During his second year of medical school at the University of Louisville, John Mittel found himself hitting a wall while studying late one night. But he didn’t want a coffee, and sugar-filled energy drinks and soft drinks “have never given me that mental boost I was looking for,” he tells CNBC Make It. The med student settled for something healthy rather than caffeinated — a bottle of water. And that’s when he asked himself: Why can’t I have both? Nearly three years later, his Louisville-based start-up, Phocus, offers just that.

The caffeinated sparkling water comes in five flavors Phocus

After coming up with the idea to make caffeinated sparkling water in 2015, Mittel pitched it to his mentor, Tom O’Grady, a trader by profession who also invests in real estate and start-ups. They researched the industry, looked at trends and concluded that “the trends in beverage are all towards healthier, sparkling, no sugar types of things,” O’Grady tells CNBC Make It. O’Grady, who had quit a Diet Coke habit just before Mittel approached him, agreed to finance the endeavor. “I try to find trends and hop on them early and make a bet," he says. "And that’s what we’ve done here.” The entrepreneurs spent most of 2016 developing their brand and fine-tuning the Phocus formula: sparkling water infused with caffeine extracted from green tea, electrolytes and the amino acid L-theanine. The drink, which comes in five different flavors, has zero calories, zero sugar and no artificial preservatives. Each 11.5-ounce can has the caffeine equivalent of one cup of coffee, or about three cups of tea.

Phocus, which is in stores like Lucky’s Supermarket and can be bought on Amazon, officially hit the shelves on October 1, 2017. At that time, Mittel was less than a year away from graduating medical school and realized he had to choose between doing his residency in ophthalmology and building his company. If he tried to balance both careers, “I would have done one or both poorly,” he tells CNBC Make It. The decision was “definitely scary,” he says. “My family’s reaction ranged from my oldest brother and sister — both physicians — giving me the most push back, to my mom who told me, ‘Of course you’ve got to do Phocus.’” Ultimately, “I decided to pull out of ophthalmology and sell water.” That was in December 2017. He finished up med school, graduated in the spring of 2018 and since, has been working on Phocus full-time. “I’d be lying if I said the worry of paying off school debt doesn’t hang out in the back of my mind sometimes,” adds Mittel, now 28, who didn’t pay himself a salary in order to keep things lean until just after graduation. “But right now all my energy is directed toward growing and improving Phocus.”

Phocus