Eight billion

"... Women in Africa — and the job falls to women — must spend six, eight hours a day just in trying to bring clean water to their children.

Eight billion hours a year of human effort are spent just in bringing water. And when I heard that statistic, sitting like you are in an audience, I thought, 'Well, he must have said eight million.' Then I thought, 'Maybe it's 80 million.' It's eight billion hours a year of wasted effort because the water is often contaminated when it gets there. This isn't rocket science. You can fix this."

Quote from a commencement speech by Anthony M. Kennedy, Supreme Court justice, at New York University, as quoted in the New York Times.