For those who prefer sparkling water over still, there is scant evidence that sparkling is all that much less healthful than regular.
While extensive studies have not been done, carbonated water seems to present a negligible health risk in most circumstances. A far greater risk, most experts believe, is the failure to drink enough water.
People with some disorders such as esophageal reflux are often told to avoid carbonation, and a few drugs should be taken only with plain water. Too, most bottled waters lack the tooth-hardening fluoride that is added to many public water supplies.
Most studies suggesting that the acidity in carbonated beverages harms tooth enamel implicate flavored beverages, not carbonated water, club soda or seltzer. The handful of studies that did include carbonated water found a risk to extracted teeth that were immersed in it, but it was a very low one. One study found that sparkling mineral waters produced slightly greater dissolution of tooth material than still waters, but levels that were only 1/100th of those of the flavored soft drinks tested.
High sodium levels in some bottled waters present a risk for some people, but a study in Spain, reported in 2004 in The Journal of Nutrition of the American Society for Nutritional Sciences, suggested that a sodium-rich carbonated mineral water might reduce cardiovascular risks in postmenopausal women.