Wash and drain the rice with room-temperature water.

Place the rice, cinnamon sticks, roughly hand broken into smaller pieces to help infuse their flavor, and 4 cups of water into a large bowl.

Cover the bowl and refrigerate overnight (preferably) or a minimum of 4 hours.

After refrigerating, remove the cinnamon stick pieces. Puree the mixture in two separate batches by adding 1/2 of the rice and 2 cups water at a time into the blender.

Puree until mixture is very smooth and forms a paste-like texture. About 4 minutes.

Using a very fine strainer (or some cheesecloth) pour the blended mixture over a pitcher. Strain out as much liquid as possible, pushing on the solids with a spatula or spoon.

Repeat this process for the entire mixture.

Stir in the milks, vanilla, and 4 cups of water. Stir well.

Add sugar or water according to taste.

Chill and stir before serving over ice.