Best Under Sink Water Filter Reviews + Buyer’s Guide 2023

Author: Jason Hollow - Published: 2021/10/27 - Updated: 2023/01/05

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If you like the idea of a continuous supply of filtered water right from your kitchen faucet, an under sink water filter is destined to be your best buddy.

A high-quality system is capable of removing the harmful contaminants out of your drinking water. Plus, purchase, installation and maintenance are affordable and DIY-ready. Add ease of use and little space needs to this and you have the perfect home water filter.

But let’s clarify one thing: a poorly built under sink water filtration system will do nothing for your water. This makes it essential to base your buying decision on honest reviews and tested products.

This is why we test water filters regularly (literally our job!) to bring you the ones that are worth your hard-earned money.

So, here is our collection of the 8 best under sink water filters. Enjoy!


Best Under Sink Water Filters – Top Picks

Products Specs & Features Where to Buy
Best Overall
Clearly Filtered 3-Stage Under the Sink Water Filter System Clearly Filtered 3-Stage Under the Sink Water Filter System

Clearly Filtered 3-Stage

  • Price: $$$
  • Filter Stages: 3
  • Water: 80-85% of Initial Flow
  • NSF: 42, 53, 401
  • Best For: Most Comprehensive Tap and Well Water Filtration

Coupon Code (15% Off): WM15

Or read our review

Epic Smart Shield Under Sink Water Filter Epic Smart Shield Under Sink Water Filter

Epic Smart Shield


  • Price: $$
  • Filter Stages: 1
  • Water: 1.25 Gallons Per Minute
  • NSF: 42, 53, 401
  • Best For: City or Well Water Filtration on a Budget

Coupon Code (15% Off): MASTERZ

Or read our review

#1 Reverse Osmosis
Aquasana OptimH2O Reverse Osmosis + Claryum Under Sink Filter Aquasana OptimH2O Reverse Osmosis + Claryum Under Sink Filter

Aquasana OptimH2O


  • Price: $$
  • Filter Stages: 3
  • Water: 13.32 Gallons Per Day
  • NSF: 42, 53, 58, 401, P473
  • Best For: Remineralized RO Water

Or read our review

#1 Tankless RO
Waterdrop G3 Reverse Osmosis Water Filter System Waterdrop G3 Reverse Osmosis Water Filter System

Waterdrop G3

  • Price: $$$
  • Filter Stages: 3
  • Water: 0.3 Gallons Per Minute
  • NSF: 58
  • Best For: RO Purified Tap Water

Or read our review

Best Under Sink Water Filter Reviews

The order of the following under sink water filter reviews is deliberate. Our favorite products are at the top.

1. Best Overall: Clearly Filtered 3-Stage Under the Sink Water Filter System

Coupon Code (15% Off): WM15

In our opinion, the best under sink water filter in 2023 is the Clearly Filtered 3-Stage. What sets it apart from all others is that it has been tested to NSF standards to remove more than 230 toxic contaminants, including lead and other heavy metals, water-borne bacteria, viruses, hormones, PFOA, PFOS, etc.

No wonder we haven’t come across any conventional under sink water filter that can remove so many harmful contaminants. That’s a major WIN!

Besides the exceptional filtration capability of the Clearly Filtered, installation and maintenance is as easy as flicking a light switch. And the biggest victory of the brand is evident through the steeping number of satisfied customers.

Clearly Filtered 3-Stage Under-the-Sink Water Filter System


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Main Specs

  • Price: $$$
  • Filter stages: 3
  • Flow rate: Feed water pressure minus 15-20%
  • Filtration capacity: 2,000 gallons
  • Estimated annual filter replacement cost: $400
  • NSF: 42, 53, 401
  • Best for: The Clearly Filtered 3-stage is best for under sink water filtration.

Clearly Filtered 3-Stage Under the Sink Water Filter System a Clearly Filtered 3-Stage Under the Sink Water Filter System b


  • The first stage of the CF 3-Stage sports granular activated carbon filter media that removes volatile organic compounds, chlorine (98.6%), chloramines (95.3%) and other chemicals that may also alter the taste and odor of water.
  • The second stage features a proprietary blend of filtration media that does the heavy lifting. As water passes through the stage, it is freed from lead (99.9%), chromium 6 (99.4%), pesticides, herbicides, radiological elements, PFAS and much more.
  • The final filter stage is where the most difficult to remove contaminants are eliminated. The media reduces fluoride (99.5%) and arsenic (94.3%) amongst a few other which could expose your family to a host of illnesses.
  • The contaminant removal claims made by Clearly Filtered are not mere statements. Their under-the-sink sink system is rigorously tested by a certified laboratory that certifies it withholds NSF standards 42, 53 and 401.
  • Unlike RO systems, the CF 3-Stage retains all healthy minerals, so your water is not considered “dead”.
  • Installation is extremely quick and convenient – especially for rentals – thanks to the inline design and non-permanent setup.
  • Maintenance is extremely easy and takes no longer than 15 minutes.
  • Filters last for a year.
  • Thanks to premium quality stainless steel inlet and outlet ports, the CF under sink filter system will last for years and years on end.
  • Did we mention a 30-day no-questions-asked policy that means you have nothing to lose and everything to gain? If you don’t like the water filter, you can return it for a full refund within a month.
  • The lifetime warranty ensures you never need to pay any repair cost at all.


