As I’ve focused more on writing the book and less on this blog, my comments about the project tend to appear more often on the Facebook page dedicated to the project.
But I am playing now with Google’s Ngram viewer, that lets you search for occurrence of words to unearth hidden meanings. Let’s look at how often seltzer is seen in different countries over different times.
I use “seltzer” plus “seltzer water” plus “Seltzer Water.” I don’t use the seltzer as a proper noun, “Seltzer,” which it certainly was in the beginning, because it is not possible to distinguish from the current surname.
In English:

This now focuses just on American English, starting from its lowest year, 1854, to 2007: