People drink far more still bottled water than sparkling water these days, and the gap has been growing fast, according to market research firm Canadean. Global per capita bottled non-carbonated water consumption has grown from about nine liters (300 fluid ounces) per person in 1999, to nearly 27 in 2013—an almost 200% jump. Meanwhile, bottled sparkling water intake per person has grown by a paltry 13% to six liters per person.

The gap is even more pronounced in the US, where Americans drink more than 90 liters of bottled still water per person, but less than five liters of its carbonated counterpart annually on average. The difference is so pronounced that it’s virtually impossible in the chart below to make out the fact that sparkling water consumption per capita has risen quite a bit, too—by over 160% since 1999.

Demand for bottled water has been climbing for a few reasons. The growing middle class in countries such as India and China is increasingly foregoing tap water for filtered and bottled water. China’s bottled water market has grown by 230% since 2008, according to Zenith International. The forecast is that China will soon drink more by total volume than the US. In countries like Mexico (which consumes more bottled water per capita than any other country in the world), consumers opt for bottled water because of concerns about the safety of tap water. There’s the decades-long marketing effort by the bottled water industry to position the packaged stuff as healthier. And some consumers have substituted bottled water for soft drinks in order to cut down on sugar and calories.

And why is consumption of sparkling water growing so much slower than still? There is some popular buzz around home carbonation, which companies like SodaStream are capitalizing on. But there are also a number of things working against bubbly water. It can be more expensive. And it doesn’t appeal as directly to consumers switching to bottled water out of health concerns. “There’s a growing consumer shift in some traditional carbonated water markets to still water for health reasons,” Antonella Reda, an industry analyst at Canadean, told Quartz. Sparkling water sales have been tepid at restaurants too, Reda said. She forecasts still water will only widen its lead over sparkling in per capita consumption globally over time.