For a tower you may want to see if dfhack can change some of the tower to be indoors or have a higher temperature.
You can also turn temperature off while everything is thawed but then magama won't burn or melt things anymore.
The only problem here is indoors doesn't stop water from freezing. It is Above Ground/Underground Status.
Any space that has a roof above it is considered Indoors, but any space that has been exposed to the sky is considered Above Ground forever.
It looks like if we want water in the tower we need a magma bloodline. It might be worthwhile to devote a two z-levels (one for water, one for magma)
of the tower for this purpose. If the magma needs move and get up that high we will need power. But windmills will be hard to deal with in a fort that might
accidentally built something high above them (I'm pretty sure that windmills need to be considered Outside to work and an accidental roof could make that tile
Inside). Plus there's the danger of the machine freezing if too cold.
Waterwheels are also equally unlikely. Would it be against the general idea of the fort to construct a floating flow? That is a tank of water high up that has
perpetual flow. A perpetual flow requires water to flow off the map, by either getting absorbed by an aquifer or literally off the map. The game marks the water
as having permanent flow. Then you simply dam it up and leave it mostly filled (as 7/7 doesn't realize it is flowing). That seems a little undwarven and a bit cheap
though. Plus there is still the potential to freeze unless the water is the magma-heated water. Which means we'd still need power to get the magma up there.
Ah, this is interesting and fun. It's vertical thinking. I'm so used to thinking down and across; thinking upward is kind of fun.