There is an excellently researched overview of seltzer history in the new issue of Moment magazine, and I don’t just say that because I am the resident “expert” she quotes.
Jewish Fizz: Seltzer, Egg Creams & Cel-Ray

“Carbonated water, the primary ingredient of these three Jewish champagnes, appeared first in European spas as a medicinal drink. Natural sparkling mineral water from the springs of a German village, Nieder-Selters—the linguistic origin for seltzer—was bottled and sold as early as 1728 in earthenware jugs, according to Barry Joseph, founder of Givemeseltzer.com and author of a forthcoming book on seltzer’s history. Said to cure all sorts of diseases, from the common cold to tuberculosis, seltzer was touted in an 1835 New York Times ad for ‘travelers…as the only sure preventative against the influence of a hostile climate.'”

Full link here.