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Best Under Sink Water Filters
Under Sink Reverse Osmosis (RO) and non-RO water filters for your kitchen or bathroom. Only systems that are independently tested, show results with reduction %s, and how many gallons they maintain that % for, are listed. Scroll to the bottom for more on all the water filter acronyms, vocab, and details.
Under Sink Reverse Osmosis Filters
Cloud
Cloud is the best under sink reverse osmosis filter. It is NSF 58 certified (NSF 58= RO testing!) by NSF itself, which means it’s been verified to remove 98% of TDS, chlorine, and much more for 400 gallons. It also remineralizes the water, which is very important. A real-time sensor monitors your water quality so replacement filters are sent when needed, not on an arbitrary schedule. It has lower water waste than other RO systems (54% recovery rate!) Self install, including a separate tap, which I prefer for under sink RO because it’s easy to blow through 400 gallons if you’re using RO water for everything through your regular faucet.
Their specs are almost as impressive as the Cloud, but this is more affordable, and Aquasana does a great job of displaying their NSF 58 test results— this model is certified by WQA to remove 96% of TDS (everything that’s not water; read more below) for 365 gallons, and remineralizes the water as well, something I consider essential for RO. Recovery rating is 42.8%. No app or water quality monitor, but it does alert you to change the filters every 6 months. Self install, including the separate tap, which comes in a few different finishes.
Only 2 RO filters? So far, yes. I’ve also considered Waterdrop, APEC, Culligan, Sorso, and iSpring, but none meet all 3 of my requirements, even with pesky emailing.
Under Sink Non-RO Filters
This removes 99% of chlorine, PFAS, VOCs, BPA, pharmaceuticals, and more for 800 gallons, certified by WQA. The main difference between this and the Clearly Filtered version is that this has a separate tap, which may mean you can replace filters less often. A separate tap allows you to use it just for drinking and cooking water, not for washing dishes or your hands. This is what I use in my own kitchen.
The 3-Stage Under Sink System reduces a long list of contaminants like chlorine, PFAS, VOCs, and more by 90-99% for 2,000 gallons. This is their only under sink model, and it connects inline with your current faucet, so you don’t need to install a separate tap. Self-install with a wrench. Removes fluoride almost as well as an RO system, which is a unique feature.
I’m a little skeptical how much Hydroviv actually changes their filtration media based on your zip code’s city water data, since there are only a handful of types of filtration media that exist. An email conversation with them didn’t clarify much. That said, they do have NSF testing and certification for removing chlorine and chloramine for 600 gallons, lead and PFAs for 600, and VOCs for 360 gallons. Nothing else has been verified. It’s hard to know if changing the media based on your zip code would change these results. Connects directly with your existing faucet line.
This is surprisingly similar to the effectiveness level of both 3-Stage filters listed above; it’s verified to remove 95-99% of chlorine, chloramine, lead, PFAS, VOCs, BPA, other pharmaceuticals (and much more) for 784 gallons. 784 gallons is about 36 days of regular faucet use, including dishes and washing hands, and while the filter will still work after that, it won’t necessarily be doing so at 99%. If you keep up with filter replacement, this is still a solid choice for its affordability, ease, and verified effectiveness.
Why do you have 3 requirements for water filters?
In short, because there are no federal regulations for water filters, and it is an industry rife with healthwashing— no one should be tricked into thinking their water filter is doing more than it is. That’s especially important considering the state of drinking water in the US (not great). These are my 3 requirements for recommending a water filter, and why:
Testing done by an independent lab: a surprising number of water filter brands have never had their filters tested. Some have done in-house testing, but the conflict of interest is obviously high. So, I look for independent testing done by a third party lab. I prefer when that third party is one of the “big 3” accredited water testing labs (NSF, WQA, IAPMO) but in order for you to have more than one choice, I also include filters with third party testing done by a private industry lab, as long as they meet the next two requirements, as well.
