Place ice in a blender and pour in coconut water; add cherries, watermelon cubes, and sweetener. Cover and blend until slushy, about 1 minute. Pour into 2 glasses to serve.
A variety of fruit can be added to this recipe such as blueberries, strawberries, melon, etc. Blackberries and raspberries are not recommended because of the seeds. A variety of sweeteners can be used for this recipe, or none at all. Some possibilities would be cane sugar, honey, Splenda(R), or agave.