"So this is just something you do in the movie? " host Jimmy Kimmel asked his guests.
"No, we just do it in life," 22-year-old Woodley deadpanned. "It's just insane." (Ironically, in the best-selling Divergent book series, 29-year-old James' character Four is afraid of heights.)
Kimmel then asked Woodley if it's indeed true that she collects her own water from local springs.
"That's correct. It's the only water I try to drink, but we travel so much," said the leading lady, who added that she visits the mountains "when I'm home, when I have the time."
"There are a lot of mountains with a lot of water. There are natural springs," Woodley continued. "There's this amazing database called findaspring.com, and it kind of lists where all the springs throughout the world are: hot springs, cold springs. It's really fantastic...You have to be careful about it, though. You could have some danger zones—something funky in the water."
Kimmel jokingly asked James if he's ever tried Woodley's "malaria-infested" water.
"It's incredible, yes," he replied. "She puts me to shame. She's extremely healthy, organic, everything."
What does James typically drink? "Just straight vodka," the English actor quipped.
"Do you share that water with people?" the late-night TV personality asked Woodley. "Because if I went up to the mountains and got my own jug of water, I would save it all for myself."
"There is so much water!" the Golden Globe-nominated actress promised. "You bring these 5-gallon little carboy situations, you fill them up, take 'em home, put 'em in the trunk. Good for a month."
Before unveiling the final Divergent movie trailer, Kimmel asked the actors if they were nervous about starring in the blockbuster film adaptation of author Veronica Roth's novels. Kate Winslet, Ashley Judd, Tony Goldwyn, Zoë Kravitz, Ansel Elgort, Maggie Q, Jai Courtney and Miles Teller also star.
"We both talked about it, and it's something that you need to really have a bit of a think about, to contemplate how it's going to change your career and your life," said James, who's also appeared in Downton Abbey and Golden Boy. "By the same token, you don't know what anything's going to be.
"I think sort of the lack of anonymity would be the most daunting factor in taking on a movie like this," Woodley agreed. "But you never know! You never know what's going to happen."
Divergent hits theaters on Friday, March 21.