Water that has been highly charged with carbon dioxide, which gives it effervescence. Soda water, also called club soda or just plain carbonated water, contains a small amount of sodium bicarbonate, which, because it's alkaline, can help neutralize an acidic stomach. Soda water is combined with sweeteners and flavorings to produce a variety of soft drinks. Many cocktails also use soda water as an ingredient.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.