  • The unit is priced higher than most competitors on the market. Regardless, the steep price is justified by the premium quality materials and state-of-the-art Affinity Filtration technology.
  • Similarly, the cost of replacement filters is also higher. Nevertheless, if you shop in bundles and subscribe to the Clearly Filtered VIP program, you’d be eligible for discounts and free shipping.
  • One issue that some people may find problematic is the drop in water pressure by roughly 15%. To us, however, this is neither troublesome nor did it worsens with time as filters aged.

Or check out our complete CF 3-Stage review

2. Best for Comprehensive Filtration on Low Budget: Epic Smart Shield Under Sink Water Filter

Coupon Code (15% Off): MASTERZ

If you are looking for a premium quality under sink water filtration system, the Epic Smart Shield could also be your go-to – apart from the Clearly Filtered reviewed above. It’s great for people who want good quality on a budget. Besides doing a great job at filtering municipal water, the Epic Smart Shield is also perfect for those on a well water supply.

It’s certified to remove over 70 plus tap water contaminants that make your water smell terrible and compromise the health of your loved ones.

What’s best is the value for money this system provides the customer. Although it costs way less than many other under sink water filters on the market, it outperforms most competitors.

Epic Smart Shield Under Sink Water Filter


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Main Specs

  • Price: $$
  • Filter stages: 1
  • Flow rate: 1.25 gpm
  • Filtration capacity: 651 gallons or 1 year
  • Estimated annual filter replacement cost: $140
  • NSF: 42, 53, 401
  • Best for: The Epic Smart is ideal for broad contaminant removal, particularly on a budget.


  • The Epic Smart Shield under sink filtration system uses a solid carbon block design featuring activated coconut shell carbon filtration media.
  • The robust single-stage under sink water filter removes up to 99.9% of common tap water contaminants, including chlorine/chloramine, Glyphosate, microplastics, PFOA, radioactive materials, fluoride, lead, asbestos, mercury, and E. Coli.
  • We don’t just believe claims and always rely on testing and certifications. That’s why we are happy to report the Epic Smart Shield is tested against NSF/ANSI standard 42, 53 and 401.
  • Households using highly sedimented well water are advised to install an additional 5-micron sediment pre-filter to prevent premature choking. Pre-treatment also ensures a longer service life for the main filter cartridge.
  • The smart design ensures a quick DIY installation. Thanks to the inline setup and quick connect fittings, the installation process is quick and doesn’t necessitate professional help. You save hundreds of dollars that would otherwise be needed to hire a pro.
  • All supplies to install the unit are included in the installation kit, so you don’t have to run back and forth to hardware shops.
  • Even though the design is inline, you have the option to purchase an extra faucet.
  • Filters last for at least a year and have a filtration capacity of 651 gallons.
  • Maintenance is also cheap at ~$140 per cartridge. In addition, if you subscribe to the Clean Water Club, you can save 20% on replacement filters.
  • Each filter is 100% sustainable and is recycled by the company itself. Upon returning three used filter cartridges, you can get one absolutely free.
  • Inexpensive compared to other filtration systems offering similar performance.
  • Consumers rave about excellent customer support staff, making installation and maintenance even easier, especially for new owners.
  • Quote from Epic Water Filters website: “If you are not 100% satisfied (…) you may return the merchandise to us for a full, 100% refund (…)”.


  • Since the flow rate is 1.25 gpm, a few users noticed a drop in water pressure. Regardless, we don’t think it should be a big issue for everyone.

3. Best for Remineralized Water: Aquasana OptimH2O Reverse Osmosis + Claryum Under Sink Filter

For people looking for an under sink reverse osmosis water filter system, the Aquasana OptimH2O is a perfect choice. Besides removing a host of toxic contaminants from the water (courtesy of a robust RO membrane), the Aquasana OptimH2O also adds healthy minerals for better-tasting drinking water.

The process of remineralization tremendously improves the flavor of water and balances its pH level. In a nutshell, it eliminates the number one problem with RO water, making it wholesome and nutritious again.

Aquasana OptimH2O Reverse Osmosis + Claryum Under Sink Filter


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Main Specs

  • Price: $$
  • Filter stages: 3
  • Water production: 13.32 gallons daily
  • Filtration capacity: 6-12 months
  • Estimated annual filter replacement cost: $200
  • NSF-Certified: 42, 53, 58, 401, P473
  • Best for: The Aquasana OptimH2O reverse osmosis system is best for remineralized RO water.


