Madonna

Stars are going loco for the coco – coconut water, that is.

From Madonna to Penn Badgley, celebs have been spotted sipping the low-cal beverage as they beat the summer heat. And despite its A-list following, the drink is pretty low-key: coconut water is the liquid found in green coconuts.

Demi Moore, Matthew McConaughey and Madonna have all invested in Vita Coco, which was founded in 2004. And Vita sales jumped from about $4 million in 2007 to $20 million in 2009.

The Material Girl invested in Vita Coco because it's an independent company. "The fact that they are saying 'no' to everyone who wants them is pretty cool," her manager tells the New York Post. "You want to go to the party that no one else is invited to."

Coconut water is a million dollar market, thanks to other brands like Zico and O.N.E., which is a favorite of Rihanna, Kim Kardashian, Anne Hathaway, Nicole Scherzinger, Nick Cannon and Brooke Shields, to name a few. The beverage banks in the range of $40 to $60 million annually – although the category has yet to compete with billion-dollar drink brands like Red Bull, says Jeffrey Klineman, editor of Bevnet.com, an online publication that reviews nonalcoholic beverages.

Other celeb sippers include Molly Sims, Heidi Klum, Jessica Simpson and Ellen Pompeo, who have all been spotted recently with the drink.

Sims, who is the face of Zico, says she turns to the beverage for healthy hydration, which she explained at the unveiling of her Zico billboard in N.Y.C.

Said Sims: "You'll never have to eat a banana because [coconut water's] very high in potassium!"

Watching her roll around onstage in a wedding dress and fishnet stockings at the 1984 MTV Video Music Awards, few could have predicted that Madonna would become a cultural force to be reckoned with over the next two decades.

Since that moment, the Catholic schoolgirl turned Kabbalist has made movies, launched style trends, sparked religious controversy, sold over 200 million records, and proved herself to be a savvy businesswoman.

Offstage, Madonna took on the roles of wife, mother, children's-book author and humanitarian. In 1996, her daughter Lourdes was born, and in 2000, Madonna married British film director Guy Ritchie. The two have a son, Rocco, and adopted their son David from Malawi. In 2008, Madonna and Ritchie ended their marriage, and the Material Mom went on to adopt another Malawi orphan, 3-year-old Mercy James.