Seltzer water, also called soda water or club soda, is artificially carbonated water. Seltzer water is named after a natural spring in Germany, but in imitation of it and not because it is derived from there. Naturally carbonated water is called sparkling mineral water.
Seltzer is made by pressurizing water with carbon dioxide gas so that the gas is forced to dissolve into the water. The pressurized gas forms tiny bubbles of fizz. Depressurizing the beverage, such as by opening a sealed bottle of seltzer, releases the gas and creates the familiar hissing and popping noises associated with opening carbonated beverages.