I'm not going to write your speech for you but I will give you some points you can put in.
1. Water is necessary for all life.
2. Water is a natural building block for most elemental bonds.
3. Water is needed for cities, such as the disposing of waste and adding a warm vista like Venice.
4. Water could push a civilization into an empire.
5. Without water the Earth would be uninhabitable.
You can go into further detail about these points and explore them more, or you can make new points as well.
