The diagram illustrates a natural process known as the water cycle in
which water passes from ocean to air to land.
Overall, what can be seen from the picture is that the phenomenon
contains three main stages, beginning with the ocean water being evaporated,
falling as rain, and ending with water running back to the ocean.
Starting at the evaporation stage, it is clear that 80% of total water
vapour in the air comes from the ocean. Once the water has been evaporated
by heat from the sun, clouds are formed from water vapour. Following this,
after having the right conditions, clouds fall as rain or snow.
At the last stage of the cycle, rainwater may take various paths. Some
may fall into lakes or small ponds, while some return to the ocean via "surface
runoff". Otherwise, rainwater may be absorbed through the ground to the
impervious layer of the Earth. Saltwater intrusion is shown to take place
before groundwater passes to the ocean to complete the cycle.