Coconut water is pink because the coconuts used to make the coconut water contains high levels of an enzyme called polyphenol oxidase.
Those polyphenol oxidase are what causes the coconut water to turn to a pink color and it's perfectly safe to drink pink coconut water.
The polyphenol oxidase is a natural antioxidant that naturally occurs in coconuts and by consuming that natural antioxidant your health benefits.
I love the pink colored coconut water much better than I do the regular color coconut water.
Not all coconut water is pink as I've seen some coconut water be clear and some white but it's okay for coconut water to be pink.