The 6 Best Under-Sink Water Filters: Reviewed and Compared (2024)

I teamed up with our in-house water expert, James Layton, to evaluate 25 under-sink water filters using our carefully cultivated research design. We engaged manufacturers, customers, and industry experts to narrow down our top picks, compiling and comparing data and reading every user manual and warranty. 

Based on our research, the Waterdrop G3P800 is the best overall under-sink water filtration system. But if you’re looking for the best low-budget under-sink system or the best warranty, there’s an under-sink water filter for you too. If you’re new to under-sink water filters, check out our buyer’s guide below. Here are the best under-sink filtration systems.

Best Overall: Waterdrop G3P800 9.3/10

The Waterdrop G3P800 tankless reverse osmosis system is the best under-sink water filter because it removes over 1,000 contaminants from tap water, including bacteria and viruses, provides real-time water quality data, and leaves room for under-sink storage.

PROS

The Waterdrop G3P800 offers the highest standards for under-the-sink water filtration. Here are five reasons why:

Pro 1/5: Comprehensive contaminant removal

The first thing you’ll appreciate about the Waterdrop G3P800 is its comprehensive filtration process that tackles 99.99% of contaminants. A filter with the fanciest features won’t make a lick of difference if it doesn’t do what it’s meant to do.

At the heart of the Waterdrop G3P800’s effectiveness is its multistage filtration, which combines a sediment filter, activated carbon filter, reverse osmosis, ultraviolet purification, and remineralization. These combined stages improve water taste and odor and remove chlorine, fluoride, PFAS, lead, arsenic, and more. The UV purifier kills 99% of bacteria and viruses, and a remineralization filter adds beneficial minerals, such as calcium, magnesium, and potassium.

This comprehensive filtration means that no matter what cocktail of contaminants your city water is concealing, your drinking water will be free of it. If contaminant-free water sounds good to you, the Waterdrop G3P800 is what you need. 

Pro 2/5: Efficient, high-capacity filtration

The second major benefit of the G3P800 is its astounding filtration capacity of up to 800 gallons of water per day (depending on your water quality), which also equates to an excellent flow rate. Its 3:1 pure-to-waste ratio means that for every three gallons of purified water produced, only one gallon is wasted. For comparison, the reverse osmosis (RO) industry standard is 1:1 or 2:1, which the G3P800 improves on. 

This system reduces the amount of water sent to the drain, resulting in substantial water and cost savings over time. This same design also ensures a continuous flow of purified water. In contrast, most traditional RO systems store water in a storage tank that, if emptied, takes time to fill up. With the G3P800, you can fill an 8 oz glass in just six seconds, all day long. The other downside to tanks is the increased chance of bacterial contamination, but you won’t have to worry about that with this system. As you can see, the G3P800 has taken traditional RO and made it even better.

While the average American household consumes 300 gallons per day (gpd), the Waterdrop G3P800 provides enough purified water to meet even higher demands, whether you have a large family, entertain guests frequently, or even run a home brewery. If you use a lot of water every day and you want to see less of it wasted, check out the Waterdrop G3P800.

Pro 3/5: Compact design and straightforward installation

The third key feature of the Waterdrop G3P800 is its compact and space-saving design that occupies approximately 70% less space than most under-sink RO systems.

The system is only 5.65 inches wide, meaning you can install it under the sink with plenty of space to spare. As a result, installation is easy and can be completed in under an hour. Waterdrop provides a thorough installation kit, including all essential components, ensuring a straightforward DIY setup. Additionally, Waterdrop provides a helpful YouTube video guide that will walk you through the installation if you run into trouble. 

Traditional, tank-based RO systems take up a lot of space and have a more complex installation. But with Waterdrop’s G3P800, setup is easy and you’ll forget it’s even there.

Pro 4/5: Easy, affordable maintenance

The fourth thing I want to mention about the G3P800 is how easy it is to maintain. It tells you when the filters need replacing, they don’t cost an arm and a leg, and their quick-twist mechanism allows you to remove old filters and replace them with new ones within seconds. 

Just before it’s time to swap out the filters, the built-in filter life indicators remind you in advance so you have time to order more before your water quality is threatened. The cost of the replacements is well below average, and Waterdrop even offers several combos that further reduce the cost. The filter cartridges themselves last a pretty long time (six months on sediment and up to two years for the RO, respectively), so you won’t be ordering and replacing them at every turn. When you do replace them, it takes three seconds to install the filter cartridge — that’s right, three seconds. 

