Drew Barrymore says Cameron Diaz has spent years trying to teach her how to be more environmentally-friendly.

The 'Charlie's Angels' co-stars have been friends since the 1990s and Drew has revealed she made a promise to eco warrior Cameron to embrace sustainable living and she tries to take on plenty of her pal's useful green living tips.

Drew told PEOPLE.com: "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.

"She's been saying this since the '90s to me. 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."

The 47-year-old actress revealed she has made an effort to ditch plastic food storage bags, which she describes as her "favourite thing in the world," and now also makes an effort to switch the water off when she's brushing her teeth.

She added: "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."

Cameron is a longtime champion of environmental issues and previously explained how she tries to make a difference every day but just doing small things at home.

In an interview published on Huffpost.com, she explained: "I just do as much as I can do, all the basics that everybody does ... be aware of my energy consumption, as far as all the lights in my house, how much power I use, how much I run the water, set my thermostat, my recycling, my car - I drive a Prius - I've driven a Prius since they've been out."

Cameron also tries to off-set her carbon footprint as she has travelled so much for work over the years. She added: "I do my carbon offsetting for my travels because I travel so much. My travel agent just basically tallies it as I go. I'm building my houses and stuff - I am trying to retrofit everything as much as possible and also other projects that I have going on I try to do it consciously, as green as possible. And I am just trying to help spread the word."