This question may be a bit silly, but this video of Chris Hadfield wringing out a wet washcloth on the ISS got me thinking...

In the video you can clearly see drops of water floating away from the cloth, and as I understand it, they'll be sucked into the ventilation system and recombined with the astronauts' water supply.

So how much water could be in the 'internal atmosphere' of the ISS (or any spacecraft) before problems start arising? Suppose some water tank burst and now X percent of the ISS volume is filled with water. What is a dangerous X and how would the water be dealt with?

Surely a lot of water floating around would get into instruments and damage important circuitry. Could the ventilation systems handle it? Would the surface tension of water be a blessing or a curse? Is the thought of having astronauts 'swim' through the ISS in search of air pockets pure science fiction?

  • $\begingroup$ Even if an astronaut found an air pocket, how would they clear the water from their face to breathe without something to absorb the moisture? $\endgroup$
    – Ellesedil
    Sep 23, 2014 at 17:13
  • $\begingroup$ On seeing the answers so far it might be that you'd like to re-phrase the question/title so that it addresses a more plausible risk. i.e. a water container leaks into a small enclosed space which, perhaps, governs access to some sensitive equipment. This way you'd hopefully get the questions of your third and fourth paragraphs addressed. $\endgroup$
    – Puffin
    Feb 18, 2022 at 23:44
  • $\begingroup$ @Ellesedil this is an interesting idea too. However see my comment above, your additional question probably won't be addressed either for the same reasons. Perhaps a practical example of a risk would be if a crew member had to access an enclosed space so as to deal with the leak. You could re-write this as a new question if Calvin's Hobbies doesn't incorporate it in their question. $\endgroup$
    – Puffin
    Feb 18, 2022 at 23:48

3 Answers 3


The ISS Emergency Procedures book (alas, only 2000 edition (configuration 5A) is publicly available) lists the following contingency:


If Contingency Water Container fill not in progress Then
    Perform H2O Vent
    If Condensate Qty not decreasing Then 
    End If
    If Contingency Water Container fill in progress, contact MCC-H
End If
  • $\begingroup$ Interesting, but cryptic. Incidentally, why does the check- mark or square-root symbol mean "contact"? $\endgroup$ Sep 24, 2014 at 11:23
  • $\begingroup$ @Calvin'sHobbies maybe (my speculation) check-mark -> "(cross-)check with" -> contact $\endgroup$
    – Federico
    Sep 24, 2014 at 13:38

Water doesn't compress, so in order to have the ISS fill up with water you would need a water tank with the same internal volume of the ISS to contain it. You would then need to spend an awful lot of energy to lift that much water (that's a lot of water, and a lot of weight) to orbit. This clearly hasn't happened.

Say you did have that much water, you'd have significant technical challenges actually filling the ISS up with it as you'd have to work out how to move the displaced oxygen out of the way for the water to replace it. It wouldn't happen by accident. What would happen is you'd have a leak and the astronauts would shut down the water supply until they found and repaired it.

So it's just not going to happen.


There isn't enough water on the ISS to create the scenario you describe in your last sentence. A rapid leak would still be a serious problem, for the reasons you mention of electrical shorts and associated galvanic corrosion.

The designers probably keep tank pressures somewhat low and pipe diameters small to reduce the likelihood of a rapid leak (e.g. in the event of a failed valve).

  • $\begingroup$ Water doesn't compress, so how could you have a high-pressure water tank? $\endgroup$
    – GdD
    Sep 24, 2014 at 12:31
  • 1
    $\begingroup$ @GdD See here and here $\endgroup$
    – called2voyage
    Sep 24, 2014 at 13:38
  • 2
    $\begingroup$ Density != pressure $\endgroup$ Sep 25, 2014 at 5:47
  • $\begingroup$ Water does compress, it just takes a lot of pressure to make it do so, A high pressure water tank only needs a tiny change of volume to be a very high pressure water tank. $\endgroup$
    – DJ319
    Feb 6, 2019 at 14:06

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