Carbonated water (also known as club soda, soda water, sparkling water, seltzer water, or fizzy water) is water into which carbon dioxide gas under pressure has been dissolved. Some of these have additives such as sodium (seltzer water is almost always composed of water and carbon dioxide with no other additives). This process, known as carbonation, is a process that causes the water to become effervescent. Whether homemade or store-bought, soda water may be identical to plain carbonated water or it may contain a small amount of table salt, sodium citrate, sodium bicarbonate, potassium bicarbonate, potassium citrate, potassium sulfate, or disodium phosphate, depending on the bottler. These additives are often included to emulate the slightly salty taste soda water developed years ago from first using them as preservatives.