces.

We also tested the installed system for TDS creep, and Cloud had a 1st draw TDS reading of 284 PPM. At first glance, this is indicative of TDS creep, especially when we compared it to our second draw sample reading, which we took after running water through the system for 2 minutes: 68 PPM.

But our contact at Cloud explained that this was actually caused by minerals leaching from the new remineralization media and should normalize after a few weeks.

As for setup, the unit was easy to install, and all the fittings and filters are pre-installed, 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.

Waterdrop G3 P800: Best Tankless RO Under-Sink System (9.21/10)

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.

Overall Score: 9.21

How We Test & Score

9.28 Contaminant Reduction

9.70 Design

10.00 Maintenance

10.00 Filtration Rate

7.00 Setup

8.65 Company

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

View at waterdropfilter.com

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🎬 Video Review

What did the Waterdrop G3 P800 remove in lab testing?

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.

When we tested it without the optional remineralization filter, the G3 P800 completely removed 6 of these (including lead and arsenic) and greatly reduced barium, nitrate, and strontium.

With remineralization, our results were even better: the G3 eliminated all contaminants detected above the HGL, including fluoride. It completely removed barium, copper, selenium, molybdenum, and vanadium. Additionally, strontium was reduced by 97%, and total chromium by 88%.

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. Without the remineralization filter, calcium and magnesium were almost completely removed, and the pH of our water dropped from 7.3 to 6.3. With remineralization, pH was only reduced from 8.0 to 7.5.

Is the Waterdrop G3 P800 certified for materials safety?

Waterdrop is similar to Cloud when it comes to smart design features, receiving a 9.70 design score. It’s made from polypropylene and ABS, 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. In our own testing, at a feed water temperature of 58.3°F, we measured the G3’s flow rate as approximately 886.54 GPD.

It’s also more efficient than Cloud, with a 3:1 pure-to-wastewater ratio.  When we tested efficiency ourselves, the unit had a recovery rate of 1:0.6 when purifying 12 ounces of water, and 1:0.45 when purifying 64 ounces of water.

Tankless RO systems are susceptible to TDS creep, which may impact their efficiency and water output. But in our on-site tests, the unit’s first-draw reading was higher than the second-draw reading by just 33 PPM, which is not indicative of TDS creep.

Clearly Filtered: Best Non-RO Under-Sink Filter (9.18/10)

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. 

Overall Score: 9.18

How We Test & Score

8.98 Contaminant Reduction

9.70 Design

9.75 Maintenance

9.00 Filtration Rate

9.50 Setup

9.00 Company

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	2 years

View at clearlyfiltered.com

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🎬 Video Review

What did the Clearly Filtered under-sink system remove?

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.

Is the Clearly Filtered under sink filter easy to install?

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 1.08 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.

Frizzlife PD600-TAM3: Best Budget Tankless RO (8.94/10)

The Frizzlife PD600-TAM3 is our top recommend under-sink RO system for small budgets, achieving an overall score of 8.94. With its external remineralization filter and space-saving tankless design, it offers a bit more than some of its competitors. We were generally impressed with its contaminant reduction, flow rate, and efficiency ratio, although it’s lacking official certifications for performance and materials safety, and its design quality doesn’t match up to others.

Overall Score: 8.94

How We Test & Score

9.00 Contaminant Reduction

8.80 Design

10.00 Maintenance

10.00 Filtration Rate

7.00 Setup

8.20 Company

Best For

People looking for a more affordable alternative to the Waterdrop G3 P800 that offers a similarly fast flow rate, as well as a similar overall performance.

Product Specs

Price	$376
Contaminants Reduced	14+
Certifications	NSF 372 (lead-free materials only)
Process	Carbon pre-filter + RO membrane + Alkaline remineralization filter
Filter Capacity	900 – 1,800 gallons
Annual Cost	~$130
Warranty	1 year

View at frizzlife.com

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🎬 Video Review

What contaminants did the Frizzlife PD600-TAM3 remove in our lab testing?

When we tested the PD600-TAM3, 16 contaminants with possible health effects were detected in our baseline water sample, including:

• 3 disinfection byproducts
• Uranium
• Fluoride
• Several heavy metals, including copper and barium
• Nitrate
• Several metals and metaloids, including strontium and boron
• Chromium

5 of these contaminants were detected at levels exceeding the HGL: all 3 disinfection byproducts (dibromochloromethane, bromodichloromethane, and bromoform), as well as uranium and fluoride. 

