Matt Damon used his ice bucket challenge to highlight the scarcity of clean water in developing nations, throwing toilet - instead of tap - water over himself.
The actor, who co-founded Water.org, a not-for-profit organisation helping to provide safe water and sanitation to communities in Africa, Asia and Central America, said that the dare “posed kind of a problem for me”.
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The ice bucket challenge has seen thousands of people, including many high profile public figures, dousing themselves with freezing water in a viral challenge for charity before nominating others to do the same.
It has become unofficially associated with helping to combat motor neurone disease (such as with the ALS Association), though many people have also been doing the stunt for organisations of their choice including cancer ones.
In pictures: The famous do the ice bucket challenge
In pictures: The famous do the ice bucket challenge
1/16 Lady Gaga
Lady Gaga managed to keep an admirably straight face as she poured what looked like a solid silver bowl of cold water over herself
2/16 Homer Simpson
Fans were overjoyed when their favourite yellow cartoon character got involved in the campaign to raise money to help those suffering from ALS. As per usual with Homer Simpson, things escalated quickly
3/16 Reece Witherspoon
One of those who have arrived slightly late on the scene, actress Reece Witherspoon looks nervous but resolute as she has a bucket of ice-cold water chucked over her head
4/16 Lily Allen
Lily wore a bikini as she self-administered her bucket of icy water. She thanked Jess Glynne for the nomination, and passed the challenge onto Mark Ronson, Millie Mackintosh and rapper Giggs
5/16 Daisy Lowe
Celebrity ALS Ice Bucket Challenge videos seem to be coming in faster than we can watch them - model Daisy Lowe is one of the most recent to get involved. She was nominated by Sun journalist Dan Wooton, and passed it on to radio presenter Nick Grimshaw and Abbey Clancy
6/16 Bill Gates
One of the first to go viral on YouTube, Bill Gates had freezing water tipped over him in a bid to raise millions of dollars to fight the illness ALS
7/16 George W. Bush
It felt like quite an important moment when the former President of the United States accepted nominations from his daughter Jenna Bush Hager, golfing champion Rory McIlroy, Woody Johnson, and Jim Harbaugh. He nominated 'my friend Bill Clinton'
8/16 Jimmy Fallon
In an official letter this week, the ALS Association said: 'Never before have been in a better position to fuel our fight against this disease.'
NBCU Photo Bank via Getty Images
9/16 Tom Hiddleston
Amyotrophic lateral sclerosis affects the brain and the spinal cord. Motor neurons degenerate and die which makes it increasingly difficult to move muscles
10/16 Rita Ora
There is no known cause of ALS, though there is a proven hereditary factor in some cases
11/16 Taylor Swift
There is also no known cure, though the millions being raised by the ALS association will go towards researching these great unknowns
12/16 Oprah Winfrey
The illness is also known as Lou Gehrig’s Disease, named after the all-time great baseball player from the early 20th Century whose time at the top ended when he was stricken with the illness in 1939
13/16 Mark Zuckerberg
The Facebook founder is unarguably the master of the challenge, who – following his drenching – saunters off
14/16 Justin Bieber
Bieber's first attempt was pretty naff: he didn’t quite get it and decided not to use ice or a bucket to complete the challenge. Obviously, the internet moaned at him and he was brilliantly peer pressured into having another go
15/16 Justin Timberlake
Celebrities have been nominating one another to do the challenge
16/16 Christiano Ronaldo and Marcelo
The challenge is now making its way over to this side of the Atlantic, former Manchester United players Paul Scholes and Gary Neville both doused themselves in cold water for a terminally ill fan
Damon was nominated by Ben Affleck and Jimmy Kimmel and said that he would also be donating to ALS.
He said on camera that the challenge was awkward for him “not only because there’s a drought here in California but because I co-founded Water.org and we envision a day when everybody has access to a clean drink of water – and there are about 800 million people in the world who don’t – so dumping a clean bucket of water on my head seemed a little crazy.”
“This is truly toilet water, I’ve been collecting it from various toilets around the house”, he said, chuckling.
“For those of you like my wife who think this is really disgusting, keep in mind that the water in our toilets in the West is actually cleaner than the water that most people in the developing world have access to.”
He added that it’s a “big problem and together we can do something about it”, before nominating George Clooney his “favourite actor”, Bono his “favourite musician” and Tom Brady the “greatest quarterback of all time”.
Video: Celebrities take on the ice bucket challenge
Water.org says that more people have a mobile phone than a toilet and that women spend 200 million hours a day collecting water in some regions.
In an interview with the charity, Damon said: “As a guy who has four daughters, this is a huge issue for women and girls: girls are often left to leave school and go find water, and that obviously has a huge impact on the quality of life they can expect to have.”