carbonated water

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Effervescent water charged under pressure with carbon dioxide gas, used as a beverage or mixer.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Water containing carbon dioxide dissolved in it under pressure. This is not to be confused with Soda Water which is an entirely different substance because if it lost its carbonation, it would be called de-carbonated soda water.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun effervescent beverage artificially charged with carbon dioxide