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Best Under-Sink Water Filter Systems of 2023

Scott Winfield
Written by Scott Winfield
Last Updated on

If you’re in the market for an under-sink water filter, you can’t just go and test each and every product by yourself, right? Well, we have good news because we’ve done that for you!

For almost a year now, we’ve been installing and uninstalling different filtration systems. As a result, we’ve been able to test the quality, reliability, and cost/efficiency of many products on the market and have come up with a guide that lists the best systems available.

In the end, our #1 choice is the super-strong favorite for an overall under-the-sink filtration system. For those looking for a portable system, we definitely recommend our #3. And, if you have space problems under your sink, but don’t want to sacrifice water capacity, #4 is there for you.

Water Filtration System for Sink Reviews

Clearly Filtered 3-Stage Under the Sink Water Filter System

3-Stage Under the Sink Water Filter System
  • Type: 3-stage filtration
  • Contaminants Removed: 232+ contaminants, including sediments, heavy metals, VOCs, sodium fluoride, asbestos, radiation, and lead.
  • NSF Certification: NSF Standards 42, 53, & 401
  • Filter Capacity: 2,000-gallon for each filter
  • Warranty: 30-day worry-free trial, limited lifetime warranty
  • Removes more than 232 contaminants with great success
  • Very easy to install for DIYers
  • Low maintenance
  • Has three different NSF certifications
  • Doesn’t remove beneficial minerals from the water
  • Minimum wastewater
  • Might decrease the water pressure

The under-the-sink filter system by Clearly Filtered is clearly our favorite since it can remove more than 232 different contaminants. In that sense, it’s the most powerful under sink filter on the planet that’s been independently tested. Moreover, considering its unprecedented contaminant removal success rate, it comes at a reasonable price.

The removal success of the Clearly Filtered is indebted to its innovative filters that subject the tap water to three stages of purification: an advanced priming filter, a second filter that specifically targets heavy metals and VOCs (volatile organic compounds), and a built-in fluoride filter.

The advanced priming filter, which is actually Clearly Filtered’s sophisticated take on coconut carbon pre-filters, reduces the number of sediments in the water. This process prepares the water for further stages of filtration while also getting rid of its nasty odor, bad taste, and color.

In the second stage, another advanced filter is employed to minimize the chemical hazards present in both municipal water systems and well water with great success. It reduces herbicides, pesticides, radiation, and heavy metals such as arsenic (by 94.3%), lead (by 98.9%), and manganese (by 99.9%) as independently tested in accordance with NSF standards.

However, what really stood out for us is the built-in fluoride filter of the third stage, which is actually a great alternative to traditional RO (reverse osmosis) filters. Unlike RO filters, it doesn’t eliminate beneficial minerals or waste a lot of water during the filtration process. Moreover, its fluoride removal ratio of 90.7% is superior to what most RO filters on the market are capable of (80% to 90%).

Afraid that such great filtration means an arduous installation process? Don’t be! Anyone can DIY-install the Clearly Filtered in under fifteen minutes only with the help of a wrench.

Additionally, it’s compatible with any kind of sink and faucet, doesn’t require power to work, and all of its filters are twist-off and need to be replaced only once a year. So, both its installation and maintenance are quite easy, which is another reason why it’s our favorite.

Lastly, we should also note that it might sometimes decrease the water pressure by 20%. However, such thorough filtration means that the incoming water should spend some contact time with filters, and the decrease in the water pressure can therefore be easily forgiven.

Aquasana OptimH2O

OptimH2O® Reverse Osmosis + Claryum®
  • Type: Reverse osmosis
  • Contaminants Removed: 88 contaminants, including VOCs, heavy metals, lead, arsenic, and fluoride.
  • NSF Certification: NSF Standards 42, 53, 58, & 401
  • Filter Capacity: 13.32 GPD (gallons per day)
  • Warranty: 90-day guarantee, 2-year warranty
  • Removes 88 contaminants with a 99% success rate
  • Highly affordable
  • Features a remineralizer
  • Low maintenance
  • Has four different NSF certifications
  • Requires plumbing knowledge to install
  • Extremely high wastewater ratio
  • Two-year warranty implies a short projected lifespan for the product

Sometimes, all we want in the space under our sink is a traditional filtration system that employs reverse osmosis and features a tank. The best item on the market that fits that criterion happens to be the Aquasana OptimH2O.

