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What he's doing:

Actor and producer Mark Wahlberg is no stranger to the world of fitness as attested by everything from those shirtless Calvin Klein ads to his recent role as a boxer in The Fighter. He's now exploring another way to make fitness pay; last year he became an investor and board member of AquaHydrate, an "enhanced" bottled water targeted at workout warriors. AquaHydrate says it isn't yet profitable, but Wahlberg may be catching this wave as it crests; AquaHydrate says 2010 sales were up 64 percent from the previous year, and it recently got an infusion of $10 million from venture capitalist Ron Burkle.

Why it's promising:

Enhanced water is now a heavyweight in the beverage world, analysts say. Recently, the category's sales rose slightly, even as revenues slipped for fruit juices and carbonated drinks. Consumers are drawn to the perceived health benefits, and sellers can charge a premium a 1-liter bottle of AquaHydrate typically retails for around twice the price of plain bottled water. "Niche products are the future of the beverage industry," says Gary Hemphill, managing director at consulting firm Beverage Marketing.

What's next:

Wahlberg, who had already racked up business experience as a partner in a production company, works with AquaHydrate on everything from bottling plans to closing deals with new investors. Notre Dame professor James H. Davis says investors with active roles like Wahlberg's often do well, since they can keep close tabs on their firms. When SmartMoney caught up with Wahlberg, he told us he's glad to be diversifying beyond Hollywood. "I don't want to rely on whether I'm 'hot or not' for that long," he says.