You don’t just want an efficient filtration system; you want a low-maintenance filtration system that you won’t have to coax and coddle on a weekly basis. That’s the Waterdrop G3P800 tankless reverse osmosis system. 

Pro 5/5: Smart faucet with LED screen 

The fifth and final outstanding feature of the Waterdrop G3P800 is its sleek-looking smart faucet and LED screen with real-time water-quality monitoring. This feature takes basic under-sink water filtration and upgrades it with 21st-century style — just what I like to see.

The smart faucet provides valuable information about water quality and filter status. The TDS (total dissolved solids: all the organic and inorganic content dissolved in your water) indicator lets you monitor how well your filter is working. The faucet itself is waterproof, made from lead-free 304 stainless steel, which resists rust, corrosion, and tarnishing. 

By offering real-time monitoring capabilities, this digital display takes the guesswork out of water filtration and puts you in control. If you like modern features, you’ll love the Waterdrop G3P800.

CONS

The Waterdrop G3P800 is a versatile system that’s definitely worth investing in. However, you need to consider these three factors before making a purchase:

Con 1/3: Higher price compared to other under-sink water filters

First, the Waterdrop G3P800 doesn’t provide all those great features without a cost. In fact, it comes with a considerably higher up-front cost than our best budget option. 

The G3P800’s higher price comes down to the system’s advanced features, including its exceptional filtration capabilities and capacity, integrated UV purifier, remineralization filter, and smart faucet. Spending less might mean compromising on what you’re looking for in a filter. Luckily, the G3P800 helps you save in other ways, namely by cutting down on water use and providing long lasting filters that don’t cost a fortune to replace.

Despite the higher up-front cost, the performance, efficiency, and convenience of the Waterdrop G3P800 system make it a worthwhile investment.

Con 2/3: Not suited for well water treatment without pre-filtration

The second downside to this system is its suitability for well water — or lack thereof. Waterdrop is very adamant that the G3P800 not be used to treat well water without pre-filtration due to the risk of damage to the system and reduced effectiveness in removing contaminants. In fact, this characteristic is not unique to the G3P800. Many filtration systems, including the Clearly Filtered below, are best suited to municipal water and require additional considerations for use with well water.

Well water often contains particles such as sediment, iron, manganese, and other impurities that can clog delicate RO membranes. Without pre-filtration to remove these larger particles, the system may experience reduced efficiency and performance over time. 

Because this applies to more than one filter on this list, we’ve included a section below about how to pretreat your well water.

However, if pretreatment sounds counterintuitive to you, and you’re on a well, you give our article a read on the best under-sink water filters for well water.

Con 3/3: Unimpressive warranty

The third con I want to mention is the warranty. The standard warranty for the G3P800 typically covers only manufacturing defects or malfunctions for a period of one year. This is pretty disappointing considering its high purchase price. 

With this warranty, if the system experiences any issues due to defects in materials or workmanship within the first year of ownership, Waterdrop will repair or replace the unit at no additional cost to the user. If it has issues on the 366th day, you’re out of luck. You do get a 30-day money-back guarantee, which helps you try out the system for one month and return it for a full refund if you’re unsatisfied with its performance, but even that is shorter than some of the leading guarantees from other brands.

If you prioritize a long, comprehensive warranty package, the Clearly Filtered system below, which has a lifetime warranty, might be more your speed.

OVERALL: 9.3/10

The Waterdrop G3P800 tankless RO system is the best under-sink water filter overall due to its exceptional filtration capabilities, high capacity, efficient water usage, compact design, and modern features.

While the short warranty might be a drawback for some users, the G3P800’s reliable performance and comprehensive filtration balance out this concern. 

To take advantage of the best in under-sink filtration, order the Waterdrop G3P800 today.

Best Budget: SimPure T1-400 ALK 9.0/10

The SimPure T1-400 tankless reverse osmosis system is the best budget under-sink water filter because of its highly effective multi-stage filtration process, including UV sterilization and remineralization, offering exceptional water purification at an affordable price.