Although its capability to remove only 88 contaminants (see page 16 of the owner’s manual for the full list) is a bit underwhelming compared to the numbers the Clearly Filtered boasts, there should be no cause for concern. The Aquasana OptimH2O is capable of removing a majority of hazardous contaminants with 99% success rate.

How does it do that? With the help of a 4-stage filtration process. The first stage of the process is pretty standard: an activated carbon filter that removes organic chemicals, including VOCs, herbicides, and pesticides.

After that, though, we’re introduced to Aquasana’s signature designs: The OptimH2O Reverse Osmosis and Claryum. The OptimH2O Reverse Osmosis is a unique RO design that can filter any dissolved solid material smaller than one micron. Thanks to that, the levels of fluoride, arsenic, and radium that reach the faucet are significantly reduced.

Once the dissolved solids are taken care of, the water moves into the Claryum filter, which combines activated and catalytic carbon block techs in the same ion-exchange filter. This filter is capable of removing many sub-micron contaminants like heavy metals.

What’s more, Aquasana throws a remineralizer into the mix, retaining beneficial minerals usually lost through reverse osmosis. The OptimH2O adds healthy doses of potassium, magnesium, and calcium back into the water. In the end, the water isn’t only healthy but tastes great as well.

Similar to the Clearly Filtered, all the filters of the Aquasana OptimH2O are also twist-off. While the RO membrane and remineralizer can last a year, all the other filters need to be replaced once every six months.

However, the installation process is where the Aquasana differs from the Clearly Filtered. It requires lots of tools and plumbing knowledge, so it’s better to employ professional help.

Moreover, its wastewater ratio is quite the opposite of eco-friendliness: for a cup of pure drinking water, it sends four cups down the drain. The two years of warranty the company offers isn’t ideal either.

All in all, though, it’s quite budget-friendly, NSF-certified, and its contaminant removal ratio is quite splendid, giving it the #2 spot on our list.

Epic Smart Shield

Epic Smart Shield
  • Type: Single carbon block filter
  • Contaminants Removed: 70 contaminants, including heavy metals, chlorine, chloramine, lead, asbestos, microplastics, uranium, and fluoride.
  • NSF Certification: NSF Standards 42, 53, & 401
  • Filter Capacity: 651 gallons of filter life
  • Warranty: 100% lifetime warranty
  • Removes 70+ contaminants with a great success rate
  • Eco-friendly
  • Extremely affordable
  • Very easy to install
  • Doesn’t remove beneficial minerals during the filtration process
  • Compact and portable
  • Doesn’t have enough power to purify well water
  • Doesn’t feature a sediment filter
  • Replacement filters can be slightly expensive

For those looking for a portable under-sink water filtration system, there’s no better option than the Epic Smart Shield. Its single filter doesn’t weigh much, it occupies very little space, it’s incredibly easy to install and uninstall, and it’s a friend to every budget.

That doesn’t mean it’s less efficient in terms of purifying water, either. Similar to the high-end options above, it’s NSF-certified, and it can remove more than 70 contaminants from tap water with a 99% success rate.

If the quantity of removed contaminants seems a bit on the lower side, we should lay concerns to rest—it removes all the most dangerous elements. These include heavy metals, agricultural contaminants, pharmaceuticals, chlorine, and chloramines. Its fluoride removal rate of 97.88% is even better than what the Clearly Filtered and the Aquasana OptimH2O have to offer.

Moreover, unlike the Aquasana OptimH2O, it doesn’t need to employ a remineralizer. The filtration system leaves potassium, calcium, and magnesium intact, so the water doesn’t lose its essential minerals during the purification process.

The filter features a solid carbon block design, and it’s completely BPA- (bisphenol A) and lead-free. What’s more, despite its humble look when compared to other items on our list, it can produce 651 gallons of purified water over the span of one year. That number is equal to 1,500+ plastic water bottles.

Its eco-friendliness isn’t limited to preventing plastic bottles from going to landfills, either. We particularly like Epic Smart Shield because its filter is made of 100% recyclable materials.

