Matt Damon has joined a long list of celebrities in taking part in the Ice Bucket Challenge, but decided to use toilet water to highlight the plight of unclean water in the Third World.
The Hollywood actor admitted dousing himself with water "posed a problem", as he is the co-founder of water.org, which campaigns for providing access to safe drinking water and sanitation in developing countries.
So far the non-profit charity has transformed hundreds of communities in Africa, South Asia and Central America.
Damon was nominated by friends Ben Affleck and comedian Jimmy Kimmel to take part in the viral challenge for the ALS Association (ALSA) which funds research into the incurable Lou Gehrig's disease, also known as amyotrophic lateral sclerosis, a debilitating neurological disorder.
The ALS campaign has gained the support of other high-profile celebrities and politicians, including former US president George Bush, Oprah Winfrey and Bill Gates, and has raised more than £53.3 million ($87.9m, €66.7m).
Speaking before the challenge, Damon said: "It posed a problem for me, because I co-founded water.org where we envision the day when everyone has access to a glass of clean drinking water. There are 800 million people who don't have this. So dumping water on my head seemed a little crazy.
"We also want to bring adequate sanitation for 2.4 billion people on planet earth who don't have it. So I thought a good thing to do was to tie those things together and take some toilet water.
"For those of you who think that this is truly disgusting keep in mind our toilets in the West are actually cleaner than the water that most people in the developing world have access to.
So as disgusting as this may seem, hopefully it will highlight the fact that this is a big problem and together perhaps we can do something about it.
"So I am happy to take the challenge and knock out ALS and for more information about the clean water and sanitation crisis please visit water.org."
Damon has now nominated his other big-name pal, George Clooney, to do the challenge next.