Using a sharp, firm knife slice a circle around the tip of the coconut. Pour the coconut water into a jug.
Slice the limes into wedges. Strip the mint leaves from half of the stalks. Put 2 wedges of lime with 10 mint leaves and ½ tablespoon of cane sugar in a glass and squash with a cocktail muddler. Add 2 more wedges of lime and some ice cubes. Repeat with another 3 glasses. Divide the rum over the glasses and top up with the fresh coconut water.
