"Wherever we've travelled in this great land of ours, we've found that people everywhere are about 90% water"

In this quote, David Letterman is highlighting the fact that no matter where we go in the United States, we are all basically the same. He utilizes the metaphor of water to represent the commonness amongst individuals. Just as water is vital for life, our shared humankind is what links us all. Letterman's usage of the phrase "excellent land of ours" also recommends a sense of pride and unity in being American. In spite of our distinctions in culture, beliefs, and backgrounds, we are all made up of mostly water, emphasizing the concept that we are more alike than we are different.