Club soda is a soft drink closely related to soda water, except that it contains a small amount of salt for flavor. Sometimes, however, club soda is used as a synonym for soda water; see that article for details.
The composition of club soda varies among different brands. The most common additions are sodium citrate and sodium chloride; other possible ingredients are sodium bicarbonate, potassium sulfate, and disodium phosphate. The total amount of sodium is usually comparable to other flavored soft drinks.
Club soda containing sodium citrate has a slightly sour flavor (similar to citrus fruits), noticeable when consumed by itself and in certain mixed drinks, but usually not strong enough to be detected when mixed with stronger flavored beverages, such as juice. It is often used as a substitute for plain soda water, commonly as a mixer.
Carbonated water, also known as soda water, sparkling water, or seltzer water, is plain water into which carbon dioxide gas has been dissolved.
Clubsoda may be identical to plain carbonated water or it may contain a small amount table salt, sodium citrate, sodium bicarbonate, potassium bicarbonate, potassium sulfate, or disodium phosphate depending on the bottler.
Joseph Priestley first discovered a method of impregnating water with carbon dioxide when he suspended a bowl of water above a beer vat at a local Leeds brewery.