(The "8 servings" listinng above should be ignored.... This recipe makes about 10 pounds of marmalade.)
Wash and halve the bitter oranges and lemons. Squeeze out the juice and seeds. Strain the juice into a bowl and tie the pulp, seeds and root ginger together in a piece of muslin or doubled/tripled cheesecloth. Shred peel to the desired thickness and put peel and juice in a pan with the water and the bag of pulp and seeds. Simmer gently for 1 1/2 to 2 hours, or until the peel is quite soft. Remove the bag of pulp (squeeze over the pan as you do) and add the preserved ginger. Measure liquid, add sugar and stir over low heat until dissolved. Boil rapidly to setting point: then can as usual.