Carbonated water (also known as soda water, sparkling water, fizzy water, club soda, water with gas, in many places as mineral water, or especially in the United States as seltzer or seltzer water) is water containing dissolved carbon dioxide gas, either artificially injected under pressure or occurring due to natural geological processes. Carbonation causes small bubbles to form, giving the water an effervescent quality. Common forms include sparkling natural mineral water, club soda, and commercially-produced sparkling water.

Club soda and sparkling mineral water and some other sparkling waters contain added or dissolved minerals such as potassium bicarbonate, sodium bicarbonate, sodium citrate, or potassium sulfate. These occur naturally in some mineral waters but are also commonly added artificially to manufactured waters to mimic a natural flavor profile and offset the acidity of introducing carbon dioxide gas giving one a fizzy sensation. Various carbonated waters are sold in bottles and cans, with some also produced on demand by commercial carbonation systems in bars and restaurants, or made at home using a carbon dioxide cartridge.

It is thought that the first person to aerate water with carbon dioxide was William Brownrigg in 1740. Joseph Priestley invented carbonated water, independently and by accident, in 1767 when he discovered a method of infusing water with carbon dioxide after having suspended a bowl of water above a beer vat at a brewery in Leeds, England. He wrote of the "peculiar satisfaction" he found in drinking it, and in 1772 he published a paper entitled Impregnating Water with Fixed Air. Priestley's apparatus, almost identical to that used by Henry Cavendish five years earlier, which featured a bladder between the generator and the absorption tank to regulate the flow of carbon dioxide, was soon joined by a wide range of others. However, it was not until 1781 that carbonated water began being produced on a large scale with the establishment of companies specialized in producing artificial mineral water. The first factory was built by Thomas Henry of Manchester, England. Henry replaced the bladder in Priestley's system with large bellows.

While Priestley's discovery ultimately led to the creation of the soft drink industry—which began in 1783 when Johann Jacob Schweppe founded Schweppes to sell bottled soda water, he did not benefit financially from his invention. Priestley did however receive scientific recognition when the Council of the Royal Society "were moved to reward its discoverer with the Copley Medal" in 1772.