  • The 3-stage filtration process features activated carbon, a reverse osmosis membrane[1], and a Claryum filter.
  • As water passes through the first stage, carbon adsorbs chemicals such as chlorine and larger particles.
  • Next in line is the RO membrane that rejects hundreds of microorganisms, heavy metals, inorganic compounds, etc.
  • Then, the Claryum filter, a combination of activated and catalytic carbon, reduces remaining water contaminants like chlorine, pesticides, chloramine, fluoride and few heavy metals.
  • Finally, the water passes through a remineralization chamber where healthy minerals like calcium and magnesium are added back to your water. Improved taste!
  • Certified to NSF 42, 53, 58, 401 and P473.
  • The manufacturer guarantees a 13.32-gallon filtration capacity per day, which is more than enough for a big-sized family (6+ members).
  • Installation is quick and beginner-friendly. All parts are included in the install kit provided with the unit.
  • Similarly, maintenance is also easy and doesn’t take a lot of time. The carbon filters last 6 months, while the RO membrane lasts for 12.
  • We estimate annual maintenance costs at about $200. Subscribe to the replacement filter’s program for further discounts.
  • You receive a 90-day money-back guarantee for peace of mind.
  • A 2-year warranty also ensures you are safeguarded from repair costs for at least a few years.


  • Sadly, we have read a few negative reviews which highlight leakages and poor quality of some of the materials.
  • Some people also complain of a slow flow rate.
  • As with all RO systems, the unit produces wastewater.

Or read our complete Aquasana RO review

4. Best for RO Purified City Water: Waterdrop G3 Reverse Osmosis Water Filter System

For people who have minimal space under the sink, the Waterdrop G3 under sink reverse osmosis system is the ideal choice.

Unlike most RO systems, the unit does not need a separate water storage tank. Instead, it can filter the water on demand which saves a lot of space. And thanks to the robust RO membrane, modern design, and ability to filter out a wide range of contaminants, the unit has caught our eyes and has hundreds of satisfied customers.

Waterdrop G3 Reverse Osmosis Water Filter System


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Main Specs

  • Price: $$$
  • Filter stages: 3
  • Flow rate: 0.3 gpm
  • Filtration capacity: 550-2,200 gallons
  • Estimated annual cost for new filters: $120
  • NSF: 58
  • Best for: The Waterdrop G3 is ideal for RO purified city water.

Waterdrop G3 Reverse Osmosis Water Filter System a


  • The simple, tankless unit features a 3-stage filtration process.
  • The first stage is a composite filter that combines a sediment filter with activated carbon to remove large undissolved particles and chemicals like chlorine.
  • Next is the RO membrane that rejects almost 99.9% of hundreds of contaminants, including heavy metals, salts, bacteria, viruses, and cysts.
  • Finally, a carbon block filter polishes the water by removing odors and taste-altering chemicals.
  • Certified by NSF 58 to reject Total Dissolved Solids.
  • An inbuilt pump increases the flow rate to almost 0.3 gallons per minute.
  • The water pressure pump also brings down the wastewater ratio to 1:1. The standard ratio of wastewater to purified water is 4:1 in regular RO systems.
  • All materials are BPA-free to ensure safety.
  • The installation process is quick and DIY-friendly. No need to hire plumbers; thus, you save a considerable amount upfront.
  • Filter replacements are quick and easy. Yearly maintenance costs are about $120. That’s relatively inexpensive compared to other under sink RO systems.
  • An inbuilt TDS meter shows the TDS level. If you find the TDS level going up, it’s a sign that you need to change your filters.[2]
  • The smart LED on the faucet and the system itself also signify when it’s time to replace a filter. Therefore, you are never short of clean purified water.
  • The well-built unit ensures no leakages.
  • You receive a 30-day guarantee to test the under sink water filter. Then, if you don’t like it, you can return it for a full refund – no questions asked.
  • A 1-year warranty offers you peace of mind.


  • Costs more than other RO systems on the market.
  • Only 1 NSF certification.
  • Doesn’t mention specific reduction rates of contaminants.
  • Lots of complaints regarding the TDS indicator, which doesn’t show exact values.

Or view our complete Waterdrop G3 review

5. Best for NSF-Certified Filtration on a Budget: Aquasana Claryum 3-Stage Max Flow Under Sink Water Filter System

For those who want a long-lasting and robust multi-stage under sink water filtering system, the Aquasana Claryum 3-Stage Max Flow a.k.a. AQ-5300+ is an excellent choice.

It combines the power of catalytic and activated block carbon to eliminate hard-to-remove disinfectants like chloramine and much more. In addition, the large size of the Aquasana max flow ensures longer service life which makes it stand out from many competitors.

Besides the high quality of the filter, we love how Aquasana is a household name due to its excellent customer support. The staff at Aquasana go out of their way to guarantee customer satisfaction.