PROS

Four major benefits prove why the SimPure T1-400 Tankless Reverse Osmosis System is the best budget under-sink water filter.

Pro 1/4: Comprehensive multistage filtration

First off, the SimPure T1-400 is the best budget-friendly under-sink system because the low price point doesn’t compromise water quality. The SimPure T1-400 effectively delivers clean, safe, and great-tasting water for everyday use.

This process begins with a sediment filter that removes large particles like sand and dirt, followed by granular activated carbon and carbon block filters to eliminate chlorine, odor, and chemicals. The RO membrane then targets over 1,000 contaminants, including mercury, lead, and arsenic, while a post-carbon filter catches anything that manages to sneak through. The UV sterilizer kills 99% of microbes, then the alkaline filter helps balance pH levels and reintroduces beneficial minerals.

This means you can have clean, safe water without breaking the bank. To protect your family and your bottom line, get the SimPure T1-400 today.

Pro 2/4: Low-key capacity perfect for small homes

The second thing to love about the T1-400 is that you won’t be paying for power you don’t need. It has a gallon-per-day capacity of 400, or 0.28 gallons per minute, which is more than adequate for most families.

Unlike the Waterdrop G3P800, whose 800 gpd capacity is tailored for the biggest households, the T1-400 is more at home in small homes with average to lower-than-average water consumption. You don’t need to worry that this means the T1-400 isn’t going to cut it. Again, the average household only uses 300 gallons per day and the T1-400 can accommodate 400 gpd. 

These days everything is about the biggest and the best, but if you’re looking at the best budget option, you want the best for you, not for everyone. If you’re a single person or new couple just starting out, the SimPure T1-400 will meet your needs and then some.

Pro 3/4: Built-in water pressure gauge

The third outstanding feature of the SimPure T1-400 tankless reverse osmosis system is its built-in water pressure gauge, a unique feature among under-sink water filters.

When water filters are ready for replacement, the buildup of contaminants reduces the water pressure flowing through the filter. By monitoring and displaying the water pressure, this gauge tells you when it’s time to replace the filters. A bonus benefit to this water pressure gauge is that if you know filters are nowhere near needing replacing, fluctuating water pressure in your filter system can alert you to issues within your water line. That’s something a simple LED light measuring the passage of time cannot do.

If you like the idea of a water pressure gauge telling you when your filters need replacing and helping you stay on top of your whole water system, order the SimPure RO system today.

Pro 4/4: Budget-friendly price point

The fourth feature consumers love about the SimPure T1-400 RO system is its affordability. Compared to other water filtration systems, which often come with higher up-front costs due to complex installation and additional components, the SimPure T1-400 offers protection against a wide range of contaminants while still maintaining a budget-friendly price. 

The entire system costs less than $400, including a set of replacements. Even the replacement filters are reasonably priced, ranging from $17 to $50, when you eventually need them. Some reverse osmosis replacements, like for a whole-house system, cost hundreds of dollars annually. SimPure’s replacement costs are totally manageable.

The budget-friendly initial purchase price and low-cost replacement filters mean the SimPure under-sink water filter is a leading option for budget-conscious consumers looking for a financially sustainable and effective water filtration solution.

CONS

While the SimPure T1-400 is a reliable under-sink water filter, it has three downsides:

Con 1/3: Filtration capacity

First, the SimPure T1-400 tankless RO system offers a filtration capacity of 400 gpd, which falls short of the Waterdrop G3P800’s 800 gpd.

This difference in filtration capacity results from the size and efficiency of the RO membrane, the pressure exerted on the water during the filtration process, and the overall design of the system. The lower filtration capacity of the SimPure makes it most suitable for smaller households with lower water usage needs.

It’s important to choose a water filtration system based on household water needs. If you need a system that can filter far more water than you’ll probably ever need, you’ll want the Waterdrop G3P800, but if you’re okay with a system that can easily meet the needs of small families, the SimPure’s 400 gpd capacity is unlikely to limit you. 

Con 2/3: Short warranty

Second, just like the Waterdrop G3P800, the SimPure comes with a relatively short one-year warranty period. 

This warranty covers the system against manufacturing defects and malfunctions for the specified duration. While it also comes with a 30-day money-back guarantee, this short warranty period could potentially leave some users feeling vulnerable, particularly if they encounter any issues or defects with the product after the initial period has expired.

