Place rice in a sieve and rinse under cold running water. Blend rice with 250ml (1 cup) water and cinnamon in a blender, then strain through a muslin cloth or very fine sieve into a jug. Repeat straining mixture four times until liquid is white and powder-free.
Add sugar to taste and stir until dissolved. Add remaining 750ml (3 cups) water and refrigerate. Serve horchata cold.
Add sugar to taste and stir until dissolved. Add remaining 750ml (3 cups) water and refrigerate. Serve horchata cold.