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In battlestar galactica season 1 episode 2 their watertanks were sabotaged and they lost

Almost 60% of total potable water reserves.

The rest of the episode were them looking for more water. Their supplies were announced to last for a very limited amount of time. (A week or two?)

But earlier in the episode, it was stated that

Galactica's water recycling system is close to 100% effective. For all intents and purposes, there's not a drop of water that's wasted aboard.

ADAMA: We have enough water for several years before replenishing.

What could possibly consume the rest of the water in such a short period of time?

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    Is it possible that of the 100% of all water on board, 60% was "free" water and the other 40% locked up in recycling, or aquacultures, toilets or in bodies on the ship? Now, losing nearly 60% of your water seems more like 0% water and it might make more sense they only had a couple weeks worth.
    – coblr
    Commented Mar 6, 2017 at 21:12
  • It would have trouble running out of water because it recycles efficiently and loses none
    – Mawg
    Commented Mar 7, 2017 at 10:42
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    Your body is quite capable of recycling 100% of its blood, but if you suddenly lose 60% of it, you're still going to have issues.
    – Erik
    Commented Mar 8, 2017 at 10:21
  • If you drink out of a jar, then pee into the jar, in a recurring cycle - at anything less than exactly 100% reclamation, you're eventually going to run out of water. Now imagine someone comes along and kicks your jar over, pouring 60% of it out onto the ground before you can pick it up. Even at 98% reclamation... that ain't good.
    – Omegacron
    Commented Mar 8, 2017 at 21:16

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Unlike Galactica, many of the civilian ships were not equipped with effective water recycling system. Quote from your source:

Many of the ships like the Virgon Express were not made for long-term voyages - >and will have to tank off of us periodically.

This, possibly coupled with the sabotage disrupting (or stopping completely) the recycling process (see A J's answer) could lead to the depletion of the rest of the water supply in matter of weeks.

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    It just occurred to me that if the civvie ships weren't set up to recycle water, they probably weren't set up to store waste water either. Therefore, there would be a net loss to the water in the fleet even if Galactica herself was recycling 100% of water when she tops up the other ships and they dump the waste water out into space.
    – Darren
    Commented Mar 6, 2017 at 18:34
  • But in that case, they would only have had slightly more than twice as much time if the water tanks didn't blow, not years like stated in question?
    – Daniel Vestøl
    Commented Mar 6, 2017 at 18:55
  • @Darren, so then the civvie ships must have given their waste water back to Galactica. Otherwise, as you say, the water would all run out. (Reminds me of The Moon is a Harsh Mistress, which is an excellent read, by the way.)
    – Wildcard
    Commented Mar 7, 2017 at 0:58
  • @DanielVestøl I believe that the civilizan ships did have some recycling, just not nearly as close to 100% as the Galactica.
    – daboross
    Commented Mar 8, 2017 at 1:49
  • Besides, even the Fremen can't reclaim 100% of their water... and they wring out dead bodies.
    – Omegacron
    Commented Mar 8, 2017 at 21:19
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Why would a ship able to recycle all water consumed have trouble running out of water?

Well, it surely takes time to recycle the water. And you would need water for all necessities over that time. If you don't have enough water, how you are supposed to survive, given that water is the most important necessity for human and other living things.

Borrowed from the answer from other SE

With efficient recycling you can get by with a little more (there will always be some loss — and retention as well; quoting a different SF series, carbon-based life is "ugly bags of mostly water") than just enough water to keep people, animals, plants, etc. alive for several days; you need long enough for enough of the water consumed to get back into the ecosystem and be recycled. Lose enough water, though, and you could easily get into a situation where you don't have enough water for all necessities over the period needed for that water to get back through recycling — and water is more critical than food; you can if necessary go a week or so without food, but only a couple days without water. And many plants are more sensitive than humans.

(emphasis mine)

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  • It's closer to 3 weeks without food. 3 minutes without air, 3 days without water, 3 weeks without food. Assuming an environment close to comfortable (extreme temperatures, humidity/dryness, etc.) can affect these numbers (but usually not in a good way).
    – Jonathan Fite
    Commented Mar 6, 2017 at 16:20
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    As written, this assumes multiple things, incl. A) water recycling is a batch process, not a continuous process (any system for the Galactica itself would be a continuous process, with maybe some stages that have multiple batches running at a time), and B) the water in the tanks was needed to fill the use➞recycling pipeline. The situation described, the system was already in operation with the entire cycle already full of water in all stages. While what is described may have been issues, without more explanation (e.g. that recycling for other ships is batched) this supposition is incomplete.
    – Makyen
    Commented Mar 6, 2017 at 17:17
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If we recycle all water in a self-sustainable way, and lose 60% of our water, the only way our loss is sustainable is if our initial water utilization was only 40% or less.