Although the warranty may not offer the same level of protection and peace of mind as longer-term warranties provided by some competitors, the system’s overall performance, effectiveness, and affordability still make it a worthwhile investment for many households.

Con 3/3: Waste ratio could be much better

Finally, while offering efficient filtration, the SimPure T1-400 tankless reverse osmosis system wastes twice as much water as the Waterdrop G3P800. 

This system has a 1.5:1 pure-to-drain ratio, meaning it generates one gallon of wastewater for every 1.5 gallons of purified water it produces. The Waterdrop G3P800 series has a 3:1 low pure to drain ratio. That’s not easy on the environment or your pocketbook. 

If water conservation and eco-friendliness are your top priorities, the Waterdrop G3P800 is the more sustainable choice.

OVERALL: 9.0/10

The SimPure T1-400 is the best budget under-sink water filter due to its low up-front price and excellent filtration, making clean and safe drinking water accessible to smaller households on a budget.

While you may end up spending more on wasted water than you would with a system equipped with a better waste ratio, the system’s comprehensive filtration includes UV sterilization and remineralization, which will even things out if those are two features you’re looking for in an under-sink water filter.

If you’re on your own or a new couple just starting out, you need an under-sink water filter that’s affordable and removes 99% of contaminants without being more powerful than you need. Take action today and invest in the SimPure T1-400.

Best Warranty: Clearly Filtered Water Filter System 8.8/10

The Clearly Filtered 3-Stage Under the Sink Water Filter System is one of the best under-sink water filters because it comes with a lifetime warranty, takes up very little space under the sink, and won’t mean drilling a hole in your kitchen counter.

PROS

Here are four reasons why the Clearly Filtered Under the Sink Filter is worth your consideration:

Pro 1/4: Effective filtration of the most-common contaminants

The first benefit of this filter is its effective filtration. The Clearly Filtered under-sink water filter system boasts a comprehensive three-stage filtration process that filters out many of the most common contaminants.

The system uses a carbon filter to eliminate sediment and particles from the water, also enhancing its taste and odor. It also removes 99.34% of lead, arsenic, chlorine, and volatile organic chemicals (VOCs). In addition to a carbon filter, a proprietary Affinity Filtration Technology removes 90.65% of fluoride.

This means users can enjoy cleaner, safer, and better-tasting water straight from their tap, free from a range of harmful contaminants, with the Clearly Filtered Under the Sink Water Filter System.

Pro 2/4: Compact design

The second major pro of the Clearly Filtered under-sink system is its compact and space-saving design. In fact, it’s the smallest of the top three filters on this list, making it an ideal choice for people with limited under-sink space.

With a sleek and streamlined design, the Clearly Filtered system measures only about three inches in width. Despite its small footprint, the system packs a powerful filtration capability, thanks to its innovative design and advanced filtration technology. 

This means that if you’ve got limited space under your sink and you’re looking for the smallest under-sink water filter out there, you’ll be happy with the Clearly Filtered.

Pro 3/4: Rental-friendly installation and easy maintenance

The Clearly Filtered’s third pro is its straightforward and user-friendly installation and maintenance. Not only is the Clearly Filtered 3-Stage Under the Sink Water Filter System the smallest of my top three filters, but it’s also the easiest to install.

Instead of providing filtered water through a dedicated faucet you have to drill a hole for, the Clearly Filtered system connects to your existing faucet. Users can easily connect the system to the existing cold-water line without the need for permanent modifications, making it a great under-sink system for renters. The system’s modular design also allows for easy filter replacement. Simply twist off the old filters and twist on the new ones without any tools, or even turning off the water supply. Additionally, the filters have a generous filtration capacity of about 2,000 gallons, or 12 months, so you won’t be ordering and replacing them constantly.

If you’re a renter and drilling a hole into your sink isn’t an option, the Clearly Filtered Under the Sink Water Filter System will provide you with clean, safe water and keep your landlord happy too.

Pro 4/4: Lifetime warranty and 30-day money-back guarantee

The final advantage of this filter is that while both the Waterdrop G3P800 and the SimPure T1-400 come with just a year of warranty coverage, the Clearly Filtered system offers coverage for the entire life of the product.

