Soak the rice overnight in 3 cups of the water. Add the rice, soaking water and cinnamon to a blender and puree until smooth, 2 or 3 minutes.

Strain into a pitcher through a fine-mesh sieve or several layers of cheesecloth. There should be no grit or large particles in the liquid.

Stir in the remaining 3 cups water, sugar and vanilla. Adjust sugar to taste and serve well chilled over ice.

Garnish with a cinnamon stick.