"coconut water (or juice) is the thin liquid found naturally inside young green coconuts —not to be confused with creamier coconut milk, which is made from the white flesh of older coconuts.
coconut water provides potassium (about 600 milligrams per cup, more than a banana), along with some calcium, magnesium, sodium, and sugar.
it’s debatable whether the saturated fat in coconut milk is bad for you, but coconut water has no fat to worry about. and it’s far lower in calories than coconut milk (about 45 versus 500 per cup).
because coconut water has the same electrolyte balance as blood (it’s "isotonic"), it has been called "the fluid of life." during world war ii, it was used as a substitute for intravenous plasma. http://www.berkeleywellness.com/html/wl/2007/wlaskexperts1207.html