To move from conjecture to fact, coconut water is water comes from immature coconuts. (Coconut milk is the result of hot water and mature coconuts. Two very different products.) To this day, a Grok descendant whacks the top of the "nut" off, or punches a hole in an "eye" and drinks.
It's carbs, 1/3 fiber and 2/3 sugars. a bit of fats, surprisingly good proteins, and very good potassium. About 18 times that found in Gatorade.
I don't think the brand matters, it shouldn't. I guess you could be on the lookout for preservatives or something.
And BTW, if one does go the Gatorade route, use the powdered. The liquid uses HFCS first, and sucrose second. The powder of course has no HFCS and also has slower release dextrose.