This extensive lifetime warranty reflects the manufacturer’s confidence in the durability and performance of its under-sink water filtration system, assuring you that your investment is safeguarded against any unforeseen issues or malfunctions. Additionally, the system offers a 30-day money-back guarantee, so you can try the product risk-free and return it within 30 days if you are not fully satisfied with your purchase.

What this warranty means is that once you buy this under-sink filter, you’ve got clean water for life. Try the Clearly Filtered system worry-free for 30 days. 

CONS

Like any other system on the market, the Clearly Filtered 3-Stage Under Sink Water Filter System has its fair share of cons, including these three:

Con 1/3: Expensive replacements

First, the replacement filters for the Clearly Filtered system are relatively expensive, costing around $440 for a set of three filters.

Given that the filters have a capacity of 2,000 gallons (or 12 months), this equates to each gallon of water from the Clearly Filtered system costing $0.22. To save money on filter replacements, customers can sign up for the manufacturer’s autoship subscription, which brings the up-front price and replacement filter price down. Keep in mind that these prices are not static and may change.

Despite the discounted rate, these filters are still more expensive than the Waterdrop G3P800 and the SimPure T1-400 replacement filters.

Con 2/3: Limited contaminant removal

Second, the Clearly Filtered 3-Stage system, while effective in removing contaminants, may exhibit comparatively lower contaminant removal rates compared with the Waterdrop and SimPure under-sink water filter systems. 

Unlike those two, the Clearly Filtered system is not an RO system. Reverse osmosis is a highly effective process that removes thousands of contaminants from water. In contrast, this system is meant for the basic filtration of city water and cannot handle radioactive elements (such as radium, uranium, or radon), reduce TDS, or eliminate all VOCs present in water. Furthermore, the system uses proprietary technology, and Clearly Filtered does not disclose the type of filtration behind this special medium. Sure, the first stage is activated carbon, but I couldn’t tell you what the second and third stages are. It says it’s “ionic” but that could mean a lot of things. It claims to have been tested and verified by EPA-accredited laboratories against NSF standards, but it never says which of those standards it’s certified for. We’ve reached out to Clearly Filtered for more information, and I’ll be sure to update this review when we know more. 

It’s important to test your water supply to find the best system to match the contaminants in your tap water, but if you don’t even know what the filtration technology is, it’s harder to match. So, while the Clearly Filtered under-sink filter is a good system that will remove common contaminants, it’s not as good as one that removes more, with full transparency about its limitations.

Con 3/3: No UV filter included 

The final downside of the Clearly Filtered system is its lack of a UV sterilizer, which both the Waterdrop and the SimPure come with. While the Clearly Filtered system offers comprehensive filtration for a wide range of contaminants, it won’t do anything about microbes — bacteria, viruses, and other pathogens.

UV sterilization is highly effective at eliminating a wide range of microbes that can cause waterborne illness. However, it’s important to note that if you’re on municipal water, microbes are not a concern. Your local water treatment plant kills microbes using a combination of chlorination and industrial-strength ultraviolet purification. 

If you like the idea of UV purification anyway, you may be better off with the Waterdrop or SimPure systems. 

OVERALL: 8.8/10

The Clearly Filtered Under the Sink Water Filter System is the best under-sink water filter for consumers who prioritize a robust warranty and don’t want to drill into their counter or sink.

If you need comprehensive contaminant removal, you might be better off with reverse osmosis systems like the Waterdrop G3P800 and SimPure T1-400, which remove over 1,000 contaminants.

However, if you need only selective contaminant removal as well as an enviable warranty and a filter suitable for renters, the Clearly Filtered 3-Stage Under Sink Water Filter is the best choice.

Honorable Mentions

The following three systems did not make it into the top three on our list, but they’re still worth considering:

Express Water Reverse Osmosis System

While not as advanced as some of the top-rated under-sink water filters like the Waterdrop G3P800 or SimPure T1-400, the Express Water under-sink reverse osmosis system is a good choice for people looking for effective filtration at a low, low price. It removes sediment, chlorine, chemicals, heavy metals, and other contaminants, ensuring that the resulting water is clean, clear, and safe for consumption. The system also features a leak detector that shuts off water flow to the filter when it detects unwelcome moisture.

