Jun 10, 2023

The Best Under

We’ve updated the guide to note the Aquasana AQ-5200 now has ANSI/NSF certification for microplastic removal. Our picks remain unchanged.

Anyone who goes through more than a couple of gallons of drinking water a day will probably be happiest with an under-sink filtration system like the Aquasana AQ-5200. If you prefer (or need) filtered water, this provides a continuous supply of it on demand from a separate tap. We recommend the Aquasana AQ-5200 because its certifications are among the best of any system we’ve found.

Certified for the most contaminants, widely available, affordable, and compact, the Aquasana AQ-5200 is the under-sink water filter system we’d look for first.

*At the time of publishing, the price was $153.

The Aquasana AQ-5200 is ANSI/NSF-certified to virtually eliminate a wide array of contaminants, including lead, mercury, volatile organic compounds, pharmaceuticals, and other materials that few of its competitors catch. It's one of a handful of filters certified for PFOA and PFOS, compounds involved in the manufacture of nonstick materials that received an EPA Health Advisory in February 2019. In 2022, it was also certified to remove microplastics, raising its total certifications from 77 to 78.

Replacement filters cost about $60 for a set, or $120 per year on Aquasana's recommended six-month replacement cycle. And, being barely larger than a couple of cans of soda, the system doesn't take up a lot of valuable room under your sink. This widely available system uses high-quality metal hardware, and its faucet comes in multiple finishes.


Identical to the Aquasana AQ-5200 in certifications, specs, and size, the A.O. Smith AO-US-200 is exclusive to Lowe's, so not as widely available.

May be out of stock

*At the time of publishing, the price was $140.

The A.O. Smith AO-US-200 is identical to the Aquasana AQ-5200 in every important respect. (That's because A.O. Smith bought Aquasana in 2016.) It has the same exceptional certifications, all-metal hardware, and compact form, but because it's sold only at Lowe's it's not as widely available, and its faucet comes in only one finish: brushed nickel. If that suits your style, we recommend shopping between the two models by price: one or the other is frequently on sale. Filter-replacement costs are similar: about $60 for a set, or $120 a year on A.O. Smith's recommended six-month cycle.

With the same great certifications but a higher flow rate and filter capacity, the AQ-5300+ works for homes that use a lot of water—but it costs a bit more and takes up more space under the sink.

$175 + FS w/code AQWC50

*At the time of publishing, the price was $196.

The Aquasana AQ-5300+ Max Flow has the same exceptional 77 ANSI/NSF certifications as our other top picks but offers higher flow (0.72 versus 0.5 gallons per minute) and filter capacity (800 versus 500 gallons). That makes it our pick for households that need a lot of filtered water and want it as fast as possible. It adds a sediment prefilter, too, which the AQ-5200 lacks; this may extend the contaminant-filters’ higher flow in homes with sediment-rich water. That said, the AQ-5300+ model—with three liter-bottle-size filters—is much larger than the AQ-5200 and the A.O. Smith AO-US-200 but has the same recommended filter lifespan of six months. And it costs a bit more up front and for replacement filters (about $80 a set or $160 a year). So weigh its benefits against its higher cost.

The Claryum Direct Connect installs without drilling and delivers up to 1.5 gallons of filtered water per minute through your existing faucet.

May be out of stock

*At the time of publishing, the price was $100.

Aquasana's Claryum Direct Connect plumbs right into your existing faucet, making it a particularly attractive choice for renters (who may be forbidden from altering their place) and for people who can't install a separate filter-faucet. It doesn't even have to be mounted on the sink-cabinet wall—it can simply lie on its side. It offers the same 77 ANSI/NSF certifications as our other Aquasana and A. O. Smith picks do, and it can deliver up to 1.5 gallons per minute of filtered water, more than the others. The filter is rated for 784 gallons, or about six months of use. But it lacks a sediment prefilter, so if you have a sediment issue, it's not a good choice, as it can clog. And it's big—20½ by 4½ inches—so if your sink cabinet is small or crowded, it may not fit.

