Coconut water should certainly not be mixed up with coconut milk, the milky fluid which is made by mixing grated coconut flesh with water. Coconut water is the liquid that is inside  the coconut, which is the reason why it is called coconut water and not coconut juice. Juice is what remains of a fruit which has been squeezed out and consists of the fruit sugars of that particular fruit. Depending on the fact whether the producer himself adds any sugars of not, the sugar content can be fairly high.