Place the water in a large pot, bring to a boil. Add the rice and the cinnamon stick, mix well. Bring to a boil again and cook until the rice is translucent but not cooked through. Add the milk and bring to a boil again. When the rice is very soft, add the sugar and stir to dissolve. When it boils again add the cornstarch previously dissolved in the 1/4 cup water. Cook stirring often until it thickens.