The Diagram shows the process of water use for producing electrical power, We can see that the Water has a cycle where it evaporates because of the heat of the sun, in this case the water for this process comes from the sea.
This water evaporated becomes a cloud until the water comes off the cloud raining over the montains, what it causes rivers along the way, This water is stored within a reservoir because of a DAM taht contains all the water allowing the water comes off the DAM by a small dorr ehre is the valve open/close to let the water flow trhough a pipe that ends in a turbine generating revs on it and creating electricity.
This electricity flows trhough wires which is transportated to a Transformer station where this highs power is reduced into small powers so it can be supplied to the big cities like schools, hospitals, etc.