Answer:
The man who invented it doesn't want it. The man who bought it doesn't need it. The man who needs it doesn't know it. What is it?
It's like food but water kills it. What is it?
Round as an apple, deep as a cup, and all the kings' horses can't fill it up. What is it?
When the son of the water returns to the parent, it dies. What is it?
I run around the city, but I never move.
I repeat only the last word you say. The more I repeat, the softer I got. I cannot be seen but can be heard. What am I?