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?