Preheat the oven to 110°C. Wash the pork belly and pat dry. Place in a heavy baking dish, skin down, and add the water.
Spread a thin film of sauce evenly over the pork and sprinkle with the garlic–ginger mixture. Cover loosely with aluminium foil.
Over the next 4 hours, the pork will rise like a soufflé, releasing some of its fat. Eventually it will collapse into a gelatinous, soft texture, redolent of Chinese flavours.
Serve the pork belly with a salad of thinly sliced cabbage dressed with a little balsamic vinegar and a drizzle of the pork cooking juices. Cucumber is also nice and refreshing, and steamed rice makes a good starch accompaniment to mop up the juices.