Over the years and various interpretations of Superman, his physical needs have varied greatly. Sometimes he never needs to; other times he has more endurance than a human, but still needs some food and water. Depends more on the writer and the time period you're talking about. That's not counting, of course, the variations in the comic/TV/cartoon/movie versions.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort