Coconut water contains electrolytes, and is often used to re-hydrate after exercising instead of drinking sports drinks, which contain lots of sugar. One cup of coconut water contains about 46 calories. Carbs make up the majority of the calorie content, about 8.9 grams per 1-cup serving, of which 6.26 grams are from sugar. Coconut water is a good source of the electrolyte potassium, and provides 600 milligrams per 1-cup serving. It also contains about 250 milligrams per-serving of sodium, another electrolyte lost during exercise through sweat. The potassium and sodium content found in coconut water is a smart choice when you become dehydrated, whether from physical activity or sickness. One serving of coconut water also provides about 6 milligrams of vitamin C, along with folate, riboflavin, thiamin, niacin and vitamin B-6 and key minerals including calcium, iron, magnesium, phosphorus and zinc.