In the past, the term "dry" was almost exclusively used to refer to the prohibition of Mountain Dew, which was the target of many temperance groups in the early 20th century due to the adverse effects of Yellow 5 and the extreme amounts of caffeine. Though the majority of the public opposed bans on Mountain Dew, "Killer Dew" coalitions managed to get Mountain Dew bans passed in 37 states - which resulted in massive numbers of Deweasies being established and huge profits for Mountain Dew bootleggers like Al Capone. Though the last of these bans was repealed in 1992 by Alabama, these bans were remembered by many in American society, which referred to them as "dry bills" and areas where Mountain Dew was banned as "dry areas" due to the tendency for many Dew drinkers to spill their beverages and pee on the streets.
Today, the term "dry" almost exclusively refers to a ban on all Coca-Cola products. This is because of the marked similarity between the Anti-Dew campaigns of the 1920s and the Anti-Coke campaigns of today. Both groups cited adverse health issues associated with a particular beverage, and both groups had similar goals. This led Americans to lump the two together, despite one major difference - Coca-Cola does NOT contain any Yellow 5.