Best under sink reverse osmosis water filtration system

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Although water filter pitchers can be effective at filtering contaminants from tap water, they require constant refilling, especially if you're drinking enough water each day. Instead, experts suggest investing in an under-sink water filter, which allows you to get clean water right from the tap.

“Under-sink water filters are a much more convenient option to filter your tap water because they don’t take up counter space, and they even offer better filtration since they use water pressure (as opposed to gravity) to filter out contaminants,” says Gabe Pinchev, founder and CEO of FieldPulse, an online platform for service contractors.

There are several different types and mechanisms to choose from, with different options for filters and installation. “You want to make sure your filters are effective, that you can change them easily, and that your maintenance and operation costs are under control,” explains Paul Lewin, plumbing expert and founder of home maintenance blog Home Water Research.

Our pick for the best overall under-sink water filter is the Aquasana Claryum 3-Stage Max Flow because of its multi-filtration technology and fast water flow.

Keep reading for our recommendations for the best under-sink water filters.

Who it’s for: People who want a filter with a fast water flow. 

Who it isn’t for:

For effectively and quickly filtering large amounts of tap water, the Aquasana Claryum 3-Stage Max Flow can’t be beat. This water filter is NSF-certified for reducing 99 percent of the 77 most commonly found contaminants, but it’s unique in that it doesn’t filter out healthy minerals such as calcium, magnesium, and potassium. The three-stage filtration system works by first filtering out sediment, rust, and silt through the Sediment Pre-Filter. From here, the water goes through the Activated Carbon Claryum Filter to reduce pharmaceuticals, herbicides, pesticides, per- and polyfluoroalkyl substances (PFAS), and volatile organic compounds (VOCs). Finally, the Catalytic Carbon Claryum Filter uses National Sanitation Foundation (NSF)-certified Claryum technology to filter 97 percent of chlorine and chloramines, in addition to other contaminants including lead, mercury, asbestos, and cysts.

What’s more, this water filter has the fastest flow rate of all the filters on our list, powering through a half-gallon of water every minute, so you’re not stuck waiting on clean water. Additionally, the filters are very economical—they last for up to six months or 800 gallons, meaning you pay less than 10 cents per gallon filtered. However, those with limited cabinet space may want to consider another system on this list, as this under-sink water filter takes up a lot of space. And keep in mind that the system will not reduce total dissolved solids (TDS). 

The included metal faucet is available in brushed nickel, chrome, and oil-rubbed bronze, so you can choose which will best match your existing kitchen hardware and decor.

Price at time of publish: $450

Product Details:

• Filter Type: Sediment pre-filter, activated carbon filter, and catalytic carbon filter
• Filter Capacity: 800 gallons
• NSF-Certified: Yes

Who it’s for: People who need a space-saving under-sink water filter.

Who it isn’t for: People who want their water to go through multiple levels of filtration.

A budget-friendly option that’ll comfortably fit in any cabinet, the EcoPure Main Faucet Filtration System filters chlorine, sediments, and cysts incredibly effectively, and the easy installation means there’s no reason to get a professional involved. It uses a carbon-spun fiber filter to reduce contaminants, but it is worth noting that due to its compact size, water only goes through one stage of filtration.

Price at time of publish: $51

Product Details:

• Filter Type: Carbon-spun fiber
• Filter Capacity: N/A change filter every six months
• NSF-Certified: Yes

Who it’s for: People who don’t mind spending extra for heavy-duty filtration.

Who it isn’t for: People who need to filter well water.

The Waterdrop filtration system takes your tap water through a whopping eight stages of filtration, including a cotton layer to reduce large particles, an activated carbon filter for removing residual chlorine and odors, and more. However, the most important step in the filtration process is the reverse osmosis system, which reduces over 90 percent of TDS, in addition to heavy metals such as lead, arsenic, mercury, and cadmium. It’s also certified NSF 58 for TDS reduction and certified NSF 372 for lead-free material. And given the extensive filtration of this system, it offers a relatively fast flow rate—it can filter a cup of water in about 12 seconds.

Unlike many other RO systems, the Waterdrop filters water on demand without a tank, meaning it takes up less space in your cabinet. Reverse osmosis systems are also notorious for creating a lot of water waste (as much as four gallons of water “rinse” per one gallon of filtered water). Fortunately, the Waterdrop system has a drain-to-filtered water ratio of 1:1, significantly reducing water waste (and your water bill).  

The system comes with a smart and stylish faucet with a built-in LED display that will alert you as to when it's time to change the filter and display the quality of your filtered water. The reverse osmosis replacement filters run for nearly $90, but fortunately, only need replacing every two years. If you can swing it, the Waterdrop Reverse Osmosis Drinking Water Filtration System will leave you wanting for nothing.

Price at time of publish: $646

Product Details:

• Filter Type: Reverse osmosis
• Filter Capacity: 400 gallons
• NSF-Certified: Yes
  

Who it’s for: People looking for an affordable reverse osmosis option.

Who it isn’t for: People who tend to forget to replace the filter.

This reverse osmosis option is a little different from the Waterdrop G3 Reverse Osmosis Water Filter System in the sense that it’s not as heavy duty (aka, it doesn’t remove as many contaminants as the Waterdrop option), and it’s significantly more affordable.

Unlike most of the other under-sink water filters on this list, it doesn’t have a specific amount of water it can filter before you change the cartridge: In this case, you just have to swap it out every six months. Since there’s no auto-off function, you’ll have to remember to do this on your own, so if you’re the forgetful type, this may not be the best option for you.

