Thinly slice lemons, grapefruit, and oranges, removing seeds.

Combine sliced citrus fruits and water in a large bowl.

Cover and refrigerate overnight.

Transfer the mixture to a Dutch oven.

Bring to a boil.

Reduce heat and simmer, uncovered, for 10-15 minutes or until fruit is tender.

Stir in sugar.

Bring to a boil again.

Cook and stir for 45-55 minutes or until thickened, stirring frequently.

Remove from heat.

Skim off any foam from the surface.

Carefully ladle the hot marmalade mixture into hot, sterilized half-pint jars, leaving 1/4-inch headspace.

Remove any air bubbles.

Wipe the rims of the jars and adjust lids.

Process for 5 minutes in a boiling-water canner.