Back to the Future

"Mother, what is water?" asked the baby fish of the mother fish.
"Water is what you swim in. Water is what you're mostly made of." 
"But where is it?"
"All around you." 
"But I can't see it," said the baby.
"Of course you can."
"Where?"
"Everywhere."
"And I'm made of water?"
"Mostly." 
"And after I die..?"
"You go back to being water," said the mother.