In a medium saucepan, combine cranberries, orange zest, cinnamon, orange juice and brown sugar. Add enough water to cover then bring to the boil over high heat. Immediately reduce heat then simmer for about 1 hour, or until the sauce has thickened. Taste for sweetness then adjust with additional sugar if necessary. You cannot overcook, so continue cooking until you have a good thick consistency. Let mixture cool, then refrigerate in a covered container.