I recently started watching the TV series "The Expanse", which is based on a series of books (I haven't read). The central premise of the show is that water is a scarce commodity. The Ceres settlement is in fact dependent on shipments of ice harvested in Saturn's rings.

This strikes me as rather odd. Building a closed system which does not waste water at all would seem comparatively easy to me. That would basically solve the entire problem in one swoop.

Building a closed water system would - by my guess - be easier than any of:

  • Growing trees on an asteroid
  • Building space ships that don't leak any significant amount of air
  • Reaching escape velocity regularly
  • Building any type of settlement on Mars
  • Space warfare

Does the series (either the books or the TV show) offer an explanation why water is such a rare commodity?

  • 7
    The population of the Belt is continuously growing, so even if they developed a perfectly closed environment, they would need new water stocks anyway.
    – user54256
    Commented Dec 23, 2015 at 20:00
  • 10
    There are no closed systems. We live in a universe where entropy, and hence, wastage, always happens. You will always, eventually, lose water, through leaks, through filtration system inefficiencies, etc. Also, water has mass, like anything else. Populating a space (like an asteroid) that doesn't have any to start with means bringing it with you. That's expensive. Commented Dec 23, 2015 at 20:23
  • 1
    Example from a different universe: in Dune, it's said that a properly maintained and used stillsuit can keep a person's water loss down to less than a thimble-full per se. Well enough, in an environment where moisture is scarce, but still extant and harnessable, and hence, one can eventually replenish what one's lost. The loss of a thimble-full per day FOR ANY REASON in any of the colonial environments in The Expanse would ultimately mean death for everyone involved unless it were replaced from outside sources. Commented Dec 23, 2015 at 20:29
  • 1
    @UncleMikey Earth is pretty close to a closed system (when it comes to water). Also, Ceres supposedly started off covered in ice, which we strip mined before populating it. This 'verse is making less and less sense to me (there also seems to be a miscalculation regarding gravity). As for Dune, interesting comparison. Somehow Dune never triggered the same question for me. Of course the "lost water" stays in the system "Arrakis" and living in artificial domes on Ceres makes quite a difference. And rationing shower water (which shouldn't get lost on Ceres) seems sort of pointless to me.
    – Jasper
    Commented Dec 23, 2015 at 21:05
  • 4
    Water might not be scarce, it might be cheaper to ship in (relatively) clean water ice than process it for re-use on station. Remember that in most situations here on Earth, our water reuse cycle includes a full evaporation-precipitation cycle (we treat sewage and discharge treated water into waterways, and capture rainfall into reservoirs). Its the same situation as throwing something away and buying new rather than repair and reuse - we are only just getting into recycling now.
    – Moo
    Commented Mar 15, 2016 at 10:18

7 Answers 7


Having not seen the TV show, I can only relay what was in the show's source novel; Leviathan Wakes


If you asked OPA recruiters when they were drunk and feeling expansive, they might say there were a hundred million in the Belt. Ask an inner planet census taker, it was nearer to fifty million. Any way you looked, the population was huge and needed a lot of water.

The shortage is largely artificial

“A water hauler millions of klicks from here got vaporized. Why are we going to full alert? Our cisterns will last months without even going on rationing. There are a lot of other haulers out there. Why is this a crisis?”

The water shortage is a natural result of inter-planetary tension

The Martian navy had suffered a series of harassing attacks by Belters. A half ton of super-accelerated gravel had forced two of their battleships to change course. A slowdown in water harvesting on Saturn’s rings was either an illegal work stoppage, and therefore treasonous, or the natural response to increased security needs. Two Earth-owned mining operations had been attacked by either Mars or the OPA. Four hundred people were dead. Earth’s blockade of Mars was entering its third month. A coalition of scientists and terraforming specialists were screaming that the cascading processes were in danger, and that while the war would be over in a year or two, the loss of supplies would set the terraforming effort back generations. Everyone blamed everyone else for Eros. Thoth station didn’t exist.

