The heat comes from the power supplied - as flow rate times the pressure drop. You'd get virtually no heat from it.
Further, you'd get the SAME heat whether you "spin a fan" or just let the incoming water lose some of its pressure through turbulence. So why add a moving part (and trouble) for no gain?
The heat in the Finsawyer system comes from the power used to spin the fan against the water's friction. You can shape your fan to generate a LOT of water friction - and consume a lot of power - to "waste" that power by turning it into a lot of heat.