Post-filtration, our water quality was significantly better. Barium, total chromium, copper, the 3 disinfection byproducts, fluoride, manganese, molybdenum, selenium, strontium, uranium, sulfate, and vanadium were all reduced by at least 90%.

But there was still room for improvement: only 38.8% of boron was reduced, along with just 50% of nitrate.

As for pH and minerals, our feedwater had a pH of 7.4, making it slightly alkaline. The pH of our purified water was higher: 8.13. Calcium was still reduced by 86%, magnesium and sodium by 95%, and potassium by 100%. 

So far, our results are similar to the Waterdrop G3’s — but the PD600-TAM3 had an issue with TDS creep, while the G3 did not. The PD600-TAM3 had a 1st draw TDS reading of 474 PPM, which is indicative of TDS creep, since the feed water TDS was 645 PPM. This was reduced to 40 PPM once we ran water through the system for 2 minutes.

How easy is the Frizzzlife filter to install?

The PD600-TAM3 is a space-saving under-sink unit that consists of one main tank (containing two filter cartridges) and a separate external remineralization filter.

It seems pretty sturdy, but we noted that the ¼” quick-connect components feel cheaper and flimsier than in similar RO systems we tested. However, the system does have an IAPMO certification to NSF 372, for lead-free design, resulting in a score of 10.00 and bringing its overall component quality score up to 8.00. 

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. The installation took 90 minutes in total; 3x the time suggested by Frizzlife, extended by certain issues (the 1/4 tubing isn’t pre-cut or color-coded, and the gasket in the 3-way feed water valve falls out easily).

But once installed, the unit’s listed filtration rate of 600 GPD meant we had instant access to purified water. In our own flow rate testing, at a feed water temperature of 60.9°F, it had a flow rate of just over 639 GPD — not quite as fast as the G3, but still earning it a top score of 10.00.

Where this system does fall short is performance efficiency. It has a listed efficiency ratio of 2:1, meaning 1 gallon of water is lost for every 2 gallons purified. In our on-site tests, it had a pure-to-drain ratio of 1:1 when filtering 12 ounces of water, and 1.52:1 when purifying 64 ounces. That’s not bad, but it doesn’t compare to high-efficiency systems like 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 $0.10 and filter change lights earning it a score of 10.00. 

APEC ROES-PH75: Best Budget Conventional RO (8.87/10)

Coming in behind Frizzlife, with an overall score of 8.87, is our top recommended budget-friendly conventional under-sink RO system: the APEC ROES-PH75. It’s WQA performance certified and holds two design certifications, offering built-in remineralization for convenience. But the installation process is time-consuming and tricky, and filtration and efficiency ratio are pretty poor when we compare the unit to other RO systems

Overall Score: 8.87

How We Test & Score

9.28 Contaminant Reduction

9.70 Design

9.25 Maintenance

7.50 Filtration Rate

7.00 Setup

8.35 Company

Best For

Folks who want an affordable conventional under-sink RO system that comes with a built-in remineralization filter and NSF certifications.

Product Specs

Price	$268.99
Contaminants Reduced	10+
Certifications	NSF/ANSI 58
Process	Sediment + Carbon + RO + Remineralization
Filter Capacity	6-24 months
Annual Cost	~$133
Warranty	1 year (Limited)

View on apecwater.com

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▶️ Video Review

How did the ROES-PH75 perform in our lab tests?

We tested the APEC ROES-PH75 with municipal water in Colorado. Our tests revealed that the unfiltered tap water contained 16 contaminants with health effects, including three types of disinfection byproducts, fluoride, and uranium (all present in concentrations exceeding the HGLs), as well as copper, nitrate, and other heavy metals.

The unit eliminated all the contaminants that exceeded the HGL, as well as 100% of molybdenum, selenium, sulfate, chlorine, and vanadium. The system also greatly reduced barium by 98%, strontium by 96%, chromium by 86%, nitrate by 64%, and boron by 49%.

Manganese increased by 40% post-filtration, from 0.0011 PPM to 0.00155 PPM. We think this trace increase is likely coming from the remineralization filter. 