Aquasana Claryum 3-Stage Max Flow Under Sink Water Filter System


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Main Specs

  • Price: $$
  • Filter stages: 3
  • Flow rate: 0.72 gpm
  • Filtration capacity: 800 gallons
  • Estimated annual cost for new filters: $160
  • NSF-Certified: 42, 53, 401, P473
  • Best for: The Aquasana Max Flow is best for NSF-certified filtration on a budget.


  • The 3-stage system combines a sediment pre-filter, a carbon filter, and catalytic carbon to reduce up to 99% of 77 contaminants. Certified for removal are disinfectants and other chemicals, cysts, heavy metals like lead, BPA, VOCs and pharmaceuticals.
  • The first is the sediment filter stage that removes larger particles like sand, rust, dust, clay and silt.
  • Next, the regular activated carbon removes chemicals and a few heavy metals.
  • Finally, catalytic carbon reduces/removes chloramine and residual heavy metals.
  • Certified to NSF standards 42, 53, 401 and P473.
  • If you are on a budget, you can also select one of the other two under counter water filter models, Aquasana AQ- 5200 or AQ-5300. Keep in mind that all three units have the same NSF certifications and contaminant reduction rates as the Aquasana Max Flow. The only difference is the AQ-5300 and the Max Flow has an additional sediment pre-filter. What’s more? The Max Flow has a higher filtration capacity and flow rate.
  • The system uses a dedicated faucet to make sure not a single drop of filtered water goes down the drain wasted. Select from any of the three lead-free faucet designs/finishes to blend in with your kitchen’s interior. Our favorite is brushed nickel!
  • Easy to install? You bet! Quick and DIY-friendly, too. All necessary parts and supplies are included in the installation kit. All you need to do is follow the manual or watch the comprehensive instruction videos on YouTube, and you’ll be done in under an hour.
  • Maintenance is easy and costs around $160 annually.
  • Filters last for at least six months. Sooner replacements may be needed if the water supply is too hard/contaminated.
  • Thanks to light signals and audible alarms, it’s virtually impossible to miss filter changes. You can also connect the Aquasana Max Flow to your smartphone through the Aquasana app. It’s a one-stop solution to keep track of your filter life and order new cartridges.
  • You receive a 1-year limited warranty.


  • For a non-RO under sink filter system, annual maintenance charges are rather steep. You can subscribe to the Water For Life program for discounts, though.
  • Even though Aquasana prides itself on consumer satisfaction, many people have reported issues highlighting substandard materials and manufacturing. Some users pointed out loose tubing, flimsy filter housings, short-lived faucets and constant leakages.
  • We have also read about poor water pressure.

6. Best for Affordable Multi-Stage Filtration: Frizzlife SK99 3-Stage Under Sink Water Filter System

Are you struggling with PFAS, lead and/or cysts? Then the Frizzlife SK99 is a great budget option for you, being NSF standard 53 certified for exactly these contaminants.

Frizzlife SK99 3-Stage Under Sink Water Filter System


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Main Specs

  • Price: $$
  • Filter stages: 3
  • Flow rate: 2.0 gpm
  • Filtration capacity depends on filter stage
    • 1st: 3-6 months
    • 2nd: 8-12 months
    • 3rd: 12-18 months
  • Estimated annual cost for new filters: $80
  • NSF: 42, 53
  • Best for: The Frizzlife SK99 3-Stage under sink water filter system is best for multi-stage filtration on a budget.

Frizzlife SK99 3-Stage Under Sink Water Filter System b


  • The 3 filter stages – in stage one we have a sediment filter followed by two carbon block filters of different micron ratings – reduce up to 99% of dirt, lead particles, arsenic, chlorine/chloramine, fluoride, volatile organic compounds and more.
  • The filtering process is tested and certified by IAMPO against NSF/ANSI standards 42 and 53.
  • All the beneficial minerals remain in the water.
  • Braided hoses are much more durable than plastic tubing.
  • It’s all included in the DIY installation kit. Setup takes less than 15 minutes if you follow the instruction video.
  • Replacement filters are affordable and long-lasting.


  • People mostly complained about not noticing a difference in filtered water taste.

7. Best for Lowest Maintenance: CuZn UC-200 Under Counter Water Filter

A somewhat hidden gem, the CuZn UC-200 under sink water filter makes your water taste as if it came directly from a natural spring.

So, if you are blessed with a relatively clean water supply and the only complaint you have with your tap water is slightly foul smell and weird taste, you should consider giving the CuZn UC-200 a chance. We are sure you won’t be disappointed.

CuZn UC-200 Under Counter Water Filter


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Main Specs

  • Price: $$
  • Filter stages: 3
  • Filtration capacity: 50,000 gallons or 5 years
  • Estimated annual cost for new filters: –
  • NSF: 42
  • Best for: The CuZn UC-200 system is best for those looking for low maintenance.


