The ascendancy of coconut water as a trendy celebrity miracle cure-all is already facing a backlash, putting it in the same company as the poor mangosteen and acai berry— perfectly innocent natural foods whose reputations have been sullied by exaggerated health claims. No, coconut water isn't a substitute for blood plasma but it can be utilized for emergency rehydration, which of course makes it ideal as a hangover cure.
Many brands of coconut water crowd grocery shelves these days, most notably and recently an 11.8 ounce can of Goya brand agua de coco, (without added sugar or pulp) for a very reasonable 99 cents. The drawback of this and all the packaged brands is the packaging itself. It may be recyclable, but it certainly isn't compostable like a natural coconut shell. And in the case of the Goya brand, the naturally sweet and refreshing water carries with it a slight metallic aftertaste.
There is just no substitute for coconut water straight from the shell. Apart from a preservative-free, fresher-tasting flavor, there's something primally satisfying about lopping the top of a young coconut off with a machete (though it's been pointed out to me that this isn't a suitable activity to pursue while weathering the effects of a katzenjammer). And there's the added value of the jellied flesh that lines the interior of the shell.
Of course you can also add value to to your coconut water by adding booze, like former Graham Elliot barkeep Matty Eggleston does. He probably won't be making his version of the Caribeño Cocktail when he gets behind the stick at the forthcoming Bangers & Lace. But if you bring your own coconut water to him on Monday nights at Bar DeVille I'm sure he'd accommodate you. Or just go ahead and make it yourself:
2 oz. aged rum (Appleton 12-year works nicely)
3 oz. coconut water
1/2 oz. grenadine*
1/4 oz fresh lime juice (squeeze and drop in a wedge or two)
3 dashes Allspice Dram (or allspicey bitters like Bitter Truth's Decanter Bitters)
Shake with ice and dump back into shell. Or strain over fresh ice in a Collins glass.
* It's easy to make your own grenadine: reduce four cups of pomegranate juice down to two. Add two cups of sugar and dissolve. Cool.