1. Place the washed oranges in a heavy-based saucepan with the water. Put a plate on top to prevent them bobbing over the surface of the water. Cover with the lid of the saucepan and simmer for approximately 2 hours or until the oranges are soft. Cool and drain, reserving the water.
2. Preheat the oven to 180°C (350°F), Gas mark 4. Place the sugar in an ovenproof bowl and put in the oven for about 15 minutes to warm through.
3. Place a chopping board on a large baking tray to catch any juice from the oranges.
Cut the oranges in half and scoop out the soft centres, then slice the zest into slices approximately 3–5mm (1/8–1/4in) thick (or thicker if you prefer).
4. Place the pulp with the pips into a muslin bag (or a clean ‘J’ cloth or something similar) and pour any escaped juice into a large, wide, stainless steel saucepan, along with the reserved cooking water and the sliced oranges. Bring to the boil, then add the warm sugar. Stir over a high heat until all the sugar is dissolved. Boil rapidly for about 20 minutes until setting point is reached (see opposite). If the marmalade hasn’t set, boil for a minute or so longer and test again.
5. Remove the pan from the heat, pot into sterilised jars and cover with lids or jam covers while still hot.