That is, we're in big trouble unless our ship was carrying 250% of its peak water demand.

This seems inefficient. If we can carry that much water, why worry about recycling so efficiently that we waste "not a drop"?

But if our water supplies are any less, then after losing 60%, we don't have enough to match peak demand: we'll need to ration, to lower that peak.

This will be uncomfortable, and there will be certain maintenance operations which cannot be rationed away: merely postponed. The food supply will suffer if irrigation is reduced for too long; sanitation will suffer if water for cleaning the ship is reduced too long; morale will deteriorate rapidly; etc.

How quickly this all becomes an issue, and how urgent that issue is, depends on lots of factors. But in the absence of life-threatening risk, it would certainly be the highest-priority issue on the ship.

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  • Except, based on the question, they were able to retain 100%... so this doesn't apply in this case.
    – Catija
    Commented Mar 6, 2017 at 23:02
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    @Catija It has nothing to do with retention. Think about it this way. They have a pitcher full of water. It holds enough water to fill 100 cups. They loose 60% so now they can only fill 40 cups. They still have 100 cups that need water, so they are going to run out of water before they fill all the cups. It doesn't mater that after the cups are full they are going to recycle the water back into the pitcher, because they can't fill the cups in the first place.
    – stonemetal
    Commented Mar 7, 2017 at 6:53
  • That's a really clear and concise way of explaining it, @stonemetal :) And then we can go into more detail and saying "by rationing, they can probably get by for a while with only 40 cups being full at once, but at some point, even with rationing, they're gonna need to use at least 50 cups at once, and then they're in trouble."
    – Dewi Morgan
    Commented Mar 7, 2017 at 20:49
  • @stonemetal The cup isn't [half] full or empty, it's the wrong size... Water isn't a discrete unit. Multiple references were made to rationing (shrinking the size of the cups). Plus, usage would be spread out over time. It seems to be more of a peak flow issue. Think of it this way... The Tank is a buffer (or battery if you prefer electronics) As water is used, it empties. As it's recycled, it fills. Thus it can handle peak demand greater than the recycling rate for short periods. The larger the tank, the longer the system can provide water at peak times. It has to be topping off other ships.
    – Basic
    Commented Mar 8, 2017 at 22:28
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Previous answers are spot-on, but there are other (perhaps even major) points of water loss that each overlooks that would cause loss even in a system with 100% recycling efficiency:

  • People transferring from ship to ship. If an individual comes from another ship in the fleet and eats and/or drinks while aboard the Galactica, then departs, the quantity of water they've consumed is a net loss to the Galactica's reserves. While individually small, these losses would tend to accumulate over time, although they would be partially offset by people boarding the Galactica (perhaps even enough to roughly balance).

  • Atmospheric loss. There is a large volume of air aboard Galactica, which contains water vapor. As air is lost, some of this water vapor is also lost and will be replaced through evaporation.

  • Open-ended chemical processes. Human consumption is not the only drain on water; water is likely also used for other purposes, some of which may be open-ended (non-recycling).

  • Food export. Galactica is shown during the series to be a major source of food, etc. for other ships in the fleet. Assuming that at least some of this is produced aboard Galactica (and not just prepackaged provisions), this would be a steady drain on her water resources.

  • Absorption of atmospheric moisture. Many materials are hygroscopic, that is, they absorb moisture from the atmosphere, which is a net loss to the overall water supply. - Credit to @Tonny, who noted this in the comments.

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    I like your point about open ended chemical processes. Maybe they use the hydrogen as fuel for something?
    – Daniel Vestøl
    Commented Mar 6, 2017 at 21:15
  • That occurred to me as well, but as a separate item; I wasn't thinking of that as a chemical process :-). I was thinking more of manufacturing/synthesis processes.
    – Deacon
    Commented Mar 6, 2017 at 21:28
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    And don't forget that many materials are to some extend hygroscopic. They attract/absorb water (from the air). That water is a loss from the water-cycle/re-cycling.
    – Tonny
    Commented Mar 9, 2017 at 9:00
  • Good point, @Tonny. I've added it to my answer, with attribution.
    – Deacon
    Commented Mar 13, 2017 at 13:01

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