Plain coconut water is literally just the water on the inside of a coconut. So if you can get coconuts at your grocery store you can get coconut water. I also found this recipe on how to extract and flavor the water: http://www.eatnapplay.net/2013/03/04/make-your-own-coconut-water/.
About Celebrity Solstice. Celebrity Solstice is a large ship, carrying 2850 passengers and 1246 crew, and sails from Sydney, Australia and Auckland, New Zealand.
June Solstice: Longest and Shortest Day of the Year. The June solstice is the Summer Solstice in the Northern Hemisphere and the Winter Solstice the Southern Hemisphere. The date varies between June 20 and June 22.