Even as anti-obesity campaigners like Mr. Nutter have failed to pass taxes, they have accomplished something larger. In the course of the fight, they have reminded people that soda is not a very healthy product. They have echoed similar messages coming from public health researchers and others — and fundamentally changed the way Americans think about soda.

Over the last 20 years, sales of full-calorie soda in the United States have plummeted by more than 25 percent. Soda consumption, which rocketed from the 1960s through 1990s, is now experiencing a serious and sustained decline.

Sales are stagnating as a growing number of Americans say they are actively trying to avoid the drinks that have been a mainstay of American culture. Sales of bottled water have shot up, and bottled water is now on track to overtake soda as the largest beverage category in two years, according to at least one industry projection.

The drop in soda consumption represents the single largest change in the American diet in the last decade and is responsible for a substantial reduction in the number of daily calories consumed by the average American child. From 2004 to 2012, children consumed 79 fewer sugar-sweetened beverage calories a day, according to a large government survey, representing a 4 percent cut in calories over all. As total calorie intake has declined, obesity rates among school-age children appear to have leveled off.

The change is happening faster in Philadelphia than in the country as a whole. Daily soda consumption among teenagers, a group closely tracked by federal researchers, dropped sharply — by 24 percent — from 2007 to 2013, compared with about 20 percent for the country. Last month, the city Department of Public Health reported a sustained decline in childhood obesity over the last seven years.