By Deborah Grau

In 2007 he was named People magazine's Sexiest Man Alive, but these days, Matt Damon is getting noticed for something far less sexy. "Probably the least sexy thing is water," says Damon. "But, you know, it's a huge issue for women and girls, and they're the ones affected the most. And, as a father of four girls, I feel it personally."

Damon learned the severity of the problem during a trip to Africa in 2006. When he returned home, he made it his mission to help people in developing countries have access to safe water and sanitation. "You will never solve poverty without solving water and sanitation. It cannot be done," says Damon. He partnered up with Gary White, an engineer and water specialist, to form the nonprofit organization Water.org in 2009.

The scope of the problem is devastating: 748 million people lack access to clean water, and every minute at least one child dies from a water-related illness such as diarrhea, which kills more children than malaria, AIDS and measles combined. Women, who bear the primary responsibility for water collection, spend a combined 182 million hours a day collecting water.

"If there's not a water source nearby, they scavenge all day until they find water for the family," says Damon. "In these urban and peri-urban areas, a lot of people have had jobs that they were taking time away from to go collect water. And so Gary — this idea basically was to buy them their time back. Connect them to the existing infrastructure."

White's idea is called WaterCredit, which provides affordable loans for water and sanitation improvements. The loan is about $200, which provides for such basics as a water connection and a toilet. It takes a couple of years to pay back the loan, but the impact is incalculable.

"It's giving people back their time," says White. "They go out and work at a paying job now. Or they can show up at work on time because they're not scavenging for water and, you know, seeing kids in school now because of the fact that they're not carrying water."

So far more than 370,000 loans have been given out, affecting more than 1.6 million people. However, White says, "We don't pretend that it's gonna work for everyone. But it has worked for people living on as little as $1.25 a day. But if we can find that segment of the market that is so poor that this doesn't work for, the good news is the subsidies and the charity that we save from the people who can take water credit can then be redirected to those in absolute poverty and help them get access."

Who do you think is a global game changer, and what person would you like to see featured in this series? Let me know on Twitter (@katiecouric) or Tumblr.