Drew Barrymore Shares the Piece of Advice 'Best Friend' Cameron Diaz Has Been Telling Her 'Since the '90s!'

Drew Barrymore admits "best friend" Cameron Diaz is her biggest coach in one important area of her life: living green.

"I made a promise to my best friend, Cameron Diaz, that I would become someone who she had been pushing me to be my whole life, which was environmentally aware, conscientious and living a certain lifestyle that was sustainable," Barrymore says in a chat with PEOPLE about her partnership with environmentally conscious home supplies company Grove Collective and the Virgin Group, alongside its founder Sir Richard Branson.

"She's been saying this since the '90s to me," the actress continued. "Once I started living that way and really committing, [I] saw the world differently and it made me put it all into practice and action."

Not only has the Stand-In star, 47, ditched her "favorite thing in the world," Ziploc bags, but she's also found other ways to be more sustainable with pointers from Diaz.

"Cameron would literally be like, 'Stop letting the water run while you're brushing your teeth! Don't do that!' And she always felt like that big sister, leaning into me," Barrymore adds.

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Her appreciation for the natural world was recently put on display when a video she posted of herself dancing in the rain went viral on social media. "Whenever you can go out into the rain, do not miss the opportunity!" the smiling star said in the clip, looking up at the sky and laughing.

RELATED: Drew Barrymore's Video of Her Dancing in the Rain Goes Viral: 'Do Not Miss the Opportunity!'

She tells PEOPLE that she "didn't have any preconceived notions about what would happen" when she posted the viral video; it was simply a way to express the importance of "living in the moment."

"I'm such a hippie that when I see the rain, I just think I want to go out in it and have a little baptism from Mother Nature and be free and not worried for a second," she says. "Because I do worry and stress a lot. I'm also not a hippie [sometimes] and really a person who wants to have action and be a business person and get things done. And with that comes a tremendous amount of pressure and stress…Rain is a signal for me to let go and stop overthinking everything."

Barrymore also sings the praises of her co-star in the Grove Collaborative campaign video, Richard Branson, saying that "there is this enjoyment and optimism" that the billionaire businessesman puts out in the world.

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Grove Collaborative

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When it comes to combating the plastic crisis, the Virgin Group founder tries to "practice what I preach" by avoiding single-use plastic products and making changes in his own business ventures, including his all-inclusive, adults-only cruise line, Virgin Voyages.

"We have influence over some quite large companies. So, if you take something like Virgin Voyages, there won't be single-use plastic on it. There won't be straws that are plastic. There won't be water bottles that are plastic. There won't be shopping bags that are plastic," he adds.

Barrymore adds that sustainable change requires group efforts: "We need the micro and the macro. We need companies and people who change the world and are real game changers, as well as our own little individual efforts."