Soak rice, almonds and 1 1/2 cups water in blender overnight. Blend until smooth. While blending, add cinnamon, sugar and vanilla. Line sieve with cheesecloth and put on top of a large pitcher, pour contents of blender slowly through, gather ends of cheesecloth and squeeze out excess. Thin out with the additional water, adding more or less to your taste.
Serve immediately over ice.