However, the Express Water RO5DX did not make it to the top spots on our list because of a few limitations. One main drawback is its filtration capacity, which is only 50 gallons per day. Additionally, it’s a tank-based RO system, so it will take up a lot of space under the sink, require refilling after heavy use, and come with a more complex installation process than a tankless system would.

Despite not being the top choice, we still chose to include the Express Water RO system as an honorable mention on our list due to its extreme affordability (it’s a few hundred dollars cheaper than our best budget option!) and overall effectiveness. You can find out more about the Express Water under-sink reverse osmosis system here. 

Aquasana Claryum AQ-5300

The Aquasana Claryum AQ-5300 combines activated carbon, catalytic carbon, ion-exchange, and sub-micron filtration to effectively remove a wide range of contaminants, including lead, chlorine, chloramine, mercury, pesticides, pharmaceuticals, and more, while preserving essential minerals like calcium, potassium, and magnesium. It’s a good choice for anyone who wants a tankless under-sink system but doesn’t have a big budget.

While the Aquasana Claryum AQ-5300 offers effective filtration and is easy to use and install, it doesn’t have the same level of advanced features or customization options as our top under-sink water filtration systems. For instance, it doesn’t offer adequate protection against total dissolved solids or microbial contaminants. Because of these limitations, the Aquasana may be unsuitable for untreated well water. 

Check out the Aquasana Under Sink Water Filter if you’re on city water and you’re not worried about total dissolved solids.

The Home Master Artesian Reverse Osmosis System

The Home Master Artesian Reverse Osmosis System is a good choice for homeowners who prioritize exceptional water quality and taste. It’s an RO system, so you know the filtration quality will be excellent. 

At the heart of this RO system is its patented Full Contact Remineralization (FCR) technology, which addresses one of the main drawbacks of traditional RO systems by reintroducing beneficial minerals, such as calcium and magnesium, into the purified water. However, this system has a 1:1 pure-to-waste water ratio, which is just not in line with modern values and capabilities. Additionally, a lot of necessary components, like antimicrobial tubing, cost extra. 

While these drawbacks may impact the decision for some users, the Home Master Artesian RO System still offers good water filtration and a reasonable price tag.

The Bottom Line: Best Under-Sink Water Filter for Your Home

We reviewed dozens of under-sink filters, and it’s clear that the Waterdrop G3P800 is the best under-sink water filter among the different available systems. 

Its thorough filtration, which includes multistage RO filtration, UV sterilization, and remineralization filters, ensures the removal of contaminants while retaining beneficial minerals, providing the highest-quality drinking water. Additionally, its efficient design and high filtration capacity make it a convenient and eco-friendly option for households of all sizes.

If you’re looking for something less costly, the SimPure T1-400 also offers UV filtration and remineralization but at a budget-friendly price point. And for those prioritizing warranty coverage, the Clearly Filtered 3-stage Under the Sink Water Filter has one of the best warranties in the industry.

We invite you to share your thoughts and questions in the comments section below for further assistance. Your feedback will be invaluable to us as we continue to help you make informed decisions about your water filtration needs.

Research Methodology: How We Test and Review Products

To conduct our research and provide an unbiased review of the best filtration products, we apply Drinking Water’s comprehensive water filter product testing methodology. This method helps us systematically sift through the numerous available products, enabling us to identify those truly worth your investment. Here is a summary of the various factors we considered throughout our research:

Use analysis

Once we have a big list of water filters, we begin by delving into the specific use case of each filter. This crucial step enables us to confirm a product fulfills its intended purpose and effectively meets the user’s requirements. Our team of experts carefully verifies whether the filter aligns perfectly with its intended use to ensure it passes this evaluation stage.

You can learn more about our use analysis here. 

Tech check

In this step, we verify whether the filtration technology employed in the filter effectively targets and eliminates the contaminants users want to remove. We conduct extensive assessments to ensure the chosen technology genuinely works. This identifies deceptive practices companies use for marketing.

Learn more about the tech check here.

Water test data

We’ve encountered instances where filter manufacturers have employed incorrect or fabricated test data as a marketing ploy to boost sales. Rather than simply take their word for it, we verify these claims. This thorough validation process ensures users receive filtration systems that provide genuine value for their investment.

Learn more about how we verify water test data. 