On top of that, we see numerous instances of the water being used for other stuff that takes priority over the individual need of low-value colonists and workers:

  • Fuel (as reaction mass)
  • For more critical life-support purposes (turned into air)
  • Terraforming projects (Mars being greened)
  • Being wasted by rich people (on showers and the like)
  • Lost to faulty engineering (vented into space)
  • Clarified: I'm definitely looking for book-based answers as well (and in fact, I think that the TV series is too young at the moment to have an answer - if it's ever going to have one)
    – Jasper
    Commented Dec 23, 2015 at 23:03
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    @Jasper - If I were you, I would definitely hang fire on accepting this (or any other) answer until you've had some more responses, especially from someone who's actually seen the show.
    – Valorum
    Commented Dec 23, 2015 at 23:27
  • I find it odd that water would be so scarce. It is the second most abundant compound in the universe after H2. Hydrogen is the most abundant element, and Oxygen is third, so just combine them and get the second most abundant compound. The outer solar system has entire moons made mostly of water ice, and we astronomers think there is plenty of water trapped deep inside the Trojan asteroids. Then again, if you split the water into Hydrogen and Oxygen, and burn that H2 as fuel in a thousand rockets every day ... Oh ... nevermind.
    – RichS
    Commented Aug 8, 2017 at 5:35
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    TL;DR: The reasons are largely based on the same kind of power politics and financial speculation that we have now on Earth over oil and food: we haven't experienced a critical global shortage of either in a long time but (expected) supply fluctuations and distribution issues (all often due to armed conflicts) coupled with upwards of a billion people who already spend the majority of their income on potable water, food, and heat exacerbate the problem. Commented May 22, 2018 at 20:39
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    @DavidFoerster - As I've pointed out on several occasions, the reason why there are shortages of food isn't because there isn't enough food, it's because there's a shortage of good governance.
    – Valorum
    Commented May 22, 2018 at 20:58

From a purely "realistic" stand point, water is the least rare thing in the Belt. There are plenty of asteroids with billions of liters of water, there are dwarf planets spewing out into space. Also that means if there is water, there is O2, lots of O2. Making water and air an issue in the show and books, shows no research AT ALL was done on this topic. Having to travel to Saturn for Water....sigh. It's easy enough to come up with things that could be commodities in a space story. Water and Air and not them.

  • I believe this was mostly looking for an in-universe answer, but as it's not specified this answer seems valid. Although you make some bold claims, any evidence you can show that the show did in fact do no research?
    – Edlothiad
    Commented Aug 8, 2017 at 7:35

I like Richard's answer very much, and having read the books and now watching the series (I would like it better if I never read the books, but still, it's space SciFi on TV!), I would venture that production of oxygen (Richard's 2nd subset point) is the main and most important use of water in a space colony. Either directly broken down into hydrogen and oxygen or via plants. You can live a few days without water but only a minute or so without air.

In fact, this is brought up as one of the main differences between a Belter and an Earther - the ability to go outside and breathe.

I don't recall other ways that they obtained breathable air, but sometimes I don't read for comprehension as much as for entertainment.

  • This could be, but it would still not make much sense. E.g. on ISS they are actually using water to create oxygen, but given the advances of the civilizations in the Expanse, there really is no reason to not get the oxygen back from the carbon dioxide emitted by breathing humans, especially considering that we already have this technology.
    – a20
    Commented May 23, 2018 at 20:45
  • sciencealert.com/… - low cost does not mean simple. Presumably in a few hundred years this would be an effective and viable solution. But I'm betting that a space based society will still be using electrolysis to convert water to oxygen if only to supply losses or when fancy conversion tech fails. I can imagine in-verse, CO2 conversion equipment are all built and supplied by Earth or Mars based companies. Hard to know, SciFi has that Fi aspect to it. :)
    – Jim
    Commented May 24, 2018 at 14:28
  • Oxygen as a gas will be harder to contain. It might be leakage of oxygen, and deliberate loss of hydrogen as fusion fuel that they are replacing.
    – craq
    Commented Apr 9, 2019 at 18:56

Right at the start of the first episode the voiceover mentions that Ceres used to be covered in ice, but it was mined and removed (by Earth or Mars, I can't remember which, perhaps both) and this has resulted in Ceres having to import water (in the form of ice). This issue is also mentioned by the street preacher later in the same episode. Since Ceres by this time has a population in the millions, water has become a scarce resource.

Even with grey water recycling, there will never be a completely closed system and new water supplies will always be required to sustain the population.

