Maybe some of this has already been gone over and I've missed it, but here's a suggestion. Perhaps boilers could be used as an alternative to windmill and waterwheel power sources. Water could be routed or pumped to a boiler which can be used to run other pumps. The boiler could be situated over magma or fueled like a furnace to boil water. The steam pressure can power nearby pumps or be piped to relatively close pumps.
The output steam would either need to be piped out of the fortress, or to a reservoir room to condense and possibly be directed back into the boiler for reuse. A spin-off from this idea would be that the evaporated water would become desalinated when it is re-condensed. This is a bit more simple than real-life desalinization, but still a bit more accurate than having a screw pump desalinate water.
A player would have to ensure that the boiler's output energy would be enough to compensate for the fuel used and any pumps used to bring water to the boiler. On this logic, a player could do something completely pointless such as making a boiler that powers only the pumps it uses to bring its own output water back to it.
Boilers could also be used to transport water by means of pressurized steam through pipes. Players would have to ensure that the boiler produces enough pressure to push the vapor to its destination, or at least to a point where gravity can take it to its destination.
Pressurized, hot steam could also be a hazard for dwarves. Having a dwarf deconstruct a pipeline from an active boiler could flood the room with searing hot steam scalding nearby dwarves to death and causing a mess of water afterwords.
It seemed like a
fun idea to me, although I could see how it would be difficult to code and provide more complications to gameplay.