Gently muddle five mint leaves, the sugar, the lime juice and a few pieces of expressed lime. The goal is not to pulverize the leaves into tiny bits; instead, gently bruise them to release their essence.
Fill the glass halfway with ice, then add the coconut water.
Stir clockwise for about 30 seconds to fully combine and dissolve the sugar. Alternatively, you can dump the contents into a shaker and give it a good shake.
Add ice to the top, then fill the rest of the way with seltzer.
Garnish with a wheel of lime and a sprig of mint.