  • Manufactured in the USA.
  • The 3-stage under sink filter system combines a sub-micron sediment filter with activated carbon to remove numerous organic and inorganic contaminants, including chlorine, lead, herbicides, pesticides and sulfur.
  • As water passes through the first filter stage, sub-micron sediment filtration removes undissolved solids like rust, sand, silt and clay.
  • The second and third stages feature carbon to improve the aesthetics of your water by removing odor-causing chemicals.
  • What’s best is that the filter is bacteriostatic. In simple terms, bacteria or mold cannot grow inside the unit. Compared to standard carbon filters, this unit will last you way longer without fouling.
  • NSF certified against standard 42, which covers a filters’ ability to remove aesthetic contaminants.
  • Installation is quick and straightforward and can easily be done by yourself. In addition, you will receive the necessary fittings in the package to make the process even easier.
  • If you do not have the desired adapters, you can reach out to customer service, who will gladly send you all the necessary fittings.
  • Just watch the complete tutorial video on the company’s website for clear instructions on installing the unit.
  • What’s more is that there is no maintenance required at all. You get a filtration capacity of 50,000 gallons or five years, whatever comes first.
  • A 90-day money-back guarantee ensures you have nothing to lose. If you do not like the product, you can claim a full refund.
  • A 2-year warranty is also part of the deal.


  • Some people experienced leakages in the unit. They are quite annoying since repairs are complicated due to the design.
  • Others noticed black grains in their otherwise clean water. We’re sure that’s carbon media breaking down and entering the water.

8. Best for Lowest Operation Cost: Culligan US 1, US 3 and US 4 EZ-Change Sink Drinking Water Filtration Systems

For those who want the support of a trusted brand along with a decent price tag, the Culligan EZ range is a great choice. The series features three under sink filters that are interchangeable depending on the quality of your source water.

The US 1 targets chlorine but is pretty much ineffective against all other contaminants. In contrast, the Culligan US 3 and US 4 feature more sophisticated filtration capabilities and target various other toxic pollutants that might be in your water.

We love the fact that Culligan has customized its filter range according to the needs of people. For example, if you are only concerned with poor tasting and weird-smelling water, the US 1 system should be your first choice. However, you can use the US 3 or US 4 cartridge with the same unit if you want more robust purification.

Culligan US 1 EZ-Change Sink Drinking Water Filtration Systems


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Main Specs

  • Price: $
  • Filter stages: 1
  • Flow rate: 0.5 gpm
  • Filtration capacity and NSF certifications depend on which filter model you choose:
    • US 1: 3,000 gallons, NSF 42
    • US 3: 500 gallons, NSF 42 & 53
    • US 4: 500 gallons, NSF 42, 53, 401
  • Estimated annual cost for new filters: $20-120
  • Best for: The Culligan US 1, US 3 and US 4 EZ-Change systems are ideal for anyone wanting a low cost of operation.


  • The single-stage filters can be used with any of the following cartridges. We advise testing your water to avoid guessing which one you need. If you ask us, we definitely recommend the US 4 for the most thorough filtration.
  • US 1: It removes chlorine and few particulates (Class III).
  • US 3: It eliminates chlorine, lead, finer particles, cysts, lindane and turbidity.
  • US 4: It targets a wide range of contaminants, including disinfectants, fine particulates, cysts, lead, mercury, MTBE’s and volatile organic compounds.
  • All US EZ-Change systems are NSF-certified against varying standards: 42, 53 and 401.
  • We love the compact design, which means the filters take up less space inside the cabinet and are also easy to maintain.
  • A dedicated, lead-free faucet is also included with the package.
  • No need to dial your plumber for the installation of Culligan water filters. All you need is a few fittings, a spare afternoon and determination. We recommend reading the manual thoroughly and asking a friend for help to make setup easier.
  • Maintenance is as simple as ABC. Just twist the old cartridge out and slide in a new one without turning off the main water supply. Cost? Less than $100 yearly or slightly more depending on the filter model you choose.
  • A 2-year limited warranty is good enough to seal the deal.


  • The faucet included in the package isn’t very high quality and is prone to breakage with regular wear and tear.
  • Some people complained about leakages in the under sink water filter.
  • Half a gallon water flow at 60 psi water pressure is not exactly high. Many people found the poor flow rate to be a deal-breaker.

Under Sink Water Filtration System Comparison Chart

How do the best under sink water filters of 2023 perform when directly compared to each other?