Price at time of publish: $194

Product Details:

• Filter Type: Reverse osmosis
• Filter Capacity: N/A, change filter every six months
• NSF-Certified: Yes

Who it’s for: People who need to filter heavier components in water.

Who it isn’t for: People who don’t want to hire a professional to install their water filter.

This option is best suited for well water due to its advanced, dual-stage carbon block filtration system that removes heavier, larger contaminants from the water—such as particulate, chlorine taste and odor, lead, turbidity, parasitic protozoan cysts, VOCs, and methyl tert-butyl ether (MTBE). It has a large filter capacity of 625 gallons and a quick-change cartridge design, so you don’t have to turn off the entire system when it’s time to swap filters out. You will, however, need to professionally install this option, and it won’t help reduce mercury levels in water, if that’s a concern for you.

Price at time of publish: $395

Product Details:

• Filter Type: Carbon block
• Filter Capacity: 625 gallons
• NSF-Certified: Yes

Final Verdict

For most users, the Aquasana Claryum 3-Stage Max Flow is our top pick, thanks to its ease of use, fast filtration rate, and innovative multi-filtration technology. However, if you’re lacking the cabinet space and want a more affordable option, the EcoPure Main Faucet Filtration System comes a close second, thanks to its unique, space-saving design and DIY installation.

How to Shop for an Under-Sink Water Filter Like a Pro

Type

The type of filter(s) plays an important role in both the price and effectiveness of an under-sink water filtration system. There are generally three different types of filters available on the market, and the one you pick will most likely depend on your budget and the type of filtration you need. Here’s a quick primer on the different types of water filters: 

• Carbon Filter: A carbon filter is the most basic option when it comes to filtration, but still very effective. In this case, activated carbon will chemically bond with contaminants, removing them as water flows through the filter. However, all carbon filters aren’t created equal, so the effectiveness of a carbon filter alone will vary. You should look for the level of filtration noted on the product, including the contaminants it will remove.
• Reverse Osmosis Filter: The most heavy-duty option, reverse osmosis systems flush contaminants from the water supply to deliver filtered water through a separate faucet. The system works by pushing water through a membrane with pores that are incredibly small, so that only water molecules can pass through. This means that reverse osmosis filters are the most effective, with the ability to eliminate thousands of toxins such as chlorine, fluoride, and heavy metals, as well as bacteria and pesticides. However, many take up a considerable amount of cabinet space and are pretty difficult to install, which means you’re better off relying on a professional.
• Ultrafiltration: Ultrafiltration uses a hollow fiber membrane to stop debris and contaminants from entering the water. It’s not as effective as a reverse osmosis system, but it can preserve the healthy minerals that are eliminated in systems where only water molecules pass through. These systems are also easier to install, as they generally work as an addition to the existing faucet. However, in these cases, the filters will need to be changed much more often.

Filter Replacement

“Most filters need to be swapped every six months and cleaned periodically,” says Pinchev. “Due to this, I would recommend looking for options where the filters are relatively cheap and easy to purchase, and also allow easy access, so they can be cleaned without tearing the whole system apart.” After all, there’s nothing worse than buying an under-sink water filtration system, only to realize its preferred filter has been discontinued.

Installation

Most filters come with detailed instructions on how to install them, according to Lewin, and they’re usually easy enough to install on your own. However, if your setup requires you to drill holes in your faucets or valves, Lewin recommends you get professional help—provided budget isn’t an issue.

Questions You Might Ask

What are the benefits of an under-sink water filter?

“There are several benefits of installing an under-sink water filter as opposed to using a pitcher filter or whole-house water filter,” insists Pinchev. Below are some of his top few:

• They’re more convenient since you don’t need to keep refilling pitchers.
• They don’t take up valuable counter space, especially in small kitchens.
• The filtration is more targeted: It only purifies drinking water and doesn’t waste filtered water on washing dishes or showering.
• It affords better filtration than pitcher options because under-sink water filters use water pressure (not gravity) to push water through the filter.
• The cartridge doesn’t need to be replaced as often as a pitcher filter might (e.g. six months minimum versus two months).

How do you install an under-sink water filter?

Each system can be different, but overall, there are some general guidelines for installing an under-sink water filter, per Lewin. “If your sink doesn't already have a spare faucet slot, you'll need to drill one,” he says, reminding you to ensure that your water supply is turned off. “Once everything is prepared, locate your cold water pipe. Unscrew the pipe that connects the faucet to the cold water pipe, and connect the T-valve (usually included in the box) in the middle. Use Teflon tape around the threads on the connections to prevent leaks. Then, connect the plastic pipe and the shutoff valve (both usually in the box) to the T-valve.”

After this, you’re ready to put together the faucet by following the steps in the manual, which Lewin elaborates is usually the most difficult part. Once that’s done, however, all you have to do is mount the faucet on top of the sink.

How often do you need to change your under-sink water filter?

This will depend on the model you choose, but generally six months is the rule, says Lewin. Many options will also have auto-off functions or other indicators that’ll inform you when it’s time to change your filters, so you never have to worry you’re using an ineffective one.

“I usually recommend people ignore the estimated lifespan length and focus on the number of gallons,” adds Lewin. “You can then estimate how often you'll need to change the filter, based on your own family's usage.”

Take Our Word for It

This article was written by Nikhita Mahtani, a freelance writer with six years experience writing and editing for home publications. To come up with this list, Nikhita researched the best under-sink water filters and consulted Gabe Pinchev, founder and CEO of FieldPulse, an online platform for service contractors, as well as Paul Lewin, plumbing expert and founder of home maintenance blog Home Water Research.

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