The company is also a member of the 1% for the planet project, and they even run their own recycling program. Should you register to it and send them three used Epic Smart Shield filters to be recycled, you will receive a new filter for free!

Nonetheless, note that without registering with the recycling program, the replacement filters may cost as much as the whole system itself. Especially considering that the lifespan of the filter is only one year, it adds up to quite an expense in the long run.

Moreover, the system doesn’t feature a sediment filter, nor is it as powerful as the other filters on our list. Therefore, we don’t recommend it for purifying well water. Those who are living in municipalities where the quality of the water is too low should also stick to other alternatives on this list.

That being said, the Epic Smart Shield is still a decent buy for those looking for an especially portable, eco-friendly, and affordable product.

Waterdrop G3P800

800 GPD Tankless RO System with UV Sterilizing Light and Smart Faucet - Waterdrop G3P800
  • Type: Reverse osmosis and UV sterilizer
  • Contaminants Removed: An unspecified number of contaminants, including TDSs, PFASs, VOCs, heavy metals, lead, bacteria, chlorine, and fluoride.
  • NSF Certification: NSF Standard 58
  • Filter Capacity: 800 GPD (gallons per day)
  • Warranty: 30-day guarantee, unspecified warranty
  • Highly efficient 7-stage filtration process
  • Compact
  • Features a UV sterilizer
  • Features its own faucet with a smart LED screen
  • Easy to install
  • Expensive
  • Wastes water
  • Incompatible with well water
  • Doesn’t feature an NSF-verified list of removed contaminants

The Waterdrop G3P800 is surely a luxury to have. It looks too nice for a filtration system that’s going to be tucked in under a sink, but more importantly, it’s quite powerful in terms of removing contaminants. In addition, its water capacity of 800 GPD can easily accommodate large households, offices, schools, and even restaurants.

The filtration process of the G39800 consists of seven stages:

  1. First PP cotton layer: The first stage aims to eliminate large particles and sediments like rust, sand, and nematodes with a polypropylene (PP) cotton filter.
  2. Scale inhibitor: Water scale can ruin clothes and kitchen appliances and give fruits and veggies a nasty texture after washing. The scale inhibitor membrane of the G3P800 reduces limescale formation to a significant extent.
  3. Activated carbon block filter: In this stage, many dangerous metals like lead and chemicals like fluoride and chlorine are taken care of. As a result, the nastiness in the taste and odor of the water is also gone.
  4. Second PP cotton layer: If there are any large particles left standing after the first three stages, the second polypropylene cotton filter makes sure that they are no more.
  5. Reverse osmosis membrane: Any impurity that’s larger than 0.0001 micron is filtered out by this highly efficient RO membrane. The list includes totally dissolved solids (TDSs), perfluoroalkyl and polyfluoroalkyl substances (PFAS), and bacteria.
  6. Post-activated carbon filter: In the sixth stage, the post-filter ensures that no VOCs and chlorine make their way into the faucet.
  7. UV sterilizer: As the last line of defense, the Waterdrop G3P800 employs a UV sterilizer that has a sterilization rate of 99%.

In addition to all these great filtration features, we like the G3P800 specifically because it fits quite well under the sink. Since it doesn’t have a tank, it doesn’t lead to any bacterial formation around it either.

Moreover, like the Clearly Filtered, any DIYer without prior plumbing experience can install it quite easily. The filters and the RO membrane should be replaced once every 6-12 months, depending on the usage.

In the package, Waterdrop also includes a faucet with a smart LED screen on which the filtration process can be tracked, and any malfunction is reported. In that sense, it’s easy to maintain as well.

However, all these great features come at a high cost, as it’s the priciest product on our list. Moreover, it’s incompatible with well water, and it wastes one cup of water to produce three drinkable ones. Although it’s NSF-certified, unlike other systems we’ve reviewed so far, it doesn’t feature a list of removed contaminants either, which is slightly disappointing.

