Q. What bracha you make when drinking the coconut water, when served as a mixed drink in the coconut itself?
A. Ben Ish Chai (Pinchas 9) mentions that the dark (or black) melons (avatichim or coconuts) that sometime contain water in them, if one just drinks the water and does not eat the fruit, the brocho is shehakol. However, if he eats the fruit also, he does not need to recite shehakol, since the brocho for the coconut will exempt it. Horav Shlomo Miller's Shlit'a opinion is similar, the haetz recited on the coconut will exempt the shehakol for the water, even if one eats only a bit of it.
The Rov added that sometimes the coconut is served as a pricey inebriating beverage, as is common by the sea resorts. The drink then becomes primary, while the fruit just serves as a decorative jug or glass, that is normally just discarded. Then even if one eats the fruit, no haetz is recited, since the fruit is secondary (tofel) to the drink and would be exempted by the shehakol recited on it.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit'a