In a medium saucepan over medium heat, combine water, milk, sugar and cinnamon. Bring to a boil and remove from heat. Remove cinnamon stick. In another saucepan, melt butter over medium heat. Allow it to bubble, but not to brown. Reduce the heat to low and stir in the semolina, a little at a time, until mixture is thick and smooth. Allow it to brown slightly, then stir in the milk mixture, a little at a time. Continue to stir until mixture has progressed from creamy to thick. Place halva in a gelatin mold or glass dish. Serve warm or cold.