The Bourne Identity star shot a spoof press conference in which he pledged not to use the bathroom until everyone in the world has access to clean water and sanitation.
The clip was later turned into a public service announcement (Psa) for his Water.org campaign which aired earlier this year (Jan13) and now Damon's celebrity friends have shown their support for the initiative.
In a new Psa, Biel, Bateman and Gad jokingly reveal their unique take on the strike and how they've managed to make good on their commitment.
Biel reveals, "I've never gone to the bathroom in my entire life", Gad insists he has not used a bathroom for four days, and Bateman jokes he has been using a sink to relieve himself in.
Damon ends the clip by inviting viewers to "join the millions of famous people who've already joined" his strike.