Certified for the most contaminants, widely available, affordable, and compact, the Aquasana AQ-5200 is the under-sink water filter system we’d look for first.

*At the time of publishing, the price was $153.

Identical to the Aquasana AQ-5200 in certifications, specs, and size, the A.O. Smith AO-US-200 is exclusive to Lowe's, so not as widely available.

May be out of stock

*At the time of publishing, the price was $140.

With the same great certifications but a higher flow rate and filter capacity, the AQ-5300+ works for homes that use a lot of water—but it costs a bit more and takes up more space under the sink.

$175 + FS w/code AQWC50

*At the time of publishing, the price was $196.

The Claryum Direct Connect installs without drilling and delivers up to 1.5 gallons of filtered water per minute through your existing faucet.

May be out of stock

*At the time of publishing, the price was $100.

I have been testing water filters for Wirecutter since 2016. In my reporting, I’ve spoken at length with filter-certification organizations to understand how their testing is conducted, and delved deeply into their public databases to confirm that manufacturers’ claims are supported by certified testing. I’ve also spoken with representatives of multiple water-filter manufacturers, including Aquasana/A.O. Smith, Filtrete, Brita, and Pur, to interrogate their claims. And I’ve gone hands-on with all of our picks, because overall livability, durability, and user-friendliness are important in a device you’ll use multiple times a day.John Holecek, a former NOAA scientist, researched and wrote earlier Wirecutter water-filter guides, conducted his own tests, commissioned further independent tests, and taught me much of what I know. My work builds on his.

Unfortunately there's no universal answer to whether you need a water filter. In the United States, public water supplies are regulated by the EPA under the Clean Water Act, and water leaving a public water-treatment plant must meet strict quality standards. But not all potential contaminants are regulated. As well, contaminants can enter the water after it leaves the treatment plant, by infiltrating leaky pipes (PDF) or by leaching out of the pipes themselves. And water treatments done (or overlooked) at the plant can exacerbate leaching in pipes downstream—as happened in Flint, Michigan.

To know exactly what's in your supplier's water when it leaves the plant, you can usually find your local supplier's EPA-mandated Consumer Confidence Report online; if not, all public water suppliers are required to give you their CCR upon request. But because of potential downstream contamination, the only way to know for certain what's in your home's water is to pay a local water-quality lab to test it.

As a rule of thumb: The older your home or community is, the greater the risk of downstream contamination. The EPA says that "homes built before 1986 are more likely to have lead pipes, fixtures and solder"—once-common older materials that don't meet current codes. Age also brings an increased likelihood of legacy groundwater pollution from pre-regulation industry, which can be a risk, especially when combined with age-related degradation of underground plumbing.

If your household goes through more than two or three gallons of drinking water each day, an under-sink water filter may be a better choice than a pitcher filter. Under-sink systems provide filtered drinking water on demand, with no waiting around for the filtration process to run its course, as there is with pitchers. "On demand" filtration also means under-sink systems can provide enough water for cooking—you could fill a pot to cook pasta with filtered water, for example, but you’d never repeatedly refill a pitcher for that.

Under-sink filters also tend to have much more capacity and much longer lifespans than pitcher filters—often hundreds of gallons and six months or more, versus 40 gallons and two months for most pitcher filters. And because under-sink filters use water pressure, not gravity, to push water through the filter, their filters can be denser, so they can remove a greater range of potential contaminants.

On the downside, they’re more expensive up front than pitcher filters, and replacement filters are also more expensive in absolute terms and averaged over time. The system also takes up space in your sink cabinet that could otherwise be used for storage.

Installing an under-sink filter requires basic plumbing and hardware mounting, but the job is straightforward only if your sink already has a hole for a separate faucet. If it doesn't, you’ll need to knock out one of the built-in faucet sites (visible as a raised disk on steel sinks, or a marking on synthetic-stone sinks). Lacking a knockout, you’ll need to drill a hole through the sink, and if your sink is an under-mount, you’ll need to drill through your countertop as well. If you currently have a soap dispenser, an air gap for a dishwasher, or a handheld sprayer on your sink, you could remove that and install the faucet there.