 Frizzlife PD600

Frizzlife Tankless Reverse Osmosis System With Alkaline Remineralization - PD600-TAM3
  • Type: Reverse osmosis and alkaline remineralizer
  • Contaminants Removed: An unspecified number of contaminants, including TDSs, PFASs, VOCs, mercury, lead, asbestos, chlorine, and fluoride.
  • NSF Certification: Not certified
  • Filter Capacity: 600 GPD (gallons per day)
  • Warranty: Limited one-year warranty
  • 7-stage filtration is state-of-the-art
  • Alkaline remineralizer provides healthy and tasty water
  • Looks aesthetically cool
  • Easy installation
  • Not certified by NSF
  • Not independently tested
  • Limited warranty of one year is quite short

The tankless Frizzlife PD600 is unlike any other filtration system on our list. It has a space-age look, and although it employs reverse osmosis like many of its counterparts, it aims to neutralize the negative effects of RO with its alkaline remineralizer. That’s surely a breath of fresh air in this line of industry, and that’s why we liked it so much.

Its filtration process is quite similar to that of the Waterdrop G3P800—at least up until the last stage. The first six stages, including the 0.0001-micron RO membrane, consist of many attempts to eliminate contaminants from the water.

As a result, many dangerous chemicals (like arsenic, asbestos, and fluoride), heavy metals (like lead, mercury, and radium), VOCs, and TDSs are removed. If there’s any foul taste or odor to the water, it’s taken care of as well.

After the elimination of contaminants, though, the Frizzlife PD600 differs from the Waterdrop. Instead of a UV sterilizer, it employs an alkaline remineralizer.

You see, the water that passes through RO membranes is generally acidic, and the RO process removes many beneficial minerals. Many filtration systems aim to minimize that drawback by including a remineralizer in the last stage.

However, the reason that the Frizzlife PD600 stands out and why we like it is that its remineralizer isn’t like the others. It’s an alkaline remineralizer that readjusts the alkalinity of the end-product by bringing pH to its natural level above the 7.5 threshold. In the process, it also adds beneficial minerals like potassium and calcium back into the water.

In addition, it features a smart filter life reminder that leaves no room for doubt about when to replace filters. Filter replacement is eco-friendly as well since only the cartridge inside the plastic housing should be changed, which significantly reduces plastic waste in the long run.

The installation process is also quite simple. It’s pretty well laid out in the owner’s manual, and the product page on the Frizzlife website includes a video guide on installation.

Nonetheless, the Frizzlife PD600 hasn’t been independently tested (our analysis notwithstanding), nor is it up to NSF standards. Therefore, although it boasts 1000+ removed contaminants, that claim isn’t backed up scientifically. Frizzlife also doesn’t provide a full list of removed contaminants.

Moreover, only one year of limited warranty offered by Frizzlife is quite humble against what our top three have. That said, it produces drinking water that really tastes great.

How We Reviewed Under Sink Water Filter Systems

When testing the under-sink water filters listed above, these are the criteria we adhered to:

  • How effective they were in removing contaminants,
  • Whether they were independently tested and NSF-certified,
  • What kind of filtration technology they employed,
  • How easy they were to install,
  • Whether they required high or low maintenance,
  • What warranty options the brands were offering,
  • And, of course, how much they cost.

Let’s revisit how our top five fared on each of these fronts as well as explain our benchmarks a little better.

Contaminants Removed

Unfiltered municipal tap water contains many contaminants that may present a hazard to our health either in the short or the long term. These include blatantly dangerous elements like VOCs, heavy metals, and disease-bearing bacteria, but also subtle threats like pharmaceutical or agricultural waste.

Therefore, the success of a water filtration system depends on its ability to remove as many contaminants as possible. However, certain further questions emerge when dealing with contaminant removal numbers:

  • How can we be sure that they remove these contaminants?
  • Do the numbers that brands boast reflect the truth?

Well, the best products on the market, like our top three, are tested independently in labs that apply NSF standards, and they offer a full list of removed contaminants, including the removal success rate. Among them, the Clearly Filtered especially shines due to the 232+ contaminants it can remove and its high removal success rate.

Some, on the other hand, like the last two products in our top five, fail to provide customers with such assurance but still remove many contaminants. Both Waterdrop and Frizzlife claim that their products can remove more than 1000 contaminants, but these claims lack any proof.

Water Filters (Best to Worst)Contaminants Removed
Clearly Filtered232+ (independently tested)
Aquasana OptimH2O88+ (independently tested)
Epic Smart Shield70+ (independently tested)
Waterdrop G3P8001000+ (not tested)
Frizzlife PD6001000+ (not tested)

NSF Certification

Founded in 1944 as a global and independent organization, the National Sanitation Foundation works to test, inspect, and certify whether our buildings, automobiles, food, and water are up to certain health standards.

