1. Combine the sliced oranges and water in a large pot.
2. Bring to a boil and cook rapidly for 20 minutes or until tender.
3. Add the sugar and cook over low heat, stirring until the sugar dissolves.
4. Turn up the heat and boil rapidly about 40 minutes until the bubbling stops and the fruit becomes opaque, or until a candy thermometer reads 220°F.
5. Remove from the heat, skim the foam from the surface and let cool for 5 minutes.
6. Stir to distribute the fruit throughout the syrup. Cool completely.
Note: The marmalade can be stored in the refrigerator for 5 days.Serving Size: 1 tablespoon