Certified to remove contaminants, these water filters, pitchers, and dispensers can improve home drinking water.

This guide is about a specific type of under-sink filter: those that use cartridge filters and send the filtered water to a separate faucet. These are the most popular under-sink filters. They take up little room and are generally simple to install and maintain. They use adsorbent materials—typically, activated carbon and an ion-exchange resin, just like pitcher filters—to bind and neutralize contaminants. We’re not talking about faucet-mounted filters, reverse-osmosis systems, or other pitchers or dispensers.

To ensure that we recommend only trustworthy filters, we have always insisted that our picks be certified to the industry standard: ANSI/NSF. The American National Standards Institute and NSF International are private, nonprofit organizations that, working in concert with the EPA, industry representatives, and other experts, establish strict quality standards and testing protocols for thousands of products, including water filters. The two main certifying labs for water filters are NSF International itself and the Water Quality Association (WQA). Both are fully accredited in North America by ANSI and the Standards Council of Canada to do ANSI/NSF certification testing and both must adhere to the exact same testing standards and protocols. Filters can meet the certification standard only after being pushed well beyond their expected lifespan, using prepared "challenge" samples that are far more polluted than most tap water.

For this guide we focused on filters with certifications for chlorine, lead, and VOC (aka volatile organic compounds).

Chlorine certification (which falls under ANSI/Standard 42) is important, because chlorine is the usual culprit for "bad-tasting" tap water. But it's also almost a gimme: Virtually all water filters of any type are certified for it.

Lead certification is hard to achieve because it means reducing a lead-rich solution by more than 99 percent.

VOC certification is also challenging, because it means that a filter virtually eliminates more than 50 organic compounds, including many common biocides and industrial precursors. Not all under-sink filters have either certification, so by focusing on filters with certification for both, we identified those with markedly superior performance.

We further narrowed our search by favoring filters that are additionally certified under a relatively new ANSI/NSF standard, 401, which covers emerging contaminants, like pharmaceuticals, that are increasingly found in US water. Again, not all filters have 401 certification, so those that do have it (along with lead and VOC certification) are a very select group.

Within this stringent subset, we then looked for those with a minimum capacity of 500 gallons. That equates to a filter lifespan of roughly six months under heavy use (2¾ gallons a day). That's enough daily filtered water for most families to both drink and cook with. (Manufacturers provide suggested filter-replacement schedules, usually given in months rather than gallons; we abide by these recommendations in our assessments and cost calculations. We recommend always using original-manufacturer replacements, rather than third-party filters.)

Finally, we weighed costs, for both the entire system up front and for the ongoing cost of replacement filters. We did not set a price floor or ceiling, but our research revealed that while up-front costs ranged from the low $100s to $1,250, and filter costs from $60 to almost $300, these differences weren't reflected in markedly superior specs for the more expensive models. We found several under-sink filters that came in at well under $200 while offering exceptional certifications and lifespans. These became our finalists.Beyond this, we looked for:

While researching, we ran into occasional reports of catastrophic leaks from owners of under-sink water filters. Because the filters are plumbed into the cold-water feed line, if a connector or hose breaks, water will escape until the shut-off valve is closed—meaning it could be hours or even days before you discover the problem, leaving you with severe water damage. It's not a common occurrence, but is a risk to weigh when considering buying an under-sink filter. And if you do buy one, follow the installation instructions carefully, take care not to cross-thread the connector, and turn the water back on slowly to check that there are no leaks.

Reverse osmosis, or R/O, filters initially employ the same sort of cartridge filters as our picks here but add a secondary reverse-osmosis filtration mechanism: a fine-pored membrane that lets water through but filters out dissolved minerals and other substances.

