Coconut water is okay in moderation or if diluted in water. It is definitely healthier than soda. Because soda is one of the two worst foods according to Dr. Jonny Bowden. (The other food is french fries.)
The healthy part is because it contains five important electrolytes and minerals: potassium, magnesium, calcium, phosphorus, and sodium. [reference]
The main drawback is that it does contain some amount of sugar. And too much sugar is bad. David Getoff says in a podcast that he doesn’t consider coconut water healthy due to the sugar.