The Best Under-Sink Water Filter Review

After 30 hours of reporting and research, we believe the Filtrete Maximum Under Sink Water Filtration System With Dedicated Faucet is the best under-sink water filter for most people. Of the hundreds of filters we compared, few can remove as many contaminants, and the Filtrete is easily the most affordable of its kind.

For this guide, which didn’t involve testing, we looked at the most common type of under-sink filter: the kind that uses activated charcoal as the main decontaminant. Hundreds are available, but our pick, the Filtrete Maximum Under Sink Water Filtration System With Dedicated Faucet, is one of the few that meets three strict NSF standards for a wide range of pollutants, including lead and some pharmaceuticals. Most filters that meet these qualifications cost hundreds or even thousands of dollars, but the complete Filtrete system, including a faucet, currently costs about $50. It’s also easy to install and affordable to maintain, with replacement filters that currently cost about $20 apiece, last six months, and can handle 750 gallons—easily enough to satisfy a thirsty family of four for half the year.

Why you should trust me

The basic technology is the same, and so are the NSF standards and tests they’re held to. This said, I had to do a complete crash course on the under-sink category: Unlike the quite limited number of pitcher filters, there are hundreds if not thousands of under-sink filters, each with strengths and weaknesses. In the end, separating the mediocre from the great required a multipronged approach: First, I used NSF’s handy search engine to find a group of candidates that met our criteria for pollution removal; then I searched user and expert reviews to find the ones with the best reputations for functionality and durability; and finally, I reviewed my research at length with a water-quality expert, Steve Richards of Aqua Source Group, who helped me confirm my picks (and steered me clear of a few mistaken assumptions I’d made).I co-authored our guide to pitcher-style water filters, and it turned out much of the research and reporting I did there applies to the under-sink filters I looked at for this guide, too.
Do you need a water filter?

As laid out in detail in our guide to pitcher-style water filters, most Americans’ tap water is perfectly healthy, so in terms of absolute need, the answer is “probably not.”

All US municipal tap water leaves the local water-treatment plant having been tested to stringent federal standards for dozens of potential pollutants and pathogens, from lead and E. coli to a gallery of pesticides. As it flows toward homes and businesses, the water in the mains is also routinely monitored. (New York City conducts almost 1,000 such tests every day—in 2015, no violation of federal standards occurred.)

Simply put, when US tap water goes bad, it’s most often the result of nasty stuff getting into it within the home. Older homes are more vulnerable to problems than new homes, largely due to the use of lead-rich solder (outlawed in 1986) and, in buildings more than a century old, even solid-lead pipes. Utilities take—or should take—steps to lower the probability of lead leaching out of these sources. But they sometimes fail to. That’s what happened in Flint, Michigan: After switching from Detroit’s municipal supply to water from the more-acidic Flint River, the Flint utility failed to add a crucial chemical treatment, orthophosphate, to the water it delivered to customers. Orthophosphate helps “lock in place” the lead present in the pipes of older cities and homes. Without it, the Flint River water began leaching that lead out, resulting in the lead-poisoning crisis. (Chemical & Engineering News has an excellent in-depth article on these events.)

To get a better idea of what, if anything, is in your water, you can request a free “consumer confidence report” from your local utility; it will tell you the exact composition of the water that leaves the treatment plant that serves your address. For ultimate peace of mind, you can also have a local lab test the water that flows from your taps (expect to pay several hundred dollars for the service).
Should you get an under-sink filter?

If you’ve decided you want certifiably “pure” water, you have multiple options. You can get a water service, delivering filtered water in bottles to your fridge or in 5-gallon carboys to a dispenser. You can get a whole-house or—in industry terms—point-of-entry filtration system, but these are mostly aimed at people with exceptionally hard (aka, mineral-rich) water. You can get a pitcher filter (we have tested them and have recommendations), or a countertop unit. You may also be able to install a filter in your fridge’s dispenser. Or you can get an under-sink (“point-of-use”) system.

Pitchers and under-sink filters both work the same way: Water flows through a canister containing activated charcoal and, often, an ion-exchange mechanism made of a specialized resin. The charcoal removes organic compounds, like pesticides, and particulate matter; the ion-exchange resin removes dissolved metals,1 with lead being the one most people are concerned about. (For details on how they work, see our filter-pitcher guide.) The other main class of under-sink filters, reverse osmosis, is not this guide’s focus—here’s why.

Both types are highly effective, but an under-sink system has a few advantages:

Convenience: You can get filtered water instantly just by turning on a faucet, versus having to wait for a pitcher to do its work. That includes saving the time it takes to to open the fridge, fill the pitcher, heave it out of the sink, and put it back in.

Capacity and speed: The highest-capacity under-sink filters can clean 1,000 gallons of water or more; most pitcher filters are rated to just 40 gallons. That means some under-sink filters can go for a year between replacement, whereas a thirsty family of four might need to replace a pitcher filter once a month. (The difference comes down to water pressure. A pitcher filter relies on gravity to draw water through the filter, and that means the charcoal filter has to be composed of loose beads or pellets—otherwise you’d wait all day for a drink. Under-sink filters, by contrast, push relatively high water pressure through a solid block of charcoal, which uses increased surface area and finer perforations to greatly boost the filtration capacity.)

