"All of the under-sink reverse osmosis and two-stage filters achieved near-complete removal of the PFAS chemicals we were testing for,” Stapleton said. “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.” - https://nicholas.duke.edu/news/not-all-home-drinking-water-f...

Note that the multistage RO filter can be a countertop one. It doesn't need to be an under-sink one. Just remember to change the filters on time.

Another thing that people overlook about RO is that it's critically essential to remineralize it safely and to normalize its pH. Drinking demineralized or acidic RO filtered water is harmful!

> Drinking demineralized or acidic RO filtered water is harmful!

What is the evidence for that? I drink homemade distilled water without any remineralization steps and it's perfectly fine.

Also note that pure water becomes slightly acidic from absorbing carbon dioxide in the air, producing carbonic acid. https://en.wikipedia.org/wiki/Carbonic_acid#In_biological_so...

There are at least three concerns from demineralized or acidic drinking water:

1. Drinking demineralized water results in an obvious multi-mineral deficiency, considering that we actually rely on drinking water for meeting a meaningful subset of our calcium, magnesium and other mineral intake. Even moderate supplementation won't correct it -- it takes a double dose to prevent it under RO.

2. Demineralized water causes minerals to be leeched from the body, also from the bones. This is to balance the water. It would also stress and deplete the bicarbonate reserve of the body to neutralize its acidity.

3. The extreme solubility of demineralized water unnaturally increases the absorption of heavy metals from foods and supplements which would otherwise go unabsorbed.

As for acidic water, it's straight-up bad for the kidneys, bones, and the spleen. It will boost the odds of kidney stones, weak bones, and a deteriorating immune system. Try measuring the urine pH to realize the effect. Granted, bicarbonate will buffer it, but the body's capacity to do this is fairly limited.

I was thinking the same thing. The chamber holding the activated carbon is probably lined with plastic

But probably not one with PFAS

They can and do. However I believe RO filters, which are made from plastic, leach microplastics into the water they filter.

You need a evaporation/condensation system to get guaranteed pure drinking water.

A multistage RO unit has an activated carbon layer after the RO layer. This AC layer is intended to capture the nanoplastics leaked from the RO layer. Moreover, if the RO layer gets replaced on time, the nanoplastic leakage is more limited. Certainly though I could use studies about how well or poorly this works.

I would believe so. But someone that better understands the PFAS molecules should confirm.