LaCroix Sparkling Water has been a little-known secret for 30 years, according to Vox. But suddenly, it's become a favorite among career women and has developed a huge following. Business Insider reports that that the sparkling water's sales have leapt from $65 million in 2010 to $226 million in 2015 and it is now the number one flavored water in the U.S.This sudden sales spike leads to one big question: Why is LaCroix suddenly a popular drink? The answer is simple, of course: millennials.According to Business Insider, LaCroix has avoided traditional advertising, which plays directly into millennials being able to discover it on their own."With millennials these days, it's all about authenticity and discovery, and they are suspicious of mainstream advertising messages," Duane Stanford, editor of Beverage Digest, told Business Insider."Millennials see [LaCroix] as a discovery — something only they know about and their friends know about, since it's not in their face all the time," Stanford continued.Instead of doing traditional TV and radio advertisements, LaCroix paid fitness bloggers to promote the sparkling water. So, it's also been presented as an alternative to soda. That's really a win-win. Millennials — who are moving away from consuming soda in favor sparkling water — are able to get a kick of flavor with endorsements from bloggers they consider reliable, reports Vox.LaCroix is reaping the benefits of millennial obsession, one can of flashy sparkling water at a time.