In my current fortress I am building a huge magma pumping stack. To at least acknowledge the laws of physics I decided against building a set of Dwarven Water Reactors and opted for a system of waterwheels that uses two aquifers that are located in my hill on different levels. It starts at a double aquifer at Z+1 and Z 0:
Z+1:
WWWW
A7.W
A7.W
A7.W
A7.W
A7.W
WWWW
Z 0:
*---*
WWWWWWWWWWWWWWWWW|Wd
WA7FFGFFXF___.WW[|]_
WA7WWWWWWW___WWW_|__
WA7FFGFFXF___.WW[|]_
WA7WWWWWWW___WWW_|__
WA7FFGFFXF___.WW[|]_
WWWWWWWWWWWWWWWWWWWW
Z-1:
*
WWWWWWdWW|Wd
W_FF___.[|]_
WWWW___._|__
W_FF___.[|]_
WWWW___._|__
W_FF___.[|]_
WWWWWWWWWWWWW
Z-2:
WWWWWWdWWWWWWWWWWW
W777F777777D7777FA
WWWWWWWWWWWWWWWWWW
W777F777777D777FA
WWWWWWWWWWWWWWWWWWW
W777F777777D77777FA
WWWWWWWWWWWWWWWWWWW
W: Wall
A: Aquifer with fortifications
7: Floor with water
_: Dry floor
.: Open space
F: Fortifications
X: Closed floodgate
G: Wall grate
[|]: Running waterwheel, hanging over open space
|: Horizontal powered axle
-: Horizontal powered axle
d: Door
D: Lever operated closed door
*: Active gear assembly
The real implementation is much more extensive with a total of 30 waterwheels.
The pumping stack is connected to one of the gear assemblies. Once I checked it was working (at that moment I didn't realize that only 15 wheels were supplying power) I turned off the water stream by closing the floodgates at level Z 0. Right now there is no stream of water running (tiles are 1 water or dry) and the wheels are still running with 1500 power output. Although i am not really complaining, I am curious if anybody has experienced the same situation of running water wheels without running water.
So far I assume this is a result of the two aquifers that have an invisible "stream" running between them, but more experimentation might give more insight.