This question and answers to it contain wealth of information regarding recycling of ISS resources, and water is one of them.
Water, recycled from water waste, atmosphere moisture and urine, is virtually totally demineralised. Iodine is then used as a biocide treatment.
But what about minerals (magnesium, calcium etc.)?
As far as I know, there are two conflicting opinions: one claims that drinking only demineralised water would "wash away" minerals from the body (i.e. would not replace the minerals lost through sweating and urine with minerals otherwise naturally present in potable water), the other says it's ok as minerals would come in with food anyway.
So, having the water recovery system that "feeds" demineralised water for the crew consumption, how exactly is the minerals balance handled on ISS?
Do they mineralise the reclaimed water somehow before astronauts consuming it, or maybe the food is "pre-packed" with an additional amount of minerals (equal to the lost amount), or is it enough to just take a pill with the minerals when drinking/eating?
If it's the latter two, would it be the same from metabolism point of view (i.e. how completely are minerals "absorbed" by human organism when concentrated in food/pill compared to smaller concentrations of minerals consumed over longer period of time with potable water)?
Bonus question: Apollo astronauts did drink demineralised water being a bypass product from reaction in fuel cells, and afaik Space Shuttle produced drinking water from fuel cells too. Was minerals balance a problem/consideration at all in these missions?