In the industry of water filtration, tests conducted by NSF-approved labs help companies verify the effectiveness of their products, especially when it comes to removing contaminants. After the tests, some of these products get certified by the NSF.

The products we included in our top five had four different NSF certifications among them. Our #2, the Aquasana OptimH2O, has them all:

  • NSF 42:The NSF 42 certification means that a filtration system is able to remove basic taste-altering and odor-causing contaminants. It also entails chlorine as, more often than not, it’s the culprit for bad taste and odor in our water.
  • NSF 53: The NSF 53 is the most important of all certifications in the industry of water filtration as it directly pertains to health. It verifies the capability of the product to remove all the health hazards from the water.
  • NSF 58: Given only for RO systems, the NSF 58 certification simply signifies that the components of the RO filters are well within health regulations. Note that it doesn’t relate to the quality of the water in any sense but only to the materials the RO system is made of.
  • NSF 401: The NSF 401 certification verifies that the filtration system is capable of removing herbicides, pesticides, and pharmaceutical waste, as well as chemicals used in retardants and detergents.
Water Filters (Best to Worst)NSF Certification
Clearly FilteredNSF 42, 53, & 401
Aquasana OptimH2ONSF 42, 53, 58, & 401
Epic Smart ShieldNSF 42, 53, & 401
Waterdrop G3P800NSF 58
Frizzlife PD600Uncertified

Filtration Technology

Nowadays, reverse osmosis is the most conventional method for filtering water. However, it’s also responsible for eliminating beneficial minerals along the way, which usually forces brands to throw a remineralizer into the mix as well. Moreover, the water purified by RO systems is generally more acidic than it should be.

Therefore, leading innovators of the industry are in search of alternative methods that have similar contaminant removal success to RO while retaining beneficial minerals. In that sense, the Clearly Filtered (#1) and the Epic Smart Shield (#3) are exemplary systems. Both have developed their own unique filtration tech that’s a worthy alternative to RO.

Speaking of uniqueness, the Claryum tech of the Aquasana OptimH2O and the alkaline remineralizer of the Frizzlife PD600 are also worth mentioning. The Claryum is capable of removing unprecedented levels of sub-micron contaminants. The Frizzlife alkaline remineralizer, on the other hand, offers a better alternative to traditional remineralizers like that of the OptimH2O.

Water Filters (Best to Worst)Filtration Technology
Clearly FilteredA unique 3-stage filtration
Aquasana OptimH2ORO + Claryum + remineralizer
Epic Smart ShieldSingle carbon block filter
Waterdrop G3P800RO + UV sterilizer
Frizzlife PD600RO + alkaline remineralizer

Ease of Installation

Whether a DIYer can handle the installation and whether the owner’s manual clearly lays out the installation process are important aspects to consider when purchasing a water filtration system. After all, nobody wants to damage their plumbing due to a bad manual.

In that sense, the Clearly Filtered is the best item on our list, thanks to its detailed guide. Anyone with no prior plumbing knowledge can install it in under 15 minutes only with the help of a wrench.

The Aquasana OptimH2O, on the other hand, is the exact opposite of the Clearly Filtered. It requires someone with plumbing knowledge to install, and even with one, it might take longer than you’d like.

Water Filters (Best to Worst)Ease of Installation
Clearly FilteredDIY-level (>15 minutes)
Epic Smart ShieldDIY-level
Waterdrop G3P800DIY-level
Frizzlife PD600DIY-level
Aquasana OptimH2OPlumber required

Maintenance Requirements

Some systems have filters that need to be replaced more frequently than the others. Sometimes, even the filter replacement might require the presence of someone with plumbing experience.

Fortunately, though, none of the products on our list require such high maintenance. The Frizzlife PD600, in particular, blows the competition out of the water in this regard with its smart screen that tells you when to change which filter.

The Clearly Filtered and the Aquasana OptimH2O both have twist-off filters that can easily be replaced.

The only problem might lie with the Epic Smart Shield, whose filters cost almost as much as the whole system itself. However, should you register to their recycling program, you can get a new filter for every three used filters you send them.