We may address R/O filters in depth in a future guide. Here, we categorically dismissed them. They offer limited functional advantages over adsorbent filters; they produce significant amounts of wastewater (typically 4 gallons of wasted "rinse" water per gallon filtered), while adsorbent filters produce none; they take up far more room, because unlike adsorbent filters they employ a 1- or 2-gallon tank to store filtered water; and they are far slower than under-sink adsorbent filters.

We’ve conducted lab tests of water filters in years past, and our main takeaway from testing was that ANSI/NSF certification is a reliable measure of a filter's performance. That's not surprising given the extreme rigor of the certification testing. Since then we have relied on ANSI/NSF certifications, rather than our own limited testing, to select our competitors.

In 2018 we conducted tests on the popular Big Berkey water-filter system, which is not ANSI/NSF certified but claims to have been extensively tested to ANSI/NSF standards. That experience further cemented our insistence on true ANSI/NSF certifications and our distrust of "tested to ANSI/NSF" claims.

Our tests since then, including in 2019, have focused on real-world usability and the kinds of practical features and drawbacks that become apparent when you’re living with these products.

Certified for the most contaminants, widely available, affordable, and compact, the Aquasana AQ-5200 is the under-sink water filter system we’d look for first.

*At the time of publishing, the price was $153.

Our pick is the Aquasana AQ-5200, aka the Aquasana Claryum Dual-Stage. Its most important feature by far is that its filters have the best ANSI/NSF certifications among our contenders, including chlorine, chloramine, lead, mercury, VOC, multiple "emerging contaminants," and PFOA and PFOS. Beyond that, its faucet and plumbing hardware are made of solid metal, which is superior to the plastic that some other manufacturers use. And this system is also extremely compact. Finally, the Aquasana AQ-5200 is one of the best values we’ve found in under-sink filters, typically costing about $140 up front for the whole system (filters, housing, faucet, and hardware) and $60 for a set of two replacement filters. That's less than many competitors with weaker certifications.

The Aquasana AQ-5200 is ANSI/NSF certified (PDF) for 78 contaminants. Its filter uses the same technology as the Aquasana AQ-5300+ and A.O. Smith AO-US-200, but those filters currently lack certification for microplastics. That makes the AQ-5200 the most robustly certified system among our picks. (A.O. Smith bought Aquasana in 2016 and has adopted much of its technology; A.O. Smith has no plans to phase out the Aquasana line.) For comparison, the excellent Pur Plus Filter is certified for 23.

These certifications include chlorine, which is used to kill pathogens in municipal water supplies and is the chief cause of "bad-tasting" tap water; lead, which can leach out of old pipes and pipe solder; mercury; live cryptosporidium and giardia, two potential pathogens; and chloramine, a persistent chlorine-ammonia disinfectant that is increasingly employed by filtration plants in the US South, where pure chlorine rapidly degrades in the warm water. The Aquasana AQ-5200 is also certified for 15 "emerging contaminants" that are increasingly found in public water supplies, including BPA, ibuprofen, and estrone (a form of estrogen used in birth control); and for PFOA and PFOS—fluorine-based compounds used to make nonstick substances, and which received an EPA Health Advisory in February 2019. (At the time of the advisory, only three manufacturers in this category of filters were certified for PFOA/S, making this particularly noteworthy.) It is also certified for VOC. That means it effectively removes more than 50 different organic compounds, including many pesticides and industrial precursors.

Along with activated carbon and an ion-exchange resin, which are common to most if not all under-sink filters, Aquasana uses two additional filter technologies to achieve its certifications. For chloramine, it adds catalytic carbon, a more porous and therefore more reactive form of activated carbon produced by treating the carbon with high-temperature gas. For cryptosporidium and giardia, Aquasana manufactures its filters in such a way that the pore size is reduced to 0.5 micron, which is small enough to physically capture them.

