Mix in blender 3-5 minutes until smooth and not gritty. Add 2 cups of water and blend again for a few seconds. Place a sieve, lined with 3 layers of damp cheesecloth, over a bowl. Pour in rice mixture a little at a time, stirring, then twist cheesecloth to squeeze out remaining liquid. Add 2 cups of water or to desired consistency and sugar to taste. Cover and refrigerate. Serve in tall glass over ice.