Carbonated water does not dehydrate you as long as there are no additives such as sodium or caffeine.
More Info: Carbonated water is merely pure drinking water with carbonation added. The carbonation process does not alter the water in any way as to promote dehydration. In fact, for those who do not particularly enjoy the taste of regular water, carbonation can be an incentive to drink more water in order to stay hydrated. The carbonic acids present in carbonated water may make some people feel fuller and more satiated.
Fact: Carbonated water can lead to dehydration if ingredients are added such as caffeine or sodium. These ingredients have a diuretic effect, which cause the body to rid itself of water. This in turn causes dehydration when adequate amounts of water are not restored.
Fact: Dehydration is a serious concern that can have both short term and long-term effects. Immediate signs and symptoms of dehydration include a feeling or dizziness or lightheadedness, irritability, and fatigue. Loss of vision, muscle spasms, vomiting, and unconsciousness are all possible effects if dehydration continues for extended periods of time. If dehydration occurs, fluid intake must be increased immediately.
Fact: Water is essential to all bodily functions. It helps cells, tissues, and organs to function properly. Without it, the body will eventually shut down. A great indicator of hydration is the color of urine. Clear to light yellow means that hydration levels are good. If the color resembles apple juice, dehydration is setting in.