The Aquasana AQ-5200 filter's exceptional certifications are the main reason it's our pick. But its design and materials also set it apart. The faucet is made of solid metal and so is the T-shaped fixture that attaches the filter to the plumbing. Some competitors use plastic for one or both, lowering cost but increasing the risk of cross-threading and mis-installation. The AQ-5200 employs compression fittings to ensure a tight, secure seal between your plumbing and the plastic tubing that sends water to the filters and tap; some competitors use simple push-in fittings, which are less secure. And the AQ-5200 faucet is available in three finishes (brushed nickel, polished chrome, and oiled bronze), whereas some competitors give you no choice.

We also favored the AQ-5200 system's compact form. It uses a pair of filters that are each little bigger than a soda can; some other filters, including the Aquasana AQ-5300+, below, are the size of liter bottles. With the filters installed on the mounting bracket, the AQ-5200 measures 9 inches high by 8 inches wide by 4 inches deep; the Aquasana AQ-5300+ is 13 by 12 by 4 inches. That means the AQ-5200 takes up significantly less room in the sink cabinet, can fit in cramped spaces where larger systems would not, and leaves more room for under-sink storage. You need about 11 inches of vertical space (measuring downward from the top of the housing) to permit filter replacement, and about 9 inches of unobstructed horizontal space along a cabinet wall to install the housing.

The AQ-5200 is very well reviewed for a water filter, with 4.5 stars (out of five) across more than 800 reviews at Aquasana's site, and 4.5 stars across nearly 500 reviews at Home Depot.

Finally, at its current price of about $140 (and often on sale for closer to $100) for the complete system and $60 for a set of replacement filters ($120 per year on a six-month replacement cycle), the Aquasana AQ-5200 is one of the very best values among our competitors, costing hundreds less than some models whose certifications aren't as extensive. The unit contains a timer that begins beeping when you’re due for a filter replacement, but we recommend also setting a recurring calendar reminder on your phone. (You’re less likely to miss it.)

The Aquasana AQ-5200 has a lower maximum flow rate relative to some competitors (0.5 gpm versus 0.72 or more) and lower capacity (500 gallons versus 750 or more). This is the direct result of its physically small filters. On balance, we think these minor drawbacks are outweighed by its compactness. If you know you want higher flow and capacity, the Aquasana AQ-5300+ is rated to 0.72 gpm and 800 gallons but shares the same six-month filter-replacement schedule, and the Aquasana Claryum Direct Connect delivers up to 1.5 gpm and is rated to 784 gallons and six months.

The AQ-5200 system's instruction manual is a bit sloppy, with a few parts not shown on the parts list or diagram. It's nothing that will trip up most owners; fundamentally, all you’re doing is attaching a couple of tubes to the water supply and the faucet, and the parts more or less explain themselves. (The unlisted, decorative stainless washer is the exception: it goes onto the faucet first, before the thin rubber washer.) And in fairness, sloppiness is a problem with many under-sink filters’ manuals, judging by the comments we came across in our research. But we’d like to see the manual rectified in the future. In the meantime, here's a video from Aquasana of how to install the AQ-5200.

As noted above in How We Picked, under-sink water filters, including the AQ-5200, occasionally fail catastrophically, causing severe water damage if the problem is not quickly noticed and fixed. Be particularly careful when installing that you don't cross-thread the connector and that the hose connections are secure, and turn the water back on slowly, so you can catch and rectify any leaks before they become a disaster.

Like all our picks, the Aquasana AQ-5200 comes with its own separate faucet, which may not match your style. You can also install a separate faucet of your choice, as long as the faucet connection is ⅜ inch. But you’ll want to match its flow rate to the Aquasana's 0.5 gpm, because filter certifications are tied to flow. And note that using your own faucet technically means your system is no longer ANSI/NSF certified.

If you suspect your water is sediment-rich (an orange-ish tint, from rust, is one clue; so is past experience with filters of any sort, including pitchers, becoming clogged before their projected lifespan), you may wish to look at the otherwise similar Aquasana AQ-5300, which adds a sediment prefilter.

