Water as allowed to fall on a turbine fixed with a bar. Due
to the movement of the turbine, the bar also moves, and this
energy is converted into electricity.

1)Most hydroelectric power comes from the potential energy 
of dammed water driving a water turbine and generator. In 
this case the energy extracted from the water depends on 
the volume and on the difference in height between the 
source and the water's outflow. This height difference is 
called the head. The amount of potential energy in water is 
proportional to the head. To obtain very high head, water 
for a hydraulic turbine may be run through a large pipe 
called a penstock.
2)Waterwheel (Horizontal wheel)
The wheel is usually mounted inside the mill building below 
the working floor. A jet of water is directed on to the 
paddles of the water wheel, causing them to turn. This is a 
simple system, usually used without gearing so that the 
axle of the waterwheel become the spindle of the mill. This 
system is sometimes called the Norse mill. In a sense it is 
the ancestor of the modern turbine