Installation test

Installation is crucial when choosing a water filter. Complex setups can cause frustration and unexpected costs, even affecting the product’s fit. We thoroughly assess installation processes to ensure our reviews offer insights that help buyers make informed decisions and avoid potential challenges.

Learn more about our installation test here.

Cost-of-ownership analysis

As homeowners ourselves, we recognize the importance of considering both initial and ongoing costs before investing in a system. This step involves thorough calculations to ensure full awareness of the expenses associated with the filter. We aim to clarify the expenditures involved in every filtration system.

Learn more about our cost-of-ownership analysis. 

Warranty check

We check how strong water filters are and look at warranties as a sign of how good the product is and how reliable the company is. We carefully look at all the details in the warranty to be clear about what they promise. This way, we suggest products from companies that really back up what they sell and care about making customers happy.

Learn more about how we do our warranty checks.

Customer service test

Before suggesting any water filter, we check how good a company’s customer service is. We do tests and checks on their support services to make sure they help customers well after they buy something. This is super important, especially for big buys like whole-house water filters.

Learn more about customer service tests here.

Before You Buy an Under-Sink Filter for Your Home

The key to picking the right filter is matching the technology it uses with the junk that might be in your water. 

The best way to learn what type of filter you need is by sending your water to an accredited laboratory. And this shouldn’t be a once-in-a-lifetime thing. You should test it every few years, annually if you have a private well.

As Jess Goddard — our trusted partner and a water quality engineer — says, “Testing at least once every three years is suggested for utility water users. Water quality is dynamic and changes with engineering practices, regulations, and water sources impacted by a changing climate.” 

What you need to know about pretreatment

Above, I mentioned that many of these filters are not suitable for well water without pretreatment. This is because some impurities that are unique to well water can damage the delicate components of reverse osmosis membranes.

Untreated well water may contain various contaminants, such as bacteria, viruses, and particulate matter (especially iron and manganese), which can cause the following issues if introduced to an RO system without adequate pre-treatment:

Membrane fouling: Excessive levels of iron and manganese in well water can accumulate on the surface of the RO membrane, causing a decrease in water flow and increase in energy consumption. Over time, this can lead to premature failure of the membrane.

Reduced effectiveness: Bacteria and viruses passing through the RO membrane can compromise the safety of the treated well water. If your water is contaminated with microbes, it’s essential that you find out why and make the necessary repairs as well as installing the appropriate filter.

Increased risk of cross-contamination: Backflow of untreated well water into the distribution system can occur if the RO system fails, posing health risks to users.

Several pre-filtration options can protect your RO system and ensure optimal performance, including sediment filters, air-injection oxidation, water softeners (to a lesser degree), and whole-house filters. We’ve written reviews on some of these topics, so check them out:

• Best Sediment Filters for Well Water
• Best Whole-House Filters for Well Water
• Best Water Softeners

Combining multiple systems not only prevents damage, it also sets you up for an even more comprehensive filtration, protecting not only your drinking water, but your home and appliances as well.

Whole-house filters vs. under-sink filters

When searching for a water filter system, the first thing to consider is whether you want water filtered throughout the whole house or just at one source. You’ve got to consult your water reports, as well as your water usage, and decide how much you’re willing to spend sorting it out. 

Each system has its advantages. You need a solution specific to your family’s needs and your water quality.

A whole-house filter treats water from every faucet. It’s set up where the water supply enters your home and protects your pipes, appliances, and plumbing fixtures from corrosion and staining, as well as making your water safe to drink. 

Check out the best whole-house water filters in our thorough review.

A system like this might seem an obvious solution for its thoroughness, but that’s not always the case. For certain homeowners, a whole-house filter might be unnecessary or fall outside their budget. They can cost between $500 and $10,000.

Turning to a point-of-use filter, like an under-sink filter, is a practical and effective solution. Under-sink filters are perfect for targeted filtration to enhance the quality of your drinking water, ensuring it’s fresh, clean, and safe for drinking and cooking. These filters tend to be more affordable in terms of both initial costs and ongoing maintenance. You’ll typically find them within the range of $100–$1,500. Plus, you can easily handle the upkeep yourself in most cases. Their compact designs allow them to fit snugly in tight spaces, and some are even portable, eliminating the need to drill holes in your countertops.

