What exactly is the difference between Club Soda and Seltzer Water?

Question

They seem/appear to be the same thing (sparkling water) yet are called two different things. On top of this the same brand might have a ten or twenty price difference between lets say Cotton Club Seltzer and Cotton Club Club Soda (no flavoring added to either). Is there a difference?

Answer 1

The only difference would be amount of sodium.  Otherwise there is no difference at all.

Answer 2

According to Cook's Encyclopedia: Seltzer water is a flavorless, naturally effervescent water that takes its name from a region of Germany. Club soda, sometimes called soda water, was introduced in the later half of the 18th century when carbon dioxide was injected into water. Seltzer and club soda are essentially the same, except one is naturally effervescent and one is man-made.