I was thinking the same thing -if I used tap water, wouldn't the fluoride and other impurities just get into the mag oil?
But, when using bath flakes in a bathtub or foot bath - isn't the same thing happening? It's being mixed with tap water and one is soaking their feet or body in the mixture. If this is the case, why should it be so bad to make mag oil with tap water? Isn't it the same thing as taking a bath with the flakes? The Ancient Minerals website simply says to run water with the flakes...nothing about distilled water. What do you think?