"Coconut water is low in fat and calories, has no cholesterol, and has a natural balance of sodium, potassium, calcium and magnesium- making it a healthy electrolyte drink. It has even been used intravenously to stabilize electrolytes... Since it regulates the functioning of the intestine, the coconut water propitiates to the user a smoother and pretty skin. Beyond ingested, the coconut water can also be used directly on the face, for skin hydration." source
I love that there are so many benefits to coconut water but what I really adore is the taste. It's part refreshing, part hydrating, not too sweet, not too bitter, just the right amount of flavor mixed with water. It taste quite like a coconut watered down.
Coconut water has become so sought after that they basically sell it in every liquor store/ bordella/ gas station/ convenience store/ supermarket near you.
Zico is a great choice (the one I drink). You can find it in a plastic bottle or a cardboard box. It retails for around $3.25.
VitaCoco is also very popular and comes in a cardboard box. It retails for about the same amount.
If you desire completely fresh coconut juice, they have that too. It's harder to find but if you type in "fresh juice" and your location, you should find a place that makes fresh juices and, alas, coconut water too.
In NYC, Liquiteria is a great option. In LA, try Beverly Hills Juice.