System $$$ Stages Water Flow Filter Capacity Yearly Cost NSF/ANSI Best For Details
Clearly Filtered Undersink Filter $$$ 3 80-85% of Initial 2,000 gal $400 42, 53, 401 Best Under Counter Water Filter Overall Highest Quality Water, Stainless Steel Water Lines, Same Faucet
Epic Smart Shield $$ 1 1.25 gpm 651 gal $140 42, 53, 401 Best for Broad Contaminant Removal on a Budget Eco-Friendly, No Need to Install Second Faucet
Aquasana OptimH2O RO System $$ 3 13.32 gallons daily 6-12 mos $200 42, 53, 58, 401, P473 Best for Remineralized RO Water Reverse Osmosis Filter Produces Pure Water, Uses Remineralization Filter, Own Faucet
Waterdrop G3 RO System $$$ 3 0.3 gpm 550-2,200 gal $120 58 Best for RO Purified City Water Based on Reverse Osmosis (RO) for Pure Water, Own Faucet
Aquasana Max Flow $$ 3 0.72 gpm 800 gal $160 42, 53, 401, P473 Best for NSF-Certified Filtration Own Faucet
Frizzlife SK99 $$ 3 2.0 gpm 3-18 mos $80 42, 53 Best for Multi-Stage Filtration on a Budget Uses Sub-Micron Filtration for Removing Contaminants, Filter May Remove Bacteria, Same Faucet
CuZn UC-200 Undersink Filter $$ 3 ? 50,000 gal 42 Best for Low Maintenance Easier to Install, Same Faucet
Culligan US 1, 3, 4 EZ-Change $ 1 0.5 gpm 500-3,000 gal $20-120 42, 53 Best for Lowest Operating Cost Filters Are Designed to Last Long and Be Interchangeable, Own Faucet

Buyer’s Guide – How to Buy an Under Sink Water Filter (+ How We Tested)

Here’s our buying guide with everything you need to know about how to buy the best under sink water filter systems.

Filter Technology

Typically, under sink water filters feature one or more of these types of filter media.

  • Catalytic/activated carbon
  • Ion exchange resin
  • KDF
  • Iron filter media
  • Ceramic

In addition, there’s RO water purification and ultraviolet light treatment.

What type of under sink filter you should buy will largely depend on the quality of your source water. For instance, an activated carbon filter is a good option if your water is contaminated with chlorine and chemicals. In contrast, a reverse osmosis system should be your first choice if you are using water with multiple types of impurities: heavy metals, salts, bacteria, etc.

Since no filter can eliminate all contaminants, you must know what you want to remove beforehand. It’s wise to test your water using DIY test kits or send a sample to a certified laboratory.

Filtration Stages

The rule of the thumb is that the more filter stages an under sink water filtration system has, the better it’s suited to target a wide range of contaminants. In this guide, you will find single-stage under sink water filters as well as multi-stage systems.

Multi-stage mostly use sediment filters as pre-filters that protect the subsequent filters from clogging too soon. So, you can go longer between replacements. Carbon is used to remove chemicals. KDF-55 filtration media prevents bacterial contamination.[3] And so on.

However, multiple filter stages may translate to higher maintenance costs over time. They also pose more restrictions on the flow of water (more about this below).

Water Pressure and Flow

trickling faucet

Under sink filters’ flow rate is measured in gallons per minute (gpm). It’s important to understand that a standard faucet without any filter supplies water at around 2.0 gpm, but that level should not be expected out of any good filtration system.

You see, every turn, bend, limitation, and media will restrict the flow of water. Oddly enough, slow filtration is beneficial because it means water spends more time with the filter element.

Let’s say your water swishes right through the filter media, it won’t absorb as many contaminants. But obviously, nobody likes to stand for ten minutes on the faucet while filling a pitcher either.

You must aim for a perfect balance of contaminant removal and speed. For reference, the Aquasana AQ- 5300, which offers meticulous purification, provides a flow rate of 0.5 gpm. Remember, as filters clog, there will be a further drop in flow rate and water pressure, so keep that in mind as well.

NSF Certifications

We always recommend buying any type of filter with NSF/ANSI testing and certifications. In fact, the logical course of action when shortlisting your options is to first look for NSF standards.

Broadly speaking, all under sink water filters are constructed for different purposes. Some focus on the removal of sediment, while others improve water aesthetics. To free yourself from all the technical jargon, simply look for:

  • Standard 42: The standard addresses a water filter’s ability to remove chlorine taste and odor as well as particulate matter.
  • Standard 53: It ensures that the filter can remove a significant amount of a specific contaminant with a ‘health effect’.
  • Standard 58: The standard establishes minimum requirements for material safety. It is only applicable to RO systems.
  • Standard 401: This certification focuses on ‘emerging compounds’ and incidental contamination of public and private water supplies.

The Water Quality Association and other institutions test and certify products against NSF and EPA standards.

Under Sink Water Filter Installation

Unlike whole house water filters, you can easily install an under sink water filter yourself – provided you have basic plumbing knowledge. Neither do you need fancy tools, nor do you need to make elaborate permanent changes to your piping.

Installation can be a little tricky for a system that comes with a dedicated faucet, however. Installing a new faucet typically involves drilling into your countertop, which is not always easy. If you already have a spare hole used previously for a soap dispenser etc., then you should consider yourself lucky. Your work will be cut short.

If you need a new hole altogether, we would advise asking for help depending on your skills, or you might end up damaging your marble, quartz, or granite.

Nevertheless, a dedicated filtered water dispenser will help cut down maintenance costs in the long run. This is because you won’t waste filtered water while doing dishes or for anything apart from cooking and drinking.

Even if you require professional help, a plumber or technician should charge you no more than $200 for the job, which takes little more than half an hour.

