The beverage aisle offers various options for bubbly water, often leading to confusion as terms like seltzer, sparkling water, and club soda are used interchangeably. All these drinks share dissolved carbon dioxide ($\text{CO}_2$), which creates the effervescence, but their origins and ingredients are distinct. The primary distinction lies in how the carbonation is introduced and whether mineral salts are naturally present or intentionally added.
Seltzer vs. Sparkling Water: The Key Distinction
Seltzer is defined as plain water that has been artificially carbonated by injecting pressurized carbon dioxide ($\text{CO}_2$). This process results in a clean, crisp, and neutral taste because seltzer is free of naturally occurring minerals and added salts. Its simplicity makes it a blank slate, often used as the base for flavored carbonated beverages.
Sparkling water, in contrast, is naturally carbonated, meaning the carbon dioxide occurs naturally in the source, such as an underground spring or well. This natural source also means the water often contains minerals like potassium, magnesium, and sodium. The presence of these minerals gives sparkling water a more complex and sometimes subtly salty or mineral-like taste compared to seltzer’s neutral profile.
Club Soda: The Mixer
Club soda is a type of carbonated water that is artificially carbonated, similar to seltzer. However, the defining feature of club soda is the purposeful addition of mineral salts. These added compounds typically include sodium bicarbonate, sodium citrate, potassium sulfate, and disodium phosphate.
The addition of these mineral salts is intended to mimic the flavor profile of naturally carbonated mineral waters and to neutralize the slight acidity created when $\text{CO}_2$ dissolves in water. This composition gives club soda a slightly more savory or metallic taste than seltzer. Club soda is traditionally favored as a mixer in cocktails, where the added salts can enhance the overall taste of the drink.
Sparkling Mineral Water: The Natural Option
Sparkling mineral water is sourced from a protected underground spring or well and is defined by its high mineral content. To be classified as mineral water by the U.S. Food and Drug Administration (FDA), the water must contain at least 250 parts per million (ppm) of total dissolved solids (TDS). These dissolved solids are naturally occurring minerals that are absorbed as the water flows through rock and soil.
The carbonation in sparkling mineral water can be naturally occurring, or it may be added back in if some of the natural $\text{CO}_2$ was lost during the bottling process. The high concentration of minerals, which can include salts and sulfur compounds, gives this water a distinct and often stronger flavor profile than other carbonated options.