The label on my 91% Isopropyl says the other 9% is distilled water. Since we’re all diluting our various alcohol formulations with distilled water anyway, why does 9% already added make Isopropyl unsuitable? Does it contain other impurities? Is the distilled water it contains not distilled enough?
Not criticizing, seeking knowledge.
BTW, have you tried making coffee with distilled water? It’s quite different: pure coffee flavour, with no added mineral tastes. I love it... but coffee is a very personal thing...