Identical to the Aquasana AQ-5200 in certifications, specs, and size, the A.O. Smith AO-US-200 is exclusive to Lowe's, so not as widely available.

May be out of stock

*At the time of publishing, the price was $140.

The A.O. Smith AO-US-200, marketed as (prepare for a mouthful) the Clean Water Filter Dual-Stage Carbon Block Under Sink Water Filtration System, is functionally and in every important respect physically identical to the top-pick Aquasana AQ-5200. It has the same 77 ANS/NSF certifications (PDF) and the same compact size, filter technologies, all-metal construction, compression fittings, and 0.5 gpm flow and 500-gallon capacity. It also usually sells for about the same price up front and for a set of replacement filters. None of this is suspicious: A.O. Smith purchased Aquasana in 2016, and as an A.O. Smith representative told us, is "leveraging" Aquasana's expertise while having no plans to phase out the Aquasana brand.

The A.O. Smith filter differs from the Aquasana AQ-5200 in only two respects. First, it's exclusive to Lowe's. Second, its faucet comes in only a brushed-nickel finish, while the AQ-5200 faucet comes in brushed-nickel, polished-chrome, and oiled-bronze versions. If brushed nickel suits your decor, we recommend shopping around. Sales can significantly reduce the price of one relative to the other. As a Lowe's exclusive the A.O. Smith has fewer reviews but the feedback so far is solid.

As for flaws, the A.O. Smith's manual is sloppy in the same ways the Aquasana 5200 manual is. And our A.O. Smith came with a single 6-foot length of plastic tubing; it's supposed to come with two 3-foot lengths, as the AQ-5200 did. The tubing was easy to cut in half (we tested with scissors, kitchen shears, and a wire cutter), but owners shouldn't have to take that step themselves.

With the same great certifications but a higher flow rate and filter capacity, the AQ-5300+ works for homes that use a lot of water—but it costs a bit more and takes up more space under the sink.

$175 + FS w/code AQWC50

*At the time of publishing, the price was $196.

With identical certifications to the Aquasana AQ-5200 and the A.O. Smith AO-US-200 but higher flow rate and larger capacity, the Aquasana 5300+ Max Flow is our pick for people who need a lot of filtered water and want it fast. But it's a physically much larger system (see the comparative photo below) and costs more up front and to replace the three filters.

The Aquasana AQ-5300+ Max Flow is ANSI/NSF certified for the same 77 contaminants (PDF) as the 5200 and A.O. Smith filters, including chlorine, chloramine, lead, mercury, VOC, PFOA, and PFOS. The AQ-5300+ Max Flow adds a prefilter for capturing rust and sediment that may be in the water supply, helping keep the contaminant filters from clogging; the AQ-5200 and A.O. Smith filters lack this feature.

The AQ-5300+ Max Flow uses all-metal hardware that's identical to the Aquasana AQ-5200 and the A.O. Smith filters, and like the AQ-5200, the faucet comes in three finishes: brushed nickel, chrome, and oil-rubbed bronze. And the AQ-5300+ Max Flow has the same secure compression fittings, helping prevent leaks.

The AQ-5300+ Max Flow delivers water more quickly than the AQ-5200 and the A.O. Smith filters: it's rated to 0.72 gpm, versus 0.5. And its filters have a higher capacity, at 800 versus 500 gallons. But that does not extend the filters’ recommended lifespan: they’re rated to the same six months. At about $80 versus $60 for a set of replacements, that translates to about $40 more annually. And the AW-5300+ Max Flow is more expensive up front, at around $150 (though often on sale for less).

The AQ-5300+ Max Flow is well reviewed, with 4.6 stars (out of five) across more than 900 reviews at Home Depot and 4.6 stars across nearly 1,500 reviews at Aquasana's site.

