Heat the oven to 475°F. Using a sharp knife, cut an “X” about 1 inch long through the shell on the flat side of each chestnut. Measure out about 2 feet of aluminum foil and set it over a baking sheet. Place the chestnuts in the middle of the foil in a single layer. Bring the shorter sides of the foil up so they kiss. Crimp the longer sides over to create a seal. Leave a 1-inch hole at the top to create a vent. Pour the water into the vent and cook the foil pouch in the oven for 5 minutes. Lower the oven temperature to 375°F, carefully pull the foil down all the way to expose the chestnuts, and continue to cook until tender, about 25 minutes more. Peel when cool enough to handle.