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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?

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  • $\begingroup$ What if there was no other water supply but the one inside a self-sufficient space settlement, then how would the water be mineralised? $\endgroup$ – loceteg166 Feb 6 at 20:43
  • $\begingroup$ @loceteg166 some methods are suggested here: adding a pinch of a salt, or running the DI water through a bed of crushed limestone or dolomites. There might be another ways to add required ions (Ca, Mg, etc), but I'm not an expert in chemistry to suggest what these other ways might be. $\endgroup$ – Sergiy Lenzion Feb 6 at 20:56
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There are six types of water on the ISS (nothing on the ISS is simple!)

enter image description here

Note that the potable water has minerals added "for taste".

The shuttle water system added iodine to its potable water by running fuel cell product water through a microbial filter. Minerals were not added to the shuttle potable water.

enter image description here

The US iodinated water and the Russian silver-biocide treated water are incompatible; if they mix a precipitate forms. Back in the shuttle days, the US water supplied to Mir and the ISS from the shuttle fuel cells had to be processed to remove the iodide.

References

The ISS: Operating an Outpost in the New Frontier pp. 340-344

Environmental And Life Support Systems Training Manual pp. 5-1 and 5-2

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    $\begingroup$ Incidentally, the ISS document linked has the first decent description of the ISS systems with schematics for the intelligent layperson that I've seen NASA produce, similiar to the old shuttle press reference manual. $\endgroup$ – Organic Marble Jan 12 at 14:18
  • $\begingroup$ Thank you for the answer. Based on info from the table, it looks like only water recycled through the Russian module is used for drinking. I'm still confused with how exactly the water mass balance is arranged. For example, I've since found this article that claims Americans and Russians have separate sources of drinking water. I thought they meant sources of fresh water. But after re-reading I'm not sure, maybe they meant recycled. $\endgroup$ – Sergiy Lenzion Jan 14 at 8:50
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    $\begingroup$ It's complex and I'm not an expert on it, especially the Russian side. The document I linked goes into pretty good detail on the water systems, you might enjoy reading that part of it. $\endgroup$ – Organic Marble Jan 14 at 13:40

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