  • 2
    Wasn't that voiceover the same preacher before we got to see it was him? I think during his speech the "camera" moved through the station and finally ended up at the preacher.
    – Jasper
    Commented Jan 13, 2016 at 11:10
  • @Jasper - The text blurb at the start of the show should have said, "The inner planets depend on the resources [provided by people who live in] the asteroid belt [but are acquired elsewhere, as the resources of the belt have been exhausted]."
    – Mazura
    Commented May 13, 2016 at 14:42
  • @Mazura No. It could have said "the inner planets depend on the resources from the belt and the belt depends on resources from yet elsewhere", but they decided to leave the last part out (which is a perfectly valid choice. That said, I'm done with this discussion and will remove my share in it, as it is of no added value for the future.
    – Jasper
    Commented May 14, 2016 at 13:34
  • This is complete BS. It is estimated that up to 30 % of the mass of Ceres comes from water. In the series they have certainly not mined away 30 % of the mass of Ceres. This would correspond to roughly 3*10^20 kg. On Earth, there is about 1.4*10^21 kg of water, so what this preacher is claiming is that water corresponding to 20 % of all the water on earth has been mined away... Now, these are estimates with uncertainties, but the orders of magnitude simply don't make sense. This preacher was just part of the establishment, trying to scare people.
    – a20
    Commented May 23, 2018 at 20:41
  • @bjorn What are you trying to say? My answer is BS or the preachers's claim of water being mined away was BS? I think you mean the second one, but I can't see anything in your comment that supports this - the fact that water on Ceres is in short supply and has to be imported is a given, it's literally one of the key motivators for the rebellious belters in the story. Whether or not that situation is feasible in relation to the real life amount of water on Ceres isn't really relevant to the story.
    – user22478
    Commented May 23, 2018 at 23:46

This has bothered me as well.

-So long as a population has unlimited power, which seems to be the case, there shouldn't be a problem with scrubbing air and reclaiming water.

The explanations offered seem like strained logic trying to force the world to work rather than deal with the actual problem.

The only idea which comes close to, um 'holding water' is that the owners of the mining operations are deliberately creating shortages in order to control their work force. -Except that isn't indicated in the show, (unless you use more strained fan-boy semantics), so I think the artificial lack explanation is altogether too generous. The real reason is that the author just designed his world poorly.

But hey, it's sci-fi entertainment. Every sci-fi show gets a free pass in one or two areas. With Star Trek, it was the god-mode transporter/replicator problem. With The Expanse, we just have to look the other way when it comes to water and air being scarce.

Fair enough. It's otherwise a beautifully made and engrossing series.

But yes, definitely yes. The water problem is definitely a gaping logic hole.

  • 2
    Could you focus on the explanation?
    – Adamant
    Commented Feb 1, 2017 at 5:41
  • If you're using water for propulsion or to fuel for your generators, reclaiming the water is unlikely to be feasible
    – Valorum
    Commented Feb 1, 2017 at 10:30
  • 1
    "So long as a population has unlimited power, which seems to be the case" - why you think so? Commented Jan 15, 2018 at 11:39
  • In Mobile Suit Gundam Crossbones, in which there is a Colony in Jupirer. Water is also a rare supply. Commented Sep 24, 2018 at 18:54

From scifiwatcher's answer:

The only idea which comes close to, um 'holding water' is that the owners of the mining operations are deliberately creating shortages in order to control their work force. -Except that isn't indicated in the show, (unless you use more strained fan-boy semantics)...

Actually it's quite clear on the show why there are shortages on Ceres.

06:00, during the gaunt Belter's speech:

Gaunt Belter: Every time we demand to be heard, they hold back our water, owkwa beltalowda, ration our air, ereluf beltalowda, until we crawl back into our holes, imbobo beltalowda, and do as we are told!

Anderson Dawes: We do not want to live under anyone's boot, Fred Johnson, asilik towchu! Even a friendly one, afraid that if we disobey, we will have our air cut off, our water rationed, be spaced, or be herded into chambers to be used like animals.

  • You seem to be contradicting yourself. Are they holding back water or not?
    – amflare
    Commented Mar 22, 2018 at 21:18
  • 06:00 of what? (presumably some specific episode?)
    – RDFozz
    Commented Mar 22, 2018 at 21:52

Water is plentiful in the solar system but not so in many places where the Belters live and work. It's expensive bringing water to these places, sometimes from across the solar system.

Water is primarily used for the reaction mass for Epstein drives, teakettle drives and maneuvering thrusters as well as for production of O2 on spacecraft. Ceres must have a lot of water loss, it certainly isn't a closed system though it may have been intended to be in the past.

Other valuable commodities found in the Belt and elsewhere are metals, silicon for ceramics and lithium, which is a major plot point in Book 4, Cibola Burn.

  • 30 % of the mass of Ceres comes from water. This is about 20 % of the amount of water present on Earth.
    – a20
    Commented May 23, 2018 at 20:48

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