Test results are shared with a list of contaminants and % reduction: this is important because “NSF-42 certified” just means that a filter can reduce “aesthetic impurities like chlorine and taste/odor” by at least 50%. I prefer to see that both chlorine and chloramine were tested, and what % they were reduced by— hopefully in the 90%+ range! The same goes for any claim— I’d like to see exactly what “heavy metals” were reduced, and by how much, not just “REMOVES HEAVY METALS FOR YOUR HEALTH!”
Gallons the testing was done for: this is the trickiest one! It’s so important, and most brands either don’t do this testing or don’t share the results! For example, just because a filter can remove 99% of PFAS, it doesn’t mean it can do that for very long. Does it remove 99% of PFAS for 100 gallons or 2,000 gallons? Another example, if an RO system can remove 96% of TDS at a rate of 30 gallons a day, that’s great, but for how many days? How do they know that a filter needs replacing at month 6 without having tested this? And so on.
What is TDS?
TDS means Total Dissolved Solids. There are a lot of dissolved solids in water— salts, metals, minerals, and contaminants. Put another way, TDS is everything in the water that isn’t hydrogen or oxygen (H2O), because if you can remove these tiny salts, it means the filter is working well enough to remove basically everything else. A reverse osmosis filter works by removing the TDS and keeping just the H2O molecules.
RO is a water purification process that uses a semi-permeable membrane to remove almost everything from water except for extremely tiny gaseous elements and water molecules (Hydrogen and Oxygen, also known as H2O). It uses pressure to force water through a membrane, keeping toxins, bacteria, chemicals, minerals, and heavy metals on the other side. RO systems usually also include an activated carbon filter to capture the very-tiny gaseous elements like VOCs and chlorine.
What is NSF 58?
This is a certification that verifies an RO filter works. It means the RO filter is able to remove at least 75% of total dissolved solids (TDS) that pass through it. TDS is anything that is not a hydrogen or oxygen molecule—so, anything that is not water. When a filter has a high TDS, as certified by NSF 58, it means you can generally assume it is also capable of filtering out lead, hexavalent chromium, cadmium, fluoride, VOCs, radium, asbestos and PFAS. (However, a company cannot explicitly claim it removes all of those things without also specifically testing for these things.)
What is the most effective water filter?
Reverse osmosis is the most effective type of water filter. It captures the greatest number of water contaminants. It’s not necessarily the best choice for everyone in every living situation at every price point, but very broadly speaking, it is simply the most thorough technology that we have to purify water.
What are the disadvantages of RO?
Water waste: depending on the brand, for every 1 gallon of pure water created, RO wastes 1-5 gallons of water. In general, whole-house RO wastes more than under-sink RO. The two I have listed waste about 2 waste gallons for every 1 pure gallon.
Demineralization: RO is so effective at removing everything from water, it also removes trace minerals important for keeping you alive, like sodium, potassium, and magnesium! It’s very important to drink these minerals, so an RO system that remineralizes water for you is important. The ones I have listed above all remineralize the water for you.
Expense and maintenance: RO systems are generally more expensive to install and maintain. This is more true for whole-house RO than under-sink RO, as under-sink RO is getting better and more convenient quickly.
How should I choose between a reverse osmosis and non-RO water filter?
If you are comfortable with the disadvantages of RO, listed above, or have ways to counteract them, like saving water in other ways, then RO may be the best fit, as it will remove the most contaminants.
If not, a non-RO filter will still do a lot of good!
If you’re on the fence, you should check your city’s water data— or even better, test your own tap water with a kit so the results include what’s going on in your house’s pipes— so you know what water contaminants you’re dealing with and can make a more informed decision. For example, if you find out your water has a high level of hexavalent chromium that you want to remove, RO will be the best option. If you’re more concerned with removing chlorine, a non-RO activated carbon system will do just fine.
What can RO remove that carbon and ion exchange can’t?