Tip: Always finalize the price before handing out the job, which prevents arguments later on.

Maintenance and Filter Life

The chief reason to opt for an under sink filtration system – rather than a filter pitcher for example – is its prolonged service life. Most can handle a good quantity of water and last for a minimum of 6 months, provided you use up to 3 gallons per day and your water doesn’t have any severe contamination.

With that said, it’s not guaranteed that your under sink filter will ever reach its actual filtration capacity in terms of gallons. This is because the longer you use a filter, the higher the chance is for bacteria to grow inside the filter media fouling the water.

Suppose you buy a system that has a serviceable life of 2,000 gallons of filtered water. With average usage (3 gallons daily), in theory you could use it for 2 years straight. Sadly, you will likely be disposing of the cartridge much sooner due to buildup.

That said, maintaining under sink filters is child’s play. If you are regular with your filter replacements, you won’t find much trouble. You twist the housing, slide out the old cartridge, and slide in a new one.

Space Requirements

While most under sink filter systems are not massive, you might want to consider their size if you have minimal space in your kitchen.

The difference in space needed is especially notable between RO and all other under sink systems. Since RO filters feature very slow filtration, water is stored in a storage tank. Therefore, RO systems take up double the space compared to regular under sink filters.


In the year of purchase, the total annual cost of under sink water filters is calculated by adding the initial cost plus maintenance filter expenses.

So even if a unit is cheaper upfront, it’s not a good idea to invest in it right away without estimating filter cartridge life and cost.

What is an Under Sink Water Filter?

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If you go several years down the memory lane, you probably wouldn’t be sold to the idea of water filtration at home. After all, you live in the USA, and your city must provide you with clean drinking water.

However, with the rise in incidents of hazardous contamination (think Flint[4]) especially in the past decade, we are led to believe otherwise. This is where an under sink water filter for your home comes to the rescue.

It’s a point-of-use filtration system that usually purifies municipal water on demand. Since you can treat unlimited water at any time, under sink filter systems are a favorite amongst big families.

Due to their compact size, they can easily fit inside any cupboard. Moreover, a good quality filter ensures your water is free of unpleasant odors, foul tastes, and slimy texture. High-quality units can also remove a wide range of contaminants that pose a health risk.

Under Sink Water Filter Types and How They Work

All under sink water filtration systems use different technologies and a varying number of filter stages. For example, you can buy a single-stage sediment filter, a multi-stage carbon-based filter, or a sophisticated RO system one depending on the quality of your feed water. Here we discuss the types of under sink filters in detail.

Simple Under Sink Water Filters

These simple units feature a single-stage purification system. Therefore, if your household has a specific water problem, you can choose to treat only that one issue using a single-stage filter.

Multi-Stage Systems

Multi-stage units feature multiple types of filtration or filter media, including mechanical, chemical, ion exchange, or absorption filters. Each one of these focuses on a different water issue, and many conventional filters use a combination of these methods to perform thorough filtration.

Reverse Osmosis Systems

Under sink reverse osmosis systems are the ultimate. Amongst other filter stages, they use an RO membrane to remove up to 99.9% of literally hundreds of water contaminants that almost no other filter type can even come close to. However, nutritionists sometimes refer to RO water as “dead water” since it’s also deprived of healthy minerals.

RO systems feature a storage tank and come with a dedicated faucet. They also need a drain line connection since the process produces wastewater.

Inline vs. Dedicated Water Dispenser

Under counter water filters either come with an extra faucet or can be attached to the existing one of your kitchen sink (inline). That’s the only difference between the two.

With an inline system, you can’t shift between filtered and unfiltered water on demand. Whether you are doing the dishes or any of the million other household chores, you end up using filtered water.

If you want to use clean water only some of the time and like to have a separate faucet altogether to avoid exhausting your filter cartridges sooner, then the dedicated faucet system may be a good option.

Under Sink Water Filtering System Pros and Cons

Let’s go through a few key pros and cons of having an under counter filter system at home.


  • They bring about a considerable improvement in the taste and smell of water.
  • Secondly, they can remove an arsenal of contaminants that pose serious health risks.
  • Under sink water filtration systems are inexpensive when compared to whole house filters or the notorious bottled water.
  • Installation is quick and straightforward.
  • Maintenance is also super easy. Filters usually need to be replaced twice a year at maximum.


  • They only treat water at one faucet.
  • Under sink systems with a dedicated dispenser require drilling the countertop, which may require professional help.

Who Needs Under Sink Water Filters?

Do you hate the smell and taste of your drinking water? Are you tired of bottled water draining your pocket? Or perhaps your fridge filter isn’t able to deal with numerous contaminants that are making your family sick.

If your lips twirled into a big yes to any of these questions, you should go ahead and make the purchase.

Good under sink water filters check all the boxes. For a start, they make water fresh and crisp. Secondly, they produce water that is 300 times cheaper than bottled water.[5] And finally, they do a great job at eliminating and reducing dangerous contaminants.

