IELTS - task1: Ocean Thermal Energy Conversion !!!

The diagram below describes the process including four main stages of producing electricity by a system called Ocean Thermal Energy Conversion (OTEC), which is based on the changes of seawater temperatures in different depths.

Firstly, warm seawater that flows into the pipe of OTEC on the surface is heated to convert into water vapor by solar energy. In the second stage, in the evaporation chamber, saltless water vapor is evacuated to turn turbine creating electricity. In the next step, water vapor goes down to the condensing chamber, becoming drinking water. Paralleling to these stages, salt is separated in the process of evaporating warm seawater moves to deeper levels of seawater, dissolving in cold seawater which is discharged from this system as waste salt water and this process can be repeated.

TOEFL listening lectures: The professor mentions watermelons as an example of what?