2 cups boiling water
2 cups long-grain white rice
1 stick cinnamon, crushed, plus sticks for garnish
2 cups unsweetened coconut water
Cheesecloth, for straining
1 cup unsweetened coconut milk
2⁄3 cup sugar
1 pinch kosher salt
Stir water, rice, and cinnamon in a bowl; cover and let sit at room temperature overnight.
The next day, transfer rice mixture to a blender. Add coconut water; purée until smooth, 3–4 minutes. Strain through a cheesecloth-lined sieve into a pitcher; cover and chill until ready to serve.
Heat coconut milk, sugar, and salt in a 2-qt. saucepan over low; cook until sugar dissolves, about 3 minutes. Let milk cool; stir into rice mixture. Serve in ice-filled glasses; grate fresh cinnamon over top and drop sticks into glasses.