Functionality: Almost anyone can operate a faucet; pitchers can be too heavy and unwieldy for kids and people with arthritis or difficulty with lifting.

Under-sink filters also have some disadvantages:

Size: Under-sink filters take up valuable storage space under the sink. It may not be much—our pick is about the size of a wine bottle, and it’s suspended under the sink, off the cabinet bottom—but it’s a consideration.

Installation: If you’re reasonably handy and have a sink that’s ready to accept an additional faucet—it’ll have an extra hole besides the main faucet, where a soap dispenser (for example) can be put in—you should be able to install an under-sink filter yourself. If not, you’ll probably need to hire a plumber. (Once the filter is plumbed in, you’ll be able to replace filters yourself—most, including our pick, have a simple twist-on-twist-off design.)

Temperature: Water from an under-sink filter is not as cold as water poured from a refrigerated pitcher, or filtered water from a refrigerator’s dispenser. (You’ve got filtered ice, right?)

If, having weighed these factors, you’re still interested in an under-sink filter … read on.
How we picked

By far the most important quality of a water filter is its certified ability to remove unwanted chemicals and pathogens. That word “certified” may seem self-evident, but makers of noncertified filters use convincing language to disguise the fact that their products don’t really do much. So we went right to the industry-standard, independent certifier: NSF International. (You’ve probably seen its logo on some of your cookware—among many other things, NSF certifies kitchen equipment for safety and sanitation.) Manufacturers pay to have NSF test their products, and not every water-filter maker ponies up; when one does, it’s a sign that the manufacturer stands by its product.

Using NSF’s handy, er, filter tool, we pulled up all the under-sink filters that have achieved NSF Standard 53 certification,2 which indicates a filter passed rigorous tests and is known to reduce the levels of a given metallic or organic pollutant to below federally mandated levels.

Makers of noncertified filters use convincing language to disguise the fact that their products don’t really do much.
We also looked at a new NSF category, 401, for “emerging contaminants”—which include pharmaceuticals and estrogen-mimicking compounds. The EPA and others are concerned about the penetration of drugs and estrogen mimics into the water supply, and NSF created Standard 401 in response. Not many carbon-block filters are certified for Standard 401 yet—fewer than 40 at the time of writing—but our pick is one of them.

All the filters we considered are also NSF 42 certified, which means they reduce chlorine and thus improve taste and odor, a simple process and one that NSF classifies as “aesthetic.” (Most water utilities use chlorine to kill germs in the supply.)

Within each standard, filters are certified for specific contaminants. One filter might be certified under NSF 53 to treat only mercury, for example. Another might be certified for several pesticides under NSF 53, but not be certified for mercury. We insisted only on lead and cyst (bacteria) certification, but we favored filters that reduced a wider range of contaminants, including pesticides, industrial chemicals, and drugs.

Filter capacity also narrowed our choices. Most under-sink filters are rated at 100 or 300 gallons, but a few go as high as 1,000 gallons or a bit more. High capacity means fewer filter changes (and less worry about whether it’s time to change the filter—just set an annual or semiannual calendar reminder). So we focused on 500-plus-gallon models, which should meet a family of four’s needs for at least six months. (Note, however, that even if you haven’t gone through a filter’s rated capacity, you should still replace it according to the manufacturer’s recommended timeline. Bacteria can multiply inside filters, if given enough time; replacing the filters on schedule virtually eliminates that possibility.)

We also limited our search to filters that are attached to a separate faucet. Under-sink filters are either mounted “in-line,” meaning the filtered water comes out of the main (existing) tap, or are given their own dedicated tap. We strongly believe the dedicated faucet is a better option than an in-line filter: With a dedicated faucet, you can use filtered water for all your drinking and cooking needs, but you won’t waste the filter’s capacity on jobs that don’t need filtered water, like washing the dishes.3

Flow-rate was another factor. Under-sink filters tend to hover in the 0.5 to 0.75 gallons-per-minute range. That may not seem like much of a difference, but for comparison, the standard faucet in many sinks delivers 2.2 gpm. When filling a drinking glass or pot from the filtered faucet, a 50-percent-faster pour makes a big difference in how long you’re standing there waiting—so we favored 0.75 gpm models.

Upfront cost and the cost of replacement filters were also a concern, and under-sink filters range from less than $50 to nearly $2,000. So we aimed for the best overall value—but only after a filter met the criteria listed above.

Finally, because we wouldn’t be testing the candidate filters ourselves, we delved into user reviews and ratings, discarding any otherwise likely seeming models that got low ratings or frequent complaints about design flaws or difficult installation and maintenance. As always, we turned to reliable reported sources, including Consumer Reports, for further insights. And we spoke at length with Steve Richards of the Aqua Source Group, a water-treatment firm that’s served the Rochester, New York, area for almost 30 years. Richards has achieved many of the highest certifications offered by the Water Quality Association—among others, he’s a Master Water Specialist—and he answered our (many) in-depth questions about NSF standards, the various types of filters available, and the filters we considered for this guide.

One last thing: We’re assuming that you’re connected to a municipal water supply, which—again—are highly regulated and pretreated for contaminants. But if you draw water from a private well or other nonmunicipal source and are concerned about contaminants, you must consult a local water-quality expert for advice.
Our pickOur under-sink water filter pick comes with all the hardware you need, including the faucet—not always the case with others we compared it with.