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Old 12-10-2024, 11:18 AM   #1
pzmcgwire
 
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Default Rations and Water

I'm looking at figuring out the load of rations and supplies that would be needed for survival.

It seems that most rations may not contain water needed for survival.

Meal Packs at 1 pound each appear to include water, but the more compact survival rations and higher tech food pastes don't seem to have enough mass for water.

Would a full life system be able to provide enough potable water for extended survival?

A battlesuited trooper or a sealed ATV is a closed system and if in a hostile environment where you can't crack seals, water is going to run out even if there is enough food pastes tubes.
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Old 12-10-2024, 11:35 AM   #2
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Default Re: Ratios and Water

In principle, a sealed system like a battlesuit should be able to continue more or less indefinitely on a finite water supply. Condense the moisture that's breathed and sweated into the air, filter the urine, dehydrate the feces, and you can reuse your water more or less indefinitely. In practice, none of this will actually be 100% efficient, so you'll still need to top up the supplies occasionally, but you can probably make it effective enough to keep water from being your limiting factor. (For reference, NASA was recently boasting about new technology increasing space station water recycling efficiency from 94% to 98%, albeit using equipment too bulky to carry around in a power suit; at higher tech levels, the systems will presumably be both more effective and more portable.)

EDIT: Note that food rations may potentially help make up lost water. Even if the rations are completely dehydrated, metabolism inevitably creates a certain amount of water (along with carbon dioxide) by breaking down organic molecules. In humans, the water so produced isn't nearly enough to survive on without drinking, but it could potentially be enough to make up for minor losses from a water recycling system that's not quite 100% effective.
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Last edited by ravenfish; 12-10-2024 at 11:42 AM.
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Old 12-11-2024, 07:57 AM   #3
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Default Re: Ratios and Water

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Originally Posted by ravenfish View Post
EDIT: Note that food rations may potentially help make up lost water. Even if the rations are completely dehydrated, metabolism inevitably creates a certain amount of water (along with carbon dioxide) by breaking down organic molecules. .
The body uses up more water during digestion than is produced when metabolizing dry food.
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Old 12-11-2024, 10:23 AM   #4
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The body uses up more water during digestion than is produced when metabolizing dry food.

Yes, but most of the water "used" isn't destroyed as such, but rather excreted and so on. From the point of view of wilderness survival or ordinary nutritional budgeting, it's a loss either way; in the context we're discussing, of technological closed-system water recycling, it remains potentially available.
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Old 12-11-2024, 05:13 PM   #5
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Default Re: Rations and Water

Any environment that has hydrogen and oxygen can provide water with the appropriate technology.
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Old 12-21-2024, 01:20 PM   #6
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Default Re: Ratios and Water

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Note that food rations may potentially help make up lost water. Even if the rations are completely dehydrated, metabolism inevitably creates a certain amount of water (along with carbon dioxide) by breaking down organic molecules.
No, that's backwards. Digesting food consumes water. Organic molecules are generally hydrolyzed to split them up, which requires water.

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Originally Posted by ravenfish
Yes, but most of the water "used" isn't destroyed as such
It is, actually. Water is split into an H and an OH group, and those groups are attached to other molecules to break bonds- that's hydrolysis.

Some foods require more water than others. Proteins are split into amino acids via hydrolysis, but then some are recombined to make new body proteins, thus scavenging some of the water used for initial hydrolysis. But when carbohydrates are hydrolyzed most of the resulting sugars are burned to make energy, and those H2O atoms ultimately end up split up onto other molecules, much of them excreted as waste. That's why you get thirsty after a big carb load- there is a net loss of water. Yes, glycogenesis and such processes can release water (as can producing fat) but then the glycogen needs to be hydrated with quite a lot of water to be stored. That's why marathon runners end up a few pounds lighter at the end of the race- not from the glucose used, but rather by releasing (and excreting) the water in their livers that's used to store glycogen.

This stuff all ties in together and gets complex. Here is the metabolic chart that you more or less memorize in advanced biochemistry classes. But the bottom line is that digestion does not produce water- it consumes it.

Last edited by acrosome; 12-21-2024 at 01:47 PM.
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Old 12-21-2024, 07:53 PM   #7
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No, that's backwards. Digesting food consumes water. Organic molecules are generally hydrolyzed to split them up, which requires water.



It is, actually. Water is split into an H and an OH group, and those groups are attached to other molecules to break bonds- that's hydrolysis. [....]
Granted, but the subsequent metabolism of the simple compounds produces water (at least assuming aerobic respiration rather than one of the weird fermentation pathways).
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Old 12-22-2024, 06:04 AM   #8
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Granted, but the subsequent metabolism of the simple compounds produces water (at least assuming aerobic respiration rather than one of the weird fermentation pathways).
At a basic level, starting from starch, hydrolysis consumes one water molecule for each glucose molecule produced. Glycolysis turns each glucose molecule into two pyruvate molecules and two water molecules. Each pyruvate molecule then goes through the citric acid cycle, which consumes three water molecules and produces one.

Let's say you start with a 10-chain starch. You use up 10 molecules of water and produce 10 molecules of glucose. Those then become 20 molecules of water and 20 molecules of pyruvate. The pyruvates consume 60 molecules of water and produce 20 via the citric acid cycle. So you wind up using a total of 70 molecules of water and get 40 back, for a net loss of 30.

There's a reason bread makes you thirsty when you eat it. Actually, my experience is that just about anything other than juicy fruits (which provide quite a good deal of water on their own) makes me thirsty when I eat it.
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Old 12-22-2024, 09:06 AM   #9
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At a basic level, starting from starch, hydrolysis consumes one water molecule for each glucose molecule produced. Glycolysis turns each glucose molecule into two pyruvate molecules and two water molecules. Each pyruvate molecule then goes through the citric acid cycle, which consumes three water molecules and produces one.
You've forgotten the Electron Transport Chain, and the fact that the NADH and hydrogen ions produced in the citric acid cycle will react with oxygen to produce water. (Frankly, biochemical pathways are more than I really wish to deal with at this stage of my life, so I prefer zoom out a bit and realize that, if a glucose molecule is reacted with oxygen, the net product will be six molecules of carbon dioxide and six molecules of water, irrespective of what crazy path they take to get there and whatever crazy catalysts are involved.)

I strongly suspect that the primary cause of thirst on eating is the fact that the physical aspect of digestion requires lots of water to be secreted (in saliva, gut fluids, and so on) to get the food into a form from which the nutrients can be absorbed (along with the fact that some of the more interesting products of breaking down organic molecules will need to be removed from the body by urination, with the inevitable use of water that this entails).
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Old 12-10-2024, 12:00 PM   #10
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I'm looking at figuring out the load of rations and supplies that would be needed for survival.

It seems that most rations may not contain water needed for survival.
I suspect all of them need some supplemental water.
Quote:
Originally Posted by pzmcgwire View Post
Would a full life system be able to provide enough potable water for extended survival?
Water recycling is fairly straightforward, but it's also not too difficult to get it safely through a seal if environmental water exists at all.
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