Here you go, part 3 of the Steam's Limitations series (read part 1 and part 2 here). In this installment, we'll be talking about water supply -- probably the most important limitation for steam technology besides having enough fuel.
You cannot, I repeat, cannot run a steam engine without water. The very name of the technology means you need to change water from its liquid form into steam, its gas form, which will then make the mechanical innards of your machine speed along. Burning your fuel does nothing except create the fire that boils the water that runs the steam engine.
Because of this need for water, it stands to reason that you'd have to supply your steam engine with a constant amount of the live-giving liquid in order to ensure its continued operation. Whether this is through a water tank on the vehicle, a pump that pulls the water from the ocean, or someone whose sole job it is to spray water into the boiler, it just has to be there.
What's this mean for your steam-powered mechanisms?
Sufficient water supply, like sufficient fuel, is a requirement for your steam machine to keep going. This is regardless of the size of the machine, or of the engine. However, as we saw in part 2, larger steam machines require bigger amounts. So our aerial steam vessel would need to either find a way to draw water vapor from the air/clouds or carry a water tank on board that grows larger as the airship increases in size. Which, depending on weight, can make it that much harder for your flying machine to stay airborne.
This is one of those cases where oceangoing vessels come out ahead. They can draw their water supply from the medium they travel in very easily. Look at the steamboats that plied the Mississippi River in the 1800s. They used water wheels to supply a steady flow of water to the boiler, which would create the steam that drove the engine. Any naval vessel can do this -- water wheel not required.
And now we bring this series on steam's limitations to a close. I hope you learned something about what to consider when building a steam machine.
P.S. As always, adding magic into the equation can possibly eliminate real-world concerns. Author's prerogative of course.
P.P.S. Brownie points to the person who guesses which songs I took this post's title and part 2's post title from.