But the AQ-5300+ Max Flow is physically much larger than the AQ-5200 and the A.O. Smith filters, at 13 by 12 by 4 inches versus 9 by 8 by 4 inches. It will take up more room in your under-sink cabinet and may not fit at all if your cabinet is particularly small or cramped. You need about 15 inches of vertical space (measuring downward) from the top of the housing to permit filter replacement, and about 13 inches of unobstructed horizontal cabinet wall to screw the housing into place.

One other note: The AW-5300+ Max Flow is equipped with a "performance indicating device" (PID). That means it measures the actual amount of water that passes through the device, while the AQ-5200 and A.O. Smith filters have simple timers. The PID is Bluetooth enabled, as well, so it can alert your phone or laptop when the filters are due for replacement. We still recommend setting a calendar reminder on your phone, as you’re more likely to see the reminder and don't have to worry about the PID malfunctioning or running out of power.

The Claryum Direct Connect installs without drilling and delivers up to 1.5 gallons of filtered water per minute through your existing faucet.

May be out of stock

*At the time of publishing, the price was $100.

The Aquasana Claryum Direct Connect is an under-sink filter with particular utility for renters and for people in homes that don't have a separate mounting hole for a filter-dedicated faucet. That's because it plumbs directly into the cold-water line and sends filtered water to the main faucet—you don't have to drill any holes or otherwise alter your space. This design also makes the Claryum Direct Connect easier to install than our other picks, which need that separate faucet installed and also require you to mount the filters on the sidewall of the sink cabinet. In contrast, the Claryum Direct Connect can simply lie on the cabinet floor (though it comes with mounting brackets if you prefer to secure it horizontally or vertically).

The Claryum Direct Connect has the same exceptional ANSI/NSF certifications as our other picks from Aquasana and A.O. Smith. (The latter is a Lowe's-exclusive Aquasana brand—the exact A. O. Smith equivalent to the Claryum Direct Connect is the A. O. Smith Clean Water Main Filter.) It reduces lead, mercury, PFOA/PFOS, and some pharmaceuticals, a total of 77 contaminants. The filters are rated for 784 gallons, or about six months’ worth of normal use, and Aquasana claims a flow rate of up to 1.5 gallons per minute—three times faster than that of the top-pick Aquasana AQ-5200 and twice as fast as the flow rate of the AQ-5300+.

In our initial testing, we measured zero change in a home faucet's flow after installing the Claryum Direct Connect: It delivered the same 1.25 gallons per minute that it did before. However, after unrelated plumbing repairs elsewhere in the multi-unit building sent a huge burst of sediment into the pipes, the filter clogged, and the flow dropped to just 0.5 gpm. If you know or suspect that you have sediment issues, Aquasana recommends our upgrade pick, the AQ-5300+, because unlike the Claryum Direct Connect it has a sediment prefilter.

Installing the Claryum Direct Connect is straightforward. You simply shut off the cold-water inlet valve, unscrew the existing coupling to the sink's water line, and screw in the provided adapter. Two sections of tubing, also included, connect the filter to the adapter, using simple press-fit collars. You can leave the filter lying on the floor of the sink cabinet or mount it on the brackets that Aquasana provides. We were able to do the job in about 10 minutes; the only tools you need are an adjustable wrench and, if you opt for the brackets, a screwdriver.

Be aware, however, that the filter is much larger than our other picks at 20½ inches long and 4½ inches wide, and you need 3 inches of additional space below it or next to it to remove a spent filter and put a new one in. So take some measurements before buying.

Because the Claryum Direct Connect is connected to the main faucet, every time you turn on the cold water, you use up a bit of filter life. The filter's high capacity makes that less of a concern than it would otherwise be, but we can imagine people altering their water usage in a bid to maximize the filter's lifespan. ("You’re definitely not pre-rinsing those dishes now," quipped Harry Sawyers, editor of this guide.) Of course, you also get the convenience of instant, free-flowing filtered water and easy installation, and we consider that a fair trade-off. When it's time for a replacement filter, the old one twists out and the new one twists into place, the work of less than a minute.

