Rations and Water

[pzmcgwire]

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.

[ravenfish]

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.

[Anthony]

Originally Posted by pzmcgwire

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.

Originally Posted by pzmcgwire

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.

[Rupert]

Originally Posted by pzmcgwire

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.

None of then can include more than incidental water, given their weights. Even 1 pound per meal packs don't - meal packs have heating and cooling packs, etc., and are supposed to be reasonably balanced and to provide enough energy for active adventurers and the like. That means at over a pound of protein, sugars, and fats a day, plus fibre, micro-nutrients (some not so micro), and so on. Once you account for the packaging and sundries, you'd be lucky to have a pint of water, and a active person needs a great deal more than that, even in a temperate climate.

[DanHoward]

There was a Pyramid article that covered most of this:

Rationalizing Rations by S.E. Mortimer, November 5, 2004

[DanHoward]

Originally Posted by ravenfish

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.

[Varyon]

Originally Posted by Rupert

None of then can include more than incidental water, given their weights. Even 1 pound per meal packs don't - meal packs have heating and cooling packs, etc., and are supposed to be reasonably balanced and to provide enough energy for active adventurers and the like. That means at over a pound of protein, sugars, and fats a day, plus fibre, micro-nutrients (some not so micro), and so on. Once you account for the packaging and sundries, you'd be lucky to have a pint of water, and a active person needs a great deal more than that, even in a temperate climate.

GURPS has characters requiring 4 lb (2 quarts) of water every day in temperate climates (more in hotter and drier ones), which makes it pretty clear that a 1 lb meal pack cannot contain a meal's worth of water (even if it were nothing but water, you'd still be a pound shy each day).

Characters need to carry water separately. At TL9+, this can be potentially avoided (at least partially) with technology. The Vapor Canteen and Vapor Collector, both TL 9, can keep you in potable water so long as the environment isn't too dry. The Desert Environment Suit (TL 9) is akin to a Dune Stillsuit, reducing water needs to 10% normal (a bit less than a cup a day rather than needing 2 quarts a day). The Expedition Suit (TL 10) is more advanced and drops things to 5% normal (3.2 oz a day). I think the Cutting Edge and Ultra Tech armor design articles from Pyramid have options to include this functionality in armor, but I may be misremembering. Even in a relatively arid environment, the combination of a Stillsuit of some sort and a Vapor Canteen will probably keep you going for as long as the power cells hold out (bring a solar panel array and camp out beneath it during the day, or put some solar paint on your Stillsuits, and you can probably keep those fully charged for quite some time).

Note in some environments you can get away with just having something to carry water in (although some sort of filtration system is a good idea), as you can refill it when you come across streams, rivers, etc. But that's not automatic, and I believe typically requires a successful roll against Survival.

[ravenfish]

Originally Posted by DanHoward

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.

[Donny Brook]

Any environment that has hydrogen and oxygen can provide water with the appropriate technology.

[Polydamas]

Apparently one issue with ISS recycling is keeping contaminants from building up in the water supply. Science fiction often brushes over these obstacles, but for worldbuilding its good to know that getting rid of bad things can be as difficult as not losing good things.

Originally Posted by pzmcgwire

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.

I don't think any GURPS rations include the water you need for drinking and washing. Some GURPS rations may require additional water to be added for cooking, increasing shelf life but just changing the supply problem.