I found Sparkling Essence in our local health food store. It has no carbohydrates. The kids tried three of the four flavors currently available. JoJo likes Lemon while Nick prefers Mint. A package of four 10.5 fl oz. cans cost $2.99. Visit Knudsen Juices, put in your zip code and find a store close to you. For more information about this product, go to Knudsen Juices: Sparkling Essence

Here's a bit of info from the company website:

Sparkling Essence

Sparkling Essence™ combines the subtle flavor of organic lemons, cooling mint, whole blueberries, and fresh cucumbers with the tingling sensation of sparkling spring water. We use real organic ingredients, brew them in pure spring water, and then remove everything except the essence. The result: a light and refreshing flavor, but without any calories, added sugar, or artificial ingredients.