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:

1. 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.

2. 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!”

3. 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.

What is reverse osmosis (RO)?

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?

1. 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.

2. 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.

3. 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.)