Steam venting seems out of place in a high-tech setting, but in actual fact the most advanced modern naval vessels are driven by steam; they may use nuclear fission instead of coal or oil as the heat source, but the rest of the plant uses the same basic physical principles that drove the industrial revolution. Even the most advanced real-world theoretical engine designs are built around liquid or gaseous reaction mass (in the form of hydrogen, oxygen or water) for propulsion. Despite this, steam does not regularly vent into engineering spaces, which is good, because getting hit by a jet of steam at 600-1250 PSI and 400 deg F would ruin your entire day. And by ruin your day, we mean flash bake you and rip you into pieces. Also note that in marine steam engines, the gas doing the pushing does not normally get vented during operation. The water is boiled, the steam spins the turbines, and then cools and condenses back into the boiler. If the working fluid escapes, that is a problem with the engine, not normal operation. Locomotives and some land-based steam engines do vent the steam, but they can top off their water tanks whenever they need to. Although ships float in the ocean, which is an essentially infinite source of water, the salt and other impurities must be removed from the water before it can be used to make steam. Failure to do so leads to very rapid corrosion of the whole steam system and will eventually introduce the crew to the horrors of the aforementioned steam line rupture. Distilling water is a space-consuming and energy-intensive operation, so even in old-school reciprocating steam engines (which resemble a steam locomotive's engine, being piston driven vice turbine driven), it was still much more efficient and safe to re-use the fresh water you already had, vice venting it and constantly having to make more. Many real rockets using cryogenic (really really cold) fuels have water vapour condensing around their tanks, just like you can breathe out white clouds on a cold and dry day. You can also sometimes get this effect from a large refrigerator or freezer. Note, though, that this happens only because the atmosphere we see them in (Earth) has water vapour; you should not see this happening on asteroids, in space, on the Moon, etc. Unless space life-support is meant to replicate earth atmosphere (would make sense, considering pure oxygen is quite flammable - which complicates things like hot steam engines).