Hugh Jackman’s own superpower: the ability to drink gallons of water in a single day.
While he’s appeared incredibly pumped up in his previous turns as Wolverine, Jackman and director James Mangold decided that for his outing in Friday’s “The Wolverine,” the actor was going to have to get even bigger. “Veiny” big. His arms could be read by a blind man.
“I think this is the best or closest to the way that I imagined the character,” Jackman tells The Post. To get the ripped silhouette he’d always pictured but never had enough time to build in a gym, Jackman deployed an old bodybuilding trick.
Ahead of key shirtless scenes, he went on a dehydration diet, guzzling up to four gallons of water every day for a week. Then he’d stop drinking all liquid for 24 hours.
“You can lose up to 10 pounds of water weight, particularly the water that sits under your skin,” Jackman says. “It really cuts you up.”
The actor also trained for months, working out three hours a day over two sessions. For diet help, he turned to Dwayne “The Rock” Johnson. The advice: Pack away 6,000 calories worth of lean meat, fish and vegetables. Every. Single. Day.
On Jackman’s Twitter account, the actor occasionally posted photos of that day’s menu, which looks like take-out for five people, with rows of containers stuffed with salmon, chicken breast and steamed broccoli. He jokes that “digesting food” is his main occupation now.
Besides helping his body look particularly jacked, the dehydration diet served another purpose: It helped the actor get into character.
At a time when every celebrity foible winds up on YouTube, nary a bad word has tainted Jackman’s long showbiz career. He seems to be one of Hollywood’s truly nice guys, which makes his transformation into Wolverine even more remarkable.
Wolverine — a k a Logan — is a vicious killer, a mutant born with sharp claws that extend from his knuckles and a healing factor that repairs wounds and makes him virtually immortal.
Wolverine was recruited into a secret government program, his bones coated with an indestructible metal and his memory wiped. He eventually joined mutant superteam the X-Men to fight for good, but he continues to be tortured by his past and his animalistic nature.
Meanwhile, Jackman, 44, enjoys show tunes.
Playing the killer required its own method, starting with that dehydration diet. “Trust me, that really pisses you off,” Jackman says. “I wouldn’t recommend that for everyone.”
He also begins each day with a cold shower, because that’s a good “physical trigger” to becoming angry. The morning workouts are also key.
“That kind of zone you need to be into with that intense training is similar to the state that Wolverine lives in all the time,” he says.
Jackman no doubt puts so much into playing the mutant superhero because landing the role helped turn him into a superstar. (He scored the Wolverine gig after fellow Aussie Dougray Scott got held up making “Mission: Impossible 2.”)
“The Wolverine” marks Jackman’s sixth outing as the character, beginning with “X-Men.” Considering that most franchises get rebooted and actors replaced after three films, having a single man play the role for more than a decade is quite a feat.
So 13 years on, a lot is riding on “The Wolverine,” in part because the character’s first solo outing, 2009’s “X-Men Origins: Wolverine,” was considered a dud by critics and fanboys alike.
“Oh, yeah. I’m aware of the disappointment [some people felt], and on some level, for good reason,” the actor says. “Everyone would stop me in the street to tell me all about it. It’s a character that’s been around for a while, and people are passionate about it, and they’re not bashful in coming forward.”
Jackman promises that this movie will be different, presenting a purer picture of the character. The plot is based on one of the most beloved comic book arcs in history, 1982’s “Wolverine” by writer Chris Claremont and artist Frank Miller (of “Sin City” and “Batman: The Dark Knight Returns”).
Jackman first read the series preparing for “X-Men” and immediately told producer Lauren Shuler Donner, “Now this is a movie!” He’s been waiting 13 years to see it on-screen.
“The Wolverine” finds Logan traveling to Japan at the behest of a dying former soldier, whose life the hero saved during World War II. Once there, Wolverine hooks up with the old man’s granddaughter, Mariko (Tao Okamoto), battles ninjas, yakuza and the armored Silver Samurai (Will Yun Lee). He may also lose his healing power.
“I always thought it would be a great juxtaposition to have this guy in Japan, because in many ways, he embodies the opposite of all Japanese traditions and honor and codes,” Jackman says. “He’s a lone wolf. He does what he wants.”
As the film progresses, Wolverine learns to appreciate the Japanese way of life. “This is a person who’s lost. He’s a warrior but he’s struggling to find purpose,” Jackman says. “That whole code of the samurai and honor and bravery and him coming to respect that and know himself is a really good canvas for the writers to work with.”
The movie could have been very different. Initially, Darren Aronofsky of “Black Swan” was hired to direct. He later dropped out of the project, saying he was reluctant to spend so much time overseas away from his family, but rumor had it that he bolted after clashing with the studio over the film’s rating. Aronofsky was supposedly keen to do a hard-edged, blood-soaked, R-rated adventure.
Jackman says that’s not entirely true and that Aronofsky wasn’t completely sold on making a film for adults. “At the end of the day, even Darren was aware that I run into so many 12-year-olds or 13-year-olds [to whom] Wolverine is not just cool, he’s very important,” Jackman says. “To deliberately exclude them was never something we were going to do lightly.”
For fans who love Jackman in the role that made him world-famous, this may well be one of the last times to see him on screen. The 44-year-old is currently shooting the sequel to “X-Men: First Class,” called “X-Men: Days of Future Past,” and after that, he doesn’t yet have plans to strap on the claws again.
“I don’t want to tease you and say this is the last one,” Jackman says. “But my basic philosophy is that I go movie-to-movie and see how it all goes, but if I don’t feel I have anything new or different to offer or the story doesn’t progress in some way, then I won’t be doing it.”
So, yes, there may come a time for someone else to grow those iconic muttonchops. But here’s hoping not for many years.
Wolverine’s foxes
It’s hard being 150 years old, like Wolverine. For one thing, good luck finding a lady to be with you (unless it’s Anna Nicole Smith). Throughout his six on-screen appearances, Wolverine, a k a Logan, has had quite a few relationships with females — none of them healthy. Here’s a refresher.
Kayla Silverfox
Wolverine is living peacefully in the Canadian wilderness with his love in “X-Men Origins: Wolverine” until Sabretooth (Liev Schreiber) shows up and supposedly murders her. At the end of the movie, Logan discovers that Silverfox (played by Lynn Collins) didn’t actually die, but is alive. In the end, she sacrifices herself for her love.
Jean Grey
Grey (Famke Janssen) is a member of the X-Men with telekinetic powers. Although she was engaged to Cyclops (James Marsden), Grey also finds herself attracted to Wolverine. In “X-Men: The Last Stand,” Wolverine is forced to kill her after a dark power known as the Phoenix possesses her, leaving him devastated. She appears in dreams to Logan in “The Wolverine.”
Mariko Yashida
Logan’s love interest in “The Wolverine” is played by newcomer Tao Okamoto, an actor that Hugh Jackman, who is also a producer on the movie, helped personally select. Mariko is the granddaughter of a billionaire Japanese tycoon whose life Wolverine saved during World War II. After the old man dies, Logan is forced to protect Mariko from money-hungry criminals.
Viper
An evil mutant (played by Russian Svetlana Khodchenkova) in a slinky green dress whose kiss means death. She pursues Wolverine and Mariko in Japan during “The Wolverine.”
reed.tucker@nypost.com