RO can remove almost every water contaminant— as long as it’s tested and certified to be able to at a high percentage. It is much better at removing cysts, hexavalent and trivalent chromium, arsenic, nitrates and nitrites, cadmium, lead, barium, fluoride, copper, asbestos, perchlorate, radium, and selenium than non-RO (carbon and ion exchange.)
What is a non-RO water filter made of?
Typically, these are a combination of activated carbon and ion exchange material…
What is activated block carbon?
Activated carbon attracts and removes water impurities. How well the carbon removes them depends on how long the impurities are in contact with the carbon. If water wooshes by too quickly, or there’s not much carbon surface area to come in contact with, it won’t remove much. Block carbon is carbon formed into a block under high pressure. It has a high surface area, so is able to remove many more contaminants than looser, granulated carbon.
A high quality block of carbon that is certified can remove up to 99.9% of many VOCs, arsenic, antimony, beryllium, fluoride, selenium, thallium, and uranium.
What is ion exchange?
Ion exchange is a type of filter with a material attracts harmful negatively or positively -charged contaminants, and exchanges them for harmless negatively or positively -charged minerals, like sodium or chloride (basically, salt molecules). It’s very effective at removing some of the things that carbon filters can’t capture.
Ion exchange technology that is certified can remove arsenic, hexavalent chromium, cyanide, nitrate, perchlorate, PFAS, sulfate, barium, radium, strontium, and uranium.
Where can I look up water filters to see if they have certification and testing?
The big 3 are NSF, WQA, and IAPMO. You can easily search the brand name in their databases to see what the testing done was:
IAPMO: https://pld.iapmo.org/
You can also email the brand directly— even if they give you the runaround, and get an unsatisfying answer, you’re still sending a message that this matters.
What is NSF?
It’s so boring— it stands for the National Sanitation Foundation. But it’s good that it’s boring! It is an independent, third party testing company that protects you, making sure that the claims a water filter company makes are true. NSF Certification means that NSF has tested the product, verified that the claims match the results, and can pop by anytime for a surprise inspection to make sure the quality stays high.
For water quality, the NSF has strict criteria for certification— for example, a filter must be able to reduce chlorine by 90% at a certain flow rate, for a certain number of gallons (typically 3 months worth of showering) for it to qualify for NSF-177 certification. If the filter only reduces chlorine by 80%, or can’t do it at a typical shower flow rate, it doesn’t qualify.
What does “tested to NSF standards” mean?
If you see the phrase “tested to NSF standards,” rather than “tested and certified by NSF,” this means the company has either tested the product themselves, sent it to a private lab, or sent it to a verified third-party lab that isn’t NSF, for testing. This happens for a few reasons:
NSF testing and certification can be expensive to maintain, and a start-up company may not have funding for this, even though their product is truly able to do what they claim. In this case, they may test it themselves, or send it to a less expensive private lab to show that it performs well. This may be done in good faith, or it may be done irresponsibly, and at less high of a standard than NSF would. That distinction, and whether or not you trust them, is up to you!
If a company’s water filter cannot meet NSF standards, they may purposely send it to a verified third party lab like WQA or IAPMO to gain verification that it comes close to meeting NSF standards, isn’t quite there, but still want to show transparency. For example, it’s very hard for a shower filter to meet both flow rate requirements set by states and filter out the NSF standard for PFAS. So, a brand may take their filter to WQA or IAPMO to show that while it doesn’t meet the NSF level, it still meets the highest level possible at a regular flow rate. WQA and IAPMO are both reputable third party testing labs that use standards similar to NSF to guide their work.
What is WQA?
WQA stands for the Water Quality Association. Their “Gold Seal” certification is actually the oldest third-party testing and certification program in the water treatment industry.
What is IAPMO?
IAPMO stands for the International Association of Plumbing & Mechanical Officials. Like NSF or WQA, they are a trusted third party lab that have long been a national standard in legitimate third party testing for water quality and protecting consumers.
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