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Actor Matt Damon has been a genius from Southie in "Good Will Hunting," an assassin with amnesia and a brand-new conscience in "The Bourne Trilogy," and a contemptibly crooked cop in "The Departed."
But to hear Damon tell it, his most compelling role is bringing water and toilets to impoverished villages in developing nations.
"It's not just to improve their lives but to save them," Damon said in an interview with CNN's "The Lead with Jake Tapper."
It's particularly crucial for the young; water and sanitation issues kill children at a rate equivalent to a jumbo jet crashing every four hours.
Damon attaching himself to, and talking about an issue prompts people to pay attention to a topic that would otherwise go noticed.
"That's the hope. I mean that's obviously the small part I bring to Gary's just incredible expertise," said Damon.
Damon is the co-founder of water.org, his partner Gary White is one of the world's foremost experts in the field.
"We could reach more people with water and sanitation than if we just operated alone," joked White.
"Well I mean, I was really looking for the expert in the space, and when I couldn't get that guy," Damon says with a laugh.
But in all seriousness, "we complement each other and we, you know, Matt certainly has come a long way in water, not much for me in acting," said White.
Damon has lent his time and money to organizations that work to end AIDS, hunger, poverty and even junk mail.
But "this is the one that I spend all of my time on," said Damon. "I just was shocked by how massive water was. Water and sanitation. Water really, it kind of underpins everything."
Worldwide, more than 750 million people live without potable water, making them susceptible to disease. Since 2009, water.org has helped communities connect to clean water supplies through wells and micro loans. The founders say their approach isn't just charity, but a sustainable solution, offering programs like water credit.
"Basically, right now people are getting access to water in whatever way they can. So if you're in a slum in India, you might be spending hours every day walking to a public tap, waiting in line. Water's sometimes there, sometimes not. You might be paying the water mafia, which is basically people who come around and sell you 20 liters of water for a pretty high price," said White.
"If you could actually just front them the money to connect to the municipality that was piping water right underneath their feet ... you'd give them their time back, so they could work at their job and and pay the loan off," said Damon.
CNN traveled with Damon and White to India, where they checked in to see how their water credit loans are working.
"When Matt and I were in India, we met a woman who was paying 40 rupees every day for her family to go use the public toilet," said White. "So with her in her situation, she was able to get a water credit loan, that ... allowed her to build a toilet in her home."
Her loan payment is 40 rupees per month, which she will pay off over two years. She will then have to pay a small fee as a water customer each month, but "she'll come out way ahead," said White.
Damon's friends and fellow actors George Clooney has projects in Sudan, and Ben Affleck concentrates his efforts on the Eastern Congo.
"There was never like a meeting or anything, or a 'You take this and I'll take that.' I think it was, I think there are a lot of us who think similarly about these issues, and just connected personally to different ones," said Damon.
Damon found a cause that may appear to be the least sexiest one an A-list actor could attach himself to, but he said the goals of the organization have a huge impact, and are achievable.
"It is the most impactful issue, and I think the other thing that most disturbed me about it is, it's so preventable," said Damon.
More than one billion world citizens still practice open defecation due to lack of sanitary facilities, and the resulting disease kills millions each year. It is not a glamorous topic to discuss at Hollywood fundraisers, but Damon hasn't shied away.
Earlier this year he launched a spoof campaign with fellow celebrities to bring attention to preventable disease and sanitation issues.
"Until everybody has access to clean water and sanitation, I will not go to the bathroom," the actor dead pans in the first campaign video.
"When we would speak about this issue ... it would go up on YouTube, and it would get like three hits, and that was after me and Gary watched it," Damon said, with a laugh.
"So we went, okay some of this isn't really working, whereas some of the viral stuff I've done gets millions of hits," said Damon. "If you can get somebody to laugh about something ... and you can entertain them, but they can start to kind of dive down a bit on the complexity of this issue, then we're really getting something done."
Damon is big on getting things done. In 2011, the activist made political headlines when he told Elle magazine he was disappointed with President Barack Obama, saying he preferred a "president with some balls who actually got stuff done."
The comment did not go unnoticed.
"Matt Damon said he was disappointed in my performance. Well Matt, I saw "The Adjustment Bureau," right back at cha," Obama joked at the White House Correspondents Dinner in 2011.
"He got me good," said Damon.
While his fame brings needed attention to Damon's causes, that spotlight highlights his comments for naysayers as well
"I've kind of chosen my words poorly when talking about him," said Damon. "The truth is I voted for him twice, I campaigned for him, and it's humbling to think about that job and how hard it is. Particularly in the headwinds that he faces, the kind of historic headwinds that he's facing. And I have a massive amount of respect for him and ... I really wish him well, particularly right now."
Damon takes the criticism in stride.
"If you put a megaphone out and say something, then it's within any American's right to say something back to you," said Damon. "When I speak out about something like public education, I mean it really means a lot to me."
"But it's also why I'm particularly happy why I spend all my free time working with water.org," said Damon. "One of the things I love about it so much is its totally nonpartisan."