Interestingly, Walgreens actually based their store structure off of smaller drugstores, such as Abbotmaid. In describing their history, the Walgreen’s website describes the evolution of the early drugstore into a soda fountain:

“Beginning in the early 19th century, bottled soda water, and later charged soda water, were considered important health aids, making it a natural fixture in drugstores. To dispense the icy-cold, charged water, a tin pipe and spigot were attached. Soon, flavored syrups were added to the fizzy water and still later, ice cream added to that. As sodas grew in popularity, so the ‘soda fountain’ grew in beauty, ornamentation and importance as a revenue source to the drugstore.”


Sources
[1] “Our Past.” Walgreens: Trusted since 1901., www.walgreens.com/topic/about/history/hist3.jsp.