1. Preheat the oven to 400°. In a large roasting pan, roast the turkey parts for 1 1/2 hours, or until well browned; transfer to a large pot.
2. Set the roasting pan over 2 burners. Add 4 cups of the water and bring to a boil, scraping up the browned bits from the bottom. Add the liquid to the pot.
3. Add the onion, carrot, celery, garlic, salt and several pinches of pepper to the pot along with the remaining 3 quarts of water and bring to a boil. Reduce the heat to moderately low, cover partially and simmer the stock for about 2 1/2 hours. Strain the stock and skim the fat before using or freezing.
Make Ahead: The stock can be refrigerated for 3 days or frozen for 1 month.