>It's not an urban legend.

I agree, it's more like a legend for the underdeveloped world, especially the more rural parts which suffer from all kinds of deficiencies.

Of course I'm going to take it "with a grain of salt" when one of the authors' introductory bullet points is

Distilled water has poor taste characteristics.

Which I have long known to be patently false, regardless of the hundreds of sources of demineralized water I have enjoyed or been responsible for. In a properly functioning system, poor taste has never been a characteristic ever.

Although I'll admit you have to know how to run a still.

Theoretically each "insoluble" mineral like mercury or lead is regarded that way because they commonly form various compounds which various chemists throughout history have tried to dissolve in otherwise mineral-free water.

These compounds are considered insoluble since you can put in a gram to a liter of DI water, stir it all you want, filter out what didn't dissolve and get back a whole gram.

Or you can put in a millgram and get back a whole milligram.

That's not the kind of everyday behavior you're going to get from compounds of Sodium, Potassium, Calcium & Magnesium. These life-giving minerals are very soluble by comparison to the life-compromising minerals like mercury & lead.

Many milligrams up to many grams of these good mineral compounds like potassium can easily dissolve in a liter of mineral-free water.

But nobody would drink mineral water that strong, it would taste worse than sea water.

However in fact when there is no mineral shortage there is also no significant difference in the amount of the good minerals that will dissolve in most average tap water versus DI water.

Therefore unless your primary source of beneficial minerals is from water alone, the difference between drinking mineral-free water versus tap water or even stronger popular mineral waters will not be mathematically measurable in a meaningful way.

Your total mineral intake relative to outflow is what determines your position on a spectrum of dynamic equilibrium for each mineral, regardless of whether the minerals come from water or food. This is not a complex concept, you wouldn't do a marathon any better on tap water than DI water when you really need something like Gatorade at least.

You really can never let the life-giving minerals become depleted down to your last milligrams or you would be dead. And no mineral water alone is enough to replace the normal amount you need coming through your system. That's why Gatorade was invented for those extreme times.

So almost everybody has always gotten most of their essential everyday minerals from their food, and unless the water has some beneficial minerals that the food does not, it makes no difference if it was replaced with DI water instead.

Water-soluble vitamins are not much diferent and need to be constantly replaced to maintain a good level, that's why Vitamin Water was invented in later decades as the food got bleaker, and you're not likely to get tap water with vitamins anytime soon.

Maybe I shouldn't give anybody any harebrained ideas for a startup.

OTOH with toxic minerals which you might want to flush out of your system, things like mercury or lead are actually saturating the water when you try to dissolve a milligram so they're not truly insoluble, you just can't measure the infintesimally miniscule amount that actually did dissolve before the water became saturated and will take up no more of that particular mineral.

But these are harmful minerals where micrograms are undesirable, and known to accumulate in living things, which can somewhat be attributed to their near-insolubility so if there's any hope of preventing or reducing any long-term accumulation it would have to be somewhat dependent on excreting more than is imbibed over the long term instead. No quick answer could ever be expected.

Because picograms add up to nanograms, and nanograms add up to micrograms and before long it's like Flint MI if your're not careful.

Mostly the rest of the time it's basically unmeasurable until something like that rears its ugly head.

Now when water has been subjected to a highly effective distillation or demineralization process which theoretically removes all minerals by orders of magnitude, and it turns out true in practice for those minerals which are measurable, you can have some confidence that the process will also affect some toxic minerals that might be present in unmeasurable amounts, and reduce them to even further levels of unmeasurability.

There's equations for all of this.

When the concentration of any barely soluble compound actually equals zero it's difficult to quantify the increase in solvent strength compared to nonzero, but I can live with it.

So I'll drink to that.