Immediately after removing meat from a roasting pan or other pan, drain off the drippings, reserving 2 tablespoons. Sprinkle the flour over drippings; cook and stir over medium heat until brown. Gradually stir in milk, whisking with a fork to scrape up all of the meaty bits from the pan, then gradually whisk in the water. Increase the heat to medium-high, and cook, stirring constantly, until the gravy thickens, about 10 minutes. Taste, and season with salt and pepper.