I watched a short documentary on youtube how NASA workers shop in a supermarket or order products, then get meals like spaghetti cooked at their facilities to be freeze-dried and vacuum-sealed for the ISS. Of course, many of the products they buy as a space food from contractors or simply buy commercial products and then repack those accordingly.

I won't post resources on space food as there are so many, but here is the video. They make a point that sending cargo to ISS is so expensive that the water is extracted in order to save money and space, but when you think about it it is a stupid argument because this water is needed onboard ISS. I haven't done research, but if I remember correctly only about 93% of wastewater is recycled on ISS and I believe water is regularly flown to ISS with cargo.

So what's the deal with the dry space food?

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It makes the food last a long time without refrigeration. (There are no food refrigerators on the ISS.)

Supply ship trips are not as frequent as driving down to the local grocery store.

Reference for the "no food refrigerators on the ISS" assertion

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  • $\begingroup$ Yeah, but the point it is done to save weight/money is misleading, right? $\endgroup$ – Nikolai Frolov Feb 16 '18 at 18:54
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    $\begingroup$ Needing no refrigerator also saves weight. $\endgroup$ – Uwe Feb 17 '18 at 9:42

Freeze-dryed food was used in the Apollo capsules and in the Space Shuttle. Electricity was generated with fuel cells using hydrogen and oxygen. The reaction product water could be used for dry food and for cooling. This dual use saved weight.

The ISS gets electricity from solar panels and not from fuel cells. But water is recycled on ISS and could be used for dry food again, see. You save weight also when less than 100 % of the water is recycled. If only 90 % is recycled, you need to replace and transport only the lost 10 %. Water is also used to get oxygen using electrolysis.

Therefore saving weight by using dry food was true for Apollo and the Shuttle, but is also true for the ISS.

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  • $\begingroup$ The water that comes with the food will result in less consumption of water by the crew and will eventually be recycled from air and urine, so there is no difference if this water had been shipped separately and used to hydrate food or is shipped with the food. How is this any cargo-weight gain? $\endgroup$ – Nikolai Frolov Feb 16 '18 at 22:32
  • $\begingroup$ The ISS is a closed ecosystem. Only the amount of water delivered matters. Why exclude it from food and ship it separately only to hydrate that food afterward, that's my point. $\endgroup$ – Nikolai Frolov Feb 16 '18 at 22:34
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    $\begingroup$ @Nigel The same water is used several times to hydrate food. To use the water again for food, dehydrated food is needed. There is no difference if the water is shipped together with the dehydrated food or in a separate transport. But if you ship hydrated food, much more water is to be shipped. $\endgroup$ – Uwe Feb 17 '18 at 9:41
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    $\begingroup$ If you don't recycle water, you have to ship 550 g in any way. But if you recycle water to 90 %, you need to ship only the 10 % of water with the food. You ship 50 g of water with 50 g of dry food, the remaining 450 g water needed to get the 500 g to wet the 50 g dry food are taken from the recyled water. The initial 500 g water have to be shipped to the ISS only once at first. $\endgroup$ – Uwe Feb 18 '18 at 9:03
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    $\begingroup$ If you ship wet food to the ISS AND recycle water on the ISS, you get more water than necessary and have to dump water from time to time. Shipping wet food requires additional weight for tin cans or the refrigerator. $\endgroup$ – Uwe Feb 21 '18 at 19:40

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