Place a small plate or glass dish in the freezer. You will use this later to test the viscosity of the marmalade.

Thoroughly wash the oranges and lemon. Thinly slice oranges and lemon, removing seeds as you go. Stack the slices and quarter them. In a large non-reactive pot, combine citrus slices and water. Place the pot over high heat and bring to a boil. Once it comes to a boil, reduce heat, cover and simmer for 30 minutes. Uncover and let simmer an additional 15 minutes or until citrus is very soft, stirring occasionally.

Raise heat and mixture to a boil. Add sugar to citrus mixture and mix until well combined. Let boil until mixture reaches 223ºF on a candy thermometer, about 30 minutes. Keep a close eye on the marmalade. The mixture should darken in color. Test the doneness of the marmalade by placing a small amount of the marmalade on the chilled plate and letting it sit for 30 second. The mixture should turn into a soft gel and move slightly. If it is runny and thin, let it continue to boil until it reaches desired consistency.

The marmalade is now ready for canning.