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What’s the best water filter for removing toxic PFAS?

Many in-home drinking water filters may not remove the most concerning contaminants.

In antiquity, “crazy as a painter” was a phrase borne from the demented behavior of lead-poisoned painters. Before the use of mercury was banned in the 1940s, hat makers used it in their craft, leaving many mileners “mad as a hatter.” Women used to use arsenic for their complexion; and we used to impregnate children's wallpaper with DDT.

Doesn't that all sound nuts? Like, what were we thinking? The answer is that we didn't know any better. Unfortunately, we are still at this kind of toxic tomfoolery – and even worse, we know what we're doing now, and we're doing it anyway.

Which brings us to per- and polyfluoroalkyl substances, commonly known as PFAS. Used in a wide array of commercial applications since the 1950s – think firefighting foam, non-stick pans, and water-repellents – the family of chemicals has come under scrutiny because they accumulate in organisms (like humans) and remain in the environment indefinitely. You may have heard them referred to as “forever chemicals.”

They are widespread and exposure to them is associated with various cancers, low birth weight in babies, thyroid disease, impaired immune function, and many other health problems.

And they are especially present in drinking water. “The chemicals have been detected in the drinking water of more than six million Americans at a level exceeding the Environmental Protection Agency’s (EPA) 2016 lifetime drinking water health advisories level of 70 parts per trillion (ppt) – a level seven to ten times greater than the safe level of exposure estimated by the Centers for Disease Control and Prevention (CDC) in 2018,” notes the NYU School of Law.

Since the current administration doesn't seem all that concerned about clean water (read more about that at the NYU link above), it's up to us to protect ourselves. So we go out and get our filters, imagining that all that toxic gunk will be removed from our water, but alas. As a new study from Duke University concludes:

“The water filter on your refrigerator door, the pitcher-style filter you keep inside the fridge and the whole-house filtration system you installed last year may function differently and have vastly different price tags, but they have one thing in common,” writes the University. “They may not remove all of the drinking water contaminants you're most concerned about.”

The study is the first to look at how well residential filters do in removing PFAS.

“We tested 76 point-of-use filters and 13 point-of-entry or whole-house systems and found their effectiveness varied widely,” said Heather Stapleton of Duke's Nicholas School of the Environment.

The authors conclude that any filter is better than none, but many filters are only partially effective at removing PFAS from drinking water. And some, if not properly maintained, can make it even worse.

The winner of the bunch were under-sink reverse osmosis and two-stage filters. Stapleton said:

All of the under-sink reverse osmosis and two-stage filters achieved near-complete removal of the PFAS chemicals we were testing for. In contrast, the effectiveness of activated-carbon filters used in many pitcher, countertop, refrigerator and faucet-mounted styles was inconsistent and unpredictable. The whole-house systems were also widely variable and in some cases actually increased PFAS levels in the water.

The reverse osmosis filters and two-stage filters they tested reduced PFAS levels by 94 percent or more in water. Activated-carbon filters removed 73 percent of PFAS contaminants, on average, but results were quite mixed. “In some cases, the chemicals were completely removed; in other cases they were not reduced at all.”

Whole-house systems using activated carbon filters also presented very mixed results. “In four of the six systems tested, PFSA and PFCA levels actually increased after filtration. Because the systems remove disinfectants used in city water treatment, they can also leave home pipes susceptible to bacterial growth,” notes Duke.

So, reverse osmosis filters and two-stage filters for the win. But even so, the real win would be controlling PFAS contaminants at their source in the first place. But humans are a species filled with folly – we may not have crazy painters and mad hatters anymore, but watch out for that tap water.

The research was published in Environmental Science & Technology Letters.

Many in-home drinking water filters may not remove the most concerning contaminants.