Preheat the oven to 400 °F (200 °C).
Prepare pork belly: Dry the skin carefully, for example, by means of suitable kitchen paper. Using a very sharp knife, make shallow, parallel cuts on the top surface of the meat. Rub the salt into scored skin of the pork belly.
Pour water into the baking dish and place in it the meat skin side up.
Roast the meat uncovered for 30 minutes at a high temperature of around 400 °F (200 °C) until the surface is golden brown.
Reduce the oven temperature to 300 °F (150 °C) and bake for another 2 hours.
Occasionally pour the juices from the bottom of the pan over the meat (I baste the pork belly myself every 20 minutes). You will be rewarded with crispy skin and tender meat even with so little work.
Remove the meat from the oven and let rest for 5 to 10 minutes.
Cut into crosswise slices about 1 inch (2.5 cm) wide and serve.