Sure, but it works :) (except that one company that had a low quality membrane that leached ionomers, lol). Once plastics have leached off their manufacturing chemicals they really are very benign.
The membranes you mention are permeable, basically, only to water. Salt ions are pretty small - if the membrane blocks salt ions, they're going to block just about any molecule [1].
1. for the most part. You can have a molecule that dissolves in the polymer membrane and therefore gets through. A great example is polymer self-diffusion itself (fairly slow) and very short chains of the polymer (faster). But, generally, polymers don't like to mix with anything but themselves (see Flory-Huggins and DeGennes).
My daughter just told me, "If you really stretch it, you can make what you post on social media true."
Alas, I must concede the point: upon actual cursory research, drinking distilled water is NOT a health risk.
(I was once admitted to hospital because of crazy electrolyte levels, while presenting other symptoms as well. Is long story. Perhaps it's time for me to stop worrying about potassium...)
Its not just a US thing, other places in the world have fluoride in their water. In many areas fluoride just naturally occurs in the water at levels even higher than what managed services target. But other countries, such as Hong Kong, parts of Malaysia, Singapore, Ireland, parts of Spain, parts of the UK, parts of Canada, Mexico fluoridates table salt, most of Austrailia, Fiji is rolling out a program, half of New Zealand, about half of Brazil, and most of Chile all have some water fluoridation programs. Many other countries did at some other point in time but stopped doing it.
The membranes you mention are permeable, basically, only to water. Salt ions are pretty small - if the membrane blocks salt ions, they're going to block just about any molecule [1].
1. for the most part. You can have a molecule that dissolves in the polymer membrane and therefore gets through. A great example is polymer self-diffusion itself (fairly slow) and very short chains of the polymer (faster). But, generally, polymers don't like to mix with anything but themselves (see Flory-Huggins and DeGennes).