Our test reports did show that magnesium and calcium were nearly completely eliminated, but the pH of our water increased from 7.59 to 8.77 in our on-site pH meter tests. This suggests that the remineralization filter was doing its job in preventing a significant pH drop.

The system showed no evidence of TDS creep in our comparison tests, and its performance certification by the WQA to reduce TDS earned it an overall contaminant reduction score of 9.28.

How hard is the APEC ROES-PH75 to install?

The APEC ROES-PH75 2 has a simple, tank-based design, with three filters mounted vertically below, and two stacked horizontally on top. 

It’s a plastic unit with a 4-gallon storage tank for purified water, along with materials safety certification as a component of its NSF 58 performance certification and a WQA certification for lead-free design, resulting in a design score of 9.70.

As with the other systems in this list, installation was a bit tricky due to the additional plumbing jobs needed for an RO system. The ROES-PH75 received a slightly lower score of 7.00 here, with a couple of unhelpful features making installation unnecessarily more time-consuming: the filters and housings aren’t color-coded, and the faucet doesn’t have a quick-mount nut.

Once installed, the unit is quick and easy to maintain and received a score of 9.25, reflecting its low cost-per-gallon of $0.12 but pulled down by its lack of integrated filter life tracker or filter change reminder.

APEC lists a 1:3 pure-to-drain ratio, but in our tests, it had a recovery rate of just 1:10.6. That means 10.6 ounces of water is wasted per 1 ounce purified, making the ROES-PH75 the least efficient RO system we’ve tested by a mile.

It also has a slower filtration rate of 42.74 GPD, slightly below APEC’s listed maximum flow rate of 75 GPD. As a result, it received a score of of 7.50 in this testing category

Frequently Asked Questions

Q: What is the best under-sink water filter?

A: Based on our hands-on testing and accredited lab analysis, the best under-sink water filter is the Cloud RO (9.24/10). It removed or reduced every health-related contaminant in our test water, earned the highest contaminant reduction score of any under-sink system we have tested, and delivers purified water on demand from its tank with a 1:1 efficiency ratio.

Q: Are under-sink reverse osmosis systems better than non-RO filters?

A: For thoroughness, yes. The RO systems we tested removed more contaminants more completely than non-RO filters. The tradeoff is that RO wastes some water, can lower pH unless remineralization is included, and takes longer to install. The best non-RO option we tested, the Clearly Filtered Under Sink (9.18), still eliminated uranium, fluoride, and chloroform while installing in about 15 minutes with no water waste, so it is a strong choice if you want simplicity over maximum contaminant reduction.

Q: Can an under-sink water filter add contaminants to your water?

A: It can, which is why we lab test the filtered output rather than trusting marketing claims. In this guide, the APEC ROES-PH75 showed a 40% increase in manganese after filtration, a trace amount we attribute to its remineralization media. Catching changes like this is only possible by testing the filtered water, since they never appear on a manufacturer’s claim sheet.

Q: Does an under-sink filter need to be NSF certified?

A: Certification is reassuring but not legally required. We distinguish between a system genuinely certified for the contaminants you care about and one with a narrow or materials-only certification. For example, the Waterdrop G3 P800 and APEC ROES-PH75 are certified for the bulk of their reduction claims, while the Clearly Filtered system is certified for under 1% of its claims and the Frizzlife PD600-TAM3 carries only a lead-free materials certification, not a performance certification. We recommend matching the filter to the contaminants in your water, ideally confirmed with a certified lab water test.

Q: How much does it cost to run an under-sink water filter?

A: Ongoing cost is primarily driven by filter replacements, which we standardize and express as cost per gallon. Among the systems we tested, this ranged from about $0.10 per gallon (Frizzlife PD600-TAM3) to $0.26 per gallon (Cloud RO). Annual filter costs in this guide run roughly $130 to $440 depending on the system and your water usage.

Q: How hard is it to install an under-sink water filter yourself?

A: It depends on the type. The non-RO Clearly Filtered system installed in about 15 minutes with no drain line or dedicated faucet, earning a 9.50 setup score. The RO systems took longer, around 90 minutes for the Frizzlife PD600-TAM3, because they require installing a dedicated faucet and drain line, which is why RO units scored lower (7.00 to 7.50) for setup in our testing.