Why have you chosen to focus on water in your philanthropy?
I met the engineer Gary White, and I was so inspired by his innovations that we founded Water.org He invented WaterCredit, which takes the concepts behind microfinance and applies them to water. Say you live in a slum in India, where a municipality is piping clean water through the neighborhood. For a $75 loan, you can get that water coming directly into your home forever.
At the Save Our Schools rally in Washington, you made comments defending teachers that received a lot of attention.
My mother is a professor of early-childhood education. At the rally, I just wanted to boost teachers' morale because they've been taking a real beating. How many young people are not going into teaching who would have if there was more prestige or if public treatment of teachers was better?
You've been critical of President Obama recently. What kind of leader do we need?
Somebody who believes that building a strong, solid, educated middle class is ultimately the best thing for America. Someone like FDR. There's a misconception that leaders lead. They don't. They follow. Every great movement has come from the bottom up.