The picture illustrates the process of electricity manufacture in a hydroelectric power station.
It is clear that the process involves various stages beginning with water flow in high-level reservoir and ending with electricity in power lines to the national grid.
Looking at first step of the process, river water stored in high-level reservoir which is blocked by a dam. Following this, an intake at the bottom of this dam which is opened in day to allows the flow of water to generate electricity and closed at night to the water flows out into the river below the dam during pumping.
In day, water flow to generating electricity by an operate generator in a power station then it is moved in power lines to national grid. By contrast, water from low-level reservoir will be pumped into high-level reservoir during the night to ready for day time activities.