How to Install an Under Counter Water Filter in the Kitchen

Here is a short guide to help you install an under sink filter yourself. Don’t worry; it’s a beginner-friendly project and doesn’t require any power tools.

  1. Turn off the valve for cold water supply.
  2. Then, disconnect the cold water line.
  3. Next, connect the inlet port to the cold water line. Similarly, the outlet port must be connected to the existing faucet.
  4. Mount the filter if you want.
  5. Open the cold water valve and flush the unit for a few minutes.
  6. Finally, enjoy filtered water.

under sink water filter being installed


Depending on the type used, under sink water filters should be replaced every 6 months to a year.

Thankfully, you don’t need to hire a plumber or pay excessive service charges. All you need is a few minutes of your time, along with a housing wrench.

If your filter is badly stuck, you may need to use a few tricks like heating it, hitting it with a rubber mallet, or using a metal or strap wrench to get it moving.

Once you’ve removed the sump from the cap, check the O-ring and lubricate or replace it if need be. Then give the housing a quick rinse with soapy water and slide in the new filter cartridge.

Finally, twist back the filter housing and enjoy clean water.

It goes without saying, all replacements must be made after turning off feed water.

Under Sink vs. Countertop Water Filters

It’s s always a long debate when it comes to deciding between under sink or countertop filters. So allow us to end the debate once and for all.

In a nutshell, both systems host more similarities than differences and fall in the same price category. Nevertheless, we are fans of under sink water filter systems because they (the good ones) are sturdier and run longer between replacements.

Also, those who don’t want to compromise the look of their kitchen should opt for an under sink system (out of plain sight). But if you want minimal installation, you can go ahead with a countertop water filter.

Anyway, here is a short guide to help you make the decision based on your needs.


Here are fundamental similarities between under sink and countertop water filters.

1. The Filtration Process

Most of the time, the filter process is pretty much similar, featuring either single stage or multiple stage water filtration. The filtration technologies are also the same. In fact, you can find carbon, KDF, ion exchange, reverse osmosis (RO), etc. in both countertop and under sink filters.

2. Filter Capacity

There are so many models in the market for both kinds of treatment systems that you can easily find the same filtration capacity in both units.

3. Filter Replacements

Installed under the sink, you need to get down on your knees to replace filters. Other than that, there is precisely no difference in replacement techniques.


Here is what differentiates the two types of filters.

1. Size

Since countertop units are designed to be kept on the counter, they are generally more compact.

On the other hand, under sink filters can be a little bulky comparatively.

2. Ease of Installation

Countertop water filters can be attached directly to the existing faucet and need no installation. They can easily be hooked up in less than 5 minutes and require no setup whatsoever.

In contrast, an under sink system needs to be hooked into the cold water line. And then filtered drinking water either flows out of the dedicated faucet or the original faucet.

You need to break in the water line and then attach the inlet tubing. Then direct the outlet pipe to the faucet.

Frequently Asked Questions (FAQ)

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How do you choose an under sink water filtering system?

Consider the level of contamination in your source water, and then look for an under sink filter that uses the right technology to solve your water problem. Make sure you look for NSF certifications or testing to ensure the under sink filtration system removes a majority of the contaminants.

Then, compare the flow rate and average costs per year incurred to maintain the system.

Should I invest in an under sink filter?

Yes, yes, and yes! Under sink water filter systems are exceptional units perfect for households that go through 2-3 gallons of water or more every day.

How often should you change an under sink water filter cartridge?

Typically, you should change cartridges every six months or so. However, if your water quality is too bad or you consume more water daily, you might need replacements sooner than that. Just look for obvious signs like poor water flow and smelly, bad tasting water.

Also remember, some systems have a service life of thousands of gallons while others exhaust after treating a few hundred.

How do you connect an under-the-sink filtration system to your kitchen sink?

These filters are easy to install and set up. Just mount your system inside the cabinet and then connect the inlet hose to the cold water supply. The outlet port connects with the faucet on top.

If your system comes with a dedicated faucet, you will need to do some drilling which requires expert knowledge.

How do you clean an under sink filter system?

All you need is soap and water to clean under sink filters. We advise cleaning your system every time you replace the cartridges.

If you notice nasty green algae or mold, use an NSF-certified sanitizer to deep clean the unit.


An under sink water filter can make a great addition to your home. But, make sure to choose one suited for your water quality. Our favorite is the Clearly Filtered. If you are on a budget check the Epic Smart Shield. As for the #1 under sink RO system, we recommend the Aquasana OptimH2O.

If you have questions about these or any other under sink water filter systems please leave a comment below!

Further Reading

More Under Sink Water Filters Reviewed


Meet Jason Hollow

Jason Hollow Jason is the founder of Water Masterz and head of content creation. After six years in the industry, he has tremendous knowledge and first-hand experience on all things related to water treatment.

His credo: Not a single American should have to drink unhealthy water at home.

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