Cut oranges and lemon into thin slices or small dices, depending on your preference. Remove any seeds.
Get thin-skinned fruit, if possible. If the pith is too thick, remove rind from fruit and slice off the majority of the pith.
Alternatively, roughly chop oranges and lemon and pulse in a food processor until of the desired consistency.
Add fruit and water to a large, non-reactive Dutch oven. Bring to a boil, then reduce heat and simmer for 5 minutes.
Remove from heat and stir in sugar until it dissolves. Cover at let rest for 24 hours at room temperature.
Place small plates in the freezer.
Bring fruit to a boil over medium-high heat and then reduce to a simmer. Cook for approximately 1 to 1 1/2 hours until the temperature of the marmalade reaches between 220 and 222 degrees.
To test for the gel point, place a small dollop of marmalade on one of the plates in the freezer for 1 to 2 minutes.
When the marmalade reaches the gel point, ladle into hot, sterilized jars leaving 1/4-inch headspace. Run plastic knife or spatula between marmalade and jar to release any air bubbles. Clean rim and threads of jar with damp cloth.
Process in a boiling water bath for 10 minutes. Makes 4 half-pints.