First, in a microwave-safe bowl heat the milk in the microwave until it reaches 100 degrees F, about 1-2 minutes. Pour the rice into the hot milk and let it sit for 30 minutes.
Then, transfer the rice mixture to a blender canister. Add 2 cups of the water, cinnamon, and vanilla. Blend on high for 2-3 minutes, or until all the rice is finely chopped and blended.
Next, place a fine mesh strainer over a large pitcher (at least 3 quarts). Pour the mixture through the strainer into the pitcher. Discard what's left in the strainer.
Add the remaining 10 cups of water and sugar, stir to combine. Finally, serve over ice.
FOR HORCHATA FRAPPUCCINO:
In the canister of a blender, add the Horchata and ice cream. Blend until smooth, about 3-5 pulses. Pour into a tall glass and garnish with whipped cream and ground cinnamon.