Reviews of the Aquasana Claryum Direct Connect are generally very positive—with one common source of complaint, and a valid one. The adapter piece is made of plastic, and it's too easy to cross-thread that piece during installation and strip the threads, rendering it useless. If you just take a little care, it shouldn't be an issue, but a brass adapter would be sturdier and less prone to this problem.

The Hahn 3-stage 600-gallon is a re-branded version of the Aquasana AQ-5300. It has the same 77 ANSI/NSF certifications as the Aquasana 5200, 5300, 5300+ Max Flow, and the A.O. Smith AO-US-200. And like the 5300 and 5300+ Max Flow, it has a sediment prefilter. It's not as widely available as any of these, but if you see one at a competitive price and if you know you have high sediment in your pipes, it's a solid choice.

The Amway eSpring 100189 has more ANSI/NSF certifications than any other filter we discovered in our research, including lead, VOC, Standard 401 "emerging contaminants," and PFOA and PFOS. But it costs $1,250. That's almost 10 times what our picks cost, which made it easy to dismiss.

The Aquasana AQ-5300 sits between the top-pick AQ-5200 and upgrade-pick 5300+ Max Flow. It's physically almost identical to the AQ-5200 but adds a sediment prefilter (like the 5300+ Max Flow) to help extend the contaminant filters’ lifespans. If you know your water is rusty or sediment-rich, this filter may be worth the slightly higher up-front and maintenance costs. It has same ANSI/NSF certifications and 0.5 gpm flow as the AQ-5200, a slightly higher 600-gallon capacity, and the same six-month filter replacement schedule but is a bit wider (12 inches versus 8 inches) due to the third filter.

Brondell's popular H2O+ Coral UC300l has lead and VOC certification but no Standard 401 "emerging contaminants" certifications.

The 3M Aqua-Pure AP-DWS1000, an informal recommendation in the previous version of this guide, costs considerably more than our picks and lacks Standard 401 "emerging contaminants" certifications.

The Body Glove BG-12000, also a former informal recommendation, is rated to a relatively high 0.75 gpm and 750 gallons but has fewer certifications than our picks and costs more than $500, and you have to buy a faucet separately. The BG-3000 lacks Standard 401 certifications and is rated to just 450 gallons, and again costs more than our picks and doesn't come with a faucet.

The popular Brita Redi-Twist WFUSS-334 is not a Brita product but licenses Brita's name. It lacks VOC and Standard 401 certifications and costs more than our picks.

The Camelot Imperial Plus is certified for lead and VOC but not Standard 401 "emerging contaminants" and costs $1,800.

APEC's popular WFS-1000 is not certified for any of its claims by NSF or WQA.

No Ecodyne filter in the under-sink, non-reverse-osmosis category met our requirements. (The company primarily focuses on industrial, pool, and spa filtration.)

The iSpring US31 is not certified by NSF or WQA but rather is "independently tested" to their standards.

The Frizzlife MP99, an "Amazon's Choice," also is not certified by NSF or WQA.

No EcoWater filter met our requirements of lead and VOC reduction and 500-gallon capacity.

The GE Single Stage Filtration System does not have NSF or WQA certifications.

The Pentair F2000-B2B has lead and VOC certifications but not Standard 401, and is not widely available.

Shaklee's BestWater MTS2000 Model 82333 is NSF-certified for lead and VOC and rated to 1,000 gallons, but we found very little further information about it.

The WaterChef U9000 is certified for lead and VOC but not Standard 401 "emerging contaminants." That and its high cost mean it's not our pick, despite its 1,000-gallon capacity and 0.75 gpm flow rate.

Tim Heffernan

Tim Heffernan is a senior staff writer at Wirecutter and a former writer-editor for The Atlantic, Esquire, and others. He has anchored our unequaled coverage of air purifiers and water filters since 2015. In 2018, he established Wirecutter's ongoing collaboration with The New York Times's Smarter Living. When he's not here, he's on his bike.

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