Wash the fruit well, dry and peel or grate the rind. Be careful to leave out the white, bitter pith. Chop the orange segments into a rough dice and purée in a blender.
Strain all the juice through a sieve and save a little more than half of the pulp.
In a large pot, pour in the water with the juice, pulp and sugar and heat on medium, stirring till the sugar is dissolved completely.
Throw in the rind and bring the mixture to a boil. Once it is boiling vigorously, reduce to a simmer and leave to bubble away. Don't forget to stir occasionally but for the most part leave it alone.
The marmalade is done when the quantity is less than half and fairly thick. To check, drop a small teaspoonful on a plate and chill in the fridge for 10 minutes. If it sets into semi firm consistency your work is done.
Leave to cool and then pour into clean jars and store in the fridge.
The cooking time is approximate. It would depend on the juiciness of the pulp.