A good warranty reflects the company’s trust in their product. Moreover, it can greatly reduce maintenance costs in the long run. So, it’s an important aspect of any purchase of a product that you aim to use for years, and water filtration systems are such products.

In that sense, the 100% lifetime warranty of the Epic Smart Shield and the limited lifetime warranty of the Clearly Filtered is the absolute best you can get. On the other hand, the unspecified warranty policy of the Waterdrop G3P800 and the limited one-year warranty of the Frizzlife PD600 might be causes for concern.

Water Filters (Best to Worst)Warranty
Epic Smart Shield100% lifetime warranty
Clearly FilteredLimited lifetime warranty
Aquasana OptimH2OTwo-year warranty
Frizzlife PD600Limited one-year warranty
Waterdrop G3P800Unspecified


Needless to say, a loaded price tag doesn’t always mean good performance. What we need to focus on instead is the value you get for the money.

All things considered, the best-value under-sink water filter is the Clearly Filtered. Although it’s not exactly super affordable, it has all the important NSF certifications, and it’s one of the most powerful filters among the independently tested ones.

Water Filters (Affordable to Expensive)Price
Epic Smart Shield$108.00
Aquasana OptimH2O$249.99
Frizzlife PD600$469.99
Clearly Filtered$495.00
Waterdrop G3P800$999.00

Frequently Asked Questions

We have covered all the important aspects you should consider when purchasing a new under sink filtration system. However, there are additional specific questions that we can answer.

Which under sink filter removes the most contaminants?

Although both Waterdrop and Frizzlife claim that their products can remove more than a thousand contaminants from the water, these claims aren’t supported by independently conducted tests. Nor are their filtration systems NSF-certified.

Among systems that have been independently tested and NSF-certified, the Clearly Filtered is the most powerful contaminant remover with 232+. Moreover, its removal success ratio is quite extraordinary.

What is the average price of an under the sink filter?

A decent under-the-sink filter will cost about $300-500. However, there are also affordable examples like the Epic Smart Shield. Although it only costs a bit north of $100, it still produces healthy water.

The Waterdrop G3P800, on the other hand, would fall on the other side of the spectrum. Its seven-stage filtration system is surely something to behold, and its price tag of almost $1,000 reflects that.

What does installation require?

Installation requirements of under-the-sink filtration systems vary wildly from one product to the next. Whereas the Clearly Filtered can easily be installed just with a wrench, the Aquasana OptimH2O requires professional plumbing.

More often than not, companies will include installation info on their websites and instruction manuals. It’s important to study them thoroughly in order not to mess up the plumbing and decrease the water quality while trying to improve it.

What is the average lifespan of the system?

A system can last for a lifetime, but its filters can’t.

You should replace the majority of carbon filters used in the making of home filtration systems once every six to twelve months. If the system is used in a commercial setting, you can do so every four to six months.

RO membranes and remineralizers, on the other hand, can serve their purpose for one to three years.

The best brands in the water filtration industry will let you know when the time for filter replacements comes. It’s best to heed their warnings.

Who are the best under sink water filter brands?

The most prominent and trustable names in the industry are as follows:

  • Clearly Filtered
  • Aquasana
  • Epic Filters
  • iSpring
  • Waterdrop
  • Frizzlife
  • APEC


To conclude, in almost all the important criteria we tested the products above, the Clearly Filtered leads the race. Its tested contaminant removal results are unmatched, it has all the important NSF certifications, and it’s quite efficient for its cost.

However, if you’re in the market for a traditional RO system with a tank, the Aquasana OptimH2O is the most reasonable option, thanks to its effectiveness and affordability. The Epic Smart Shield, on the other hand, is another affordable option, but it’s a portable and tankless one at that. If you don’t care about NSF certifications and want to get the best in water filtration technology, the Waterdrop and Frizzlife models both present good options. While the Waterdrop aims to remove as many contaminants as possible with its RO filter and UV sterilizer, the Frizzlife remineralizes water as no other system does.

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Scott Winfield
Scott Winfield
My name is Scott Winfield and researching and writing about water filters and other strategies to purify water has become my full time passion in recent years. I'm glad that you found our site and you can look forward to authoritative and well researched content here to help you get the best in water.
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