Coconut water is low calorie and full of minerals.

Coconut water has become Britain’s fastest-growing soft drink. It’s made by extracting the milky fluid inside unripe green coconuts (this turns to milk when the coconut is ripe) and can be drunk as is or flavoured with sugar and fruit juice.
The drink, which tastes like slightly sweet, slightly salty water, is low in calories and said to be high in minerals such as potassium and magnesium, which are vital for muscle movement, nerve transmission and brain operation.
These minerals are depleted after exercise, so coconut water is often sold as a post-workout drink.