But these won’t protect your plumbing system or water-based appliances from damage due to dirty water, and you won’t be able to access clean drinking water in other areas of the home. 

Sometimes, it’s beneficial to use both a whole-house filter and an under-sink filter, particularly if your water contains multiple types of contaminants. This combination is often ideal for private well owners dealing with sediment, iron, hydrogen sulfide, and hard water. 

A whole-house filter and softener combo effectively deals with sediment, rust, and hard water minerals, while an under-sink water filter focuses on making the softened, sodium-treated water taste and smell fresh and clean.

See our list of the best whole-house filter and water softener combos.

Filtration technology

Under-sink filters come with many designs and technologies. First, identify your contaminants and look for the technology that can remove them. 

Reverse osmosis

Reverse osmosis uses a semipermeable membrane with pores as small as 0.0001 microns, effectively removing up to 98% of total dissolved solids in water. Anything larger than 0.0001 microns gets trapped, encompassing chlorine molecules, organic pollutants, fluoride, salt, VOCs, lead, nitrates, arsenic, and other inorganics. 

It’s important to note that while reverse osmosis filters are adept at capturing numerous contaminants, they’re not a reliable method for eliminating bacteria, viruses, and other microbes in your water.

While RO systems are super effective at treating almost all pollutants in water, they waste a significant amount of water. An average RO filter will produce one liter of clean water out of about three liters of incoming water. This means that just 25%–30% of clean water is generated while 70%–75% is wasted in the process. The best reverse osmosis systems will try to minimize water waste.

Carbon filters

Carbon filters are extremely common and used in all kinds of filters, from multistage whole-house systems to filter pitchers, and everything in between. They typically come in one of two forms:

• Granular activated carbon 
• Carbon block

These filters can capture sediment, chlorine, certain heavy metals, VOCs, trihalomethanes, and other pollutants, including foul tastes and odors.

KDF filters

KDF (kinetic degradation fluxion) uses basic redox reactions to capture contaminants like chlorine, iron, hydrogen sulfide, and lead.

However, KDF does not remove VOCs, pharmaceuticals, pesticides and herbicides, organic cysts, nitrates, fluoride, arsenic, or microbes, so it’s often used as part of a multistage system.

UV filters

UV filters are essential for eliminating microbial contamination from your water supply. These filters utilize 254 nm UV radiation to disrupt the structure of microorganisms, rendering them harmless.

Check out the best UV purifiers. 

Back to product recommendations

Dive Deeper: In-Depth Water Filter Guides

If you’re beginning your journey into water filtration, I’ve gathered a selection of resources that might be beneficial. Here are a few of my top recommendations:

• Best Whole-House Filter for Well Water 
• 7 Best Whole-House Arsenic Filters
• 6 Best Whole-House Iron Filters for Well Water
• 6 Best Whole-House Filters for Lead Removal
• 7 Best Whole-House Carbon Filters
• Best Tankless Reverse Osmosis System
• 9 Best Sediment Filters for Well Water
• How to Clean a Water Filter
• 9 Best Countertop Water Filters
• Everything You Need to Know About Treating Well Water
• The Best Fluoride Water Filters
• The Best Sulfur Filters For Well Water

Frequently Asked Questions

Which under-sink water purifier is best?

The Waterdrop G3P800 tankless reverse osmosis system is the best because of its comprehensive filtration with a high capacity and respectable waste ratio as well as its LED smart faucet that displays your water quality and replacement needs.

Do under-sink water filters actually work?

Yes, under-sink filters effectively remove unwanted pollutants and toxins from your water supply, providing fresh and clean water for drinking and cooking. 

These systems use a combination of filtration technologies to effectively tackle all the contaminants in city and well water. Under-sink filters are a valuable investment for those seeking to enhance their water quality and the point of use.

How do I choose a water filter for under my sink?

Identify the types of contaminants in your water supply and select a filter equipped with the technology to effectively remove them. Measure the space under your sink to find a system that fits easily. Take into account your budget and the size of your family. Consider your preferences for maintenance and installation.

Which water filter removes the most contaminants?

A system that combines reverse osmosis with carbon and sediment filters will remove most of the contaminants in your water. Such an RO system removes chlorine and its by-products, as well as lead, fluoride, arsenic, nitrates, sulfates, organic compounds, and inorganic pollutants.