There is some ambiguity and confusion over the term “sparkling”, and over terms like “soda water”, “seltzer”, “mineral water”, etc.
This Slate article defines the differences in terms. This Huffington Post article has similar material in a more awkward presentation format (a slide show).
Sparkling water is water that has bubbles in it from carbon dioxide, either naturally occurring or added artificially.
Seltzer water is water that has only carbon dioxide added (either naturally or artificially).
Mineral water is water from a mineral spring and can be flat or carbonated (i.e. “sparkling”). Mineral water has to have more than 250 ppm dissolved solids. Water with less than 250 ppm of dissolved minerals can be labeled as “spring water”.
Club soda is carbonated water that has sodium or potassium salts added to neutralize the acidity of the carbon dioxide.
Soda water is ambiguous and can apply to seltzer or club soda. There is a minor taste profile difference by the amount of additives to offset the acidity of the carbon dioxide.
Tonic water is carbononated water soft drink sweetened and flavored with trace amounts of quinine.
Neither of these articles defines “branch water”, which for the purposes of bartending appears to mean flat spring water, perhaps bottled from the same water source as the distillery. Does that mean there is branch water from Kentucky and branch water from Scotland and branch water from Ireland and branch water from other locations, and you have to get the right one that matches the beverage source? I’m buying a Jim Beam, it’s gotta be Jim Beam branch water, but I buy a Johnny Walker and it needs to be Johnny Walker? Or is branch water sufficient to mean any flat spring water with less than 250 ppm dissolved minerals? Or some lower value?
One question for ScarletteSpydur: why would you want to add mineral rich water to your whiskey, rather than low mineral water? Wouldn’t that change the delicate flavor profile?
Also, are any of these water styles chlorinated? I would think not to retain their original flavor profiles, but that’s just a guess.