Water vs. Soda
Soda pop is liquid candy. It's a sweet treat to be enjoyed occasionally, but most people cannot fit it into a healthy diet every day.
Soft drinks (soda, "fruit" drinks, sweetened teas, sports drinks, etc.) are the largest source of refined sugars in Americans' diets. Would you ever sit down and eat 16 teaspoons of sugar? That's how much sugar is in a 20-ounce bottle of soda. That's more refined sugar than you should eat in a day (for a typical kid eating about 2,350 calories, health experts recommend eating no more than 13 teaspoons of refined sugar a day).
Kids who drink more sodas and other soft drinks eat more calories and are more likely to be overweight. The calories you drink don't seem to register as well as the calories you eat from solid food. So when you add a 20-ounce soda to your lunch, you probably won't make up for it later by eating 250 fewer calories of solid food.