Mix 2 cups cold water and flour until smooth. Add cold water mixture to the drippings. Whisk until all lumps have been dissolved.
Keep 1 cup cold water close by to add, just in case gravy becomes thick. Turn heat to medium-high. Bring gravy mixture to a boil, stirring constantly. As mixture boils, it turns a slightly darker color; continue to stir.
Salt and pepper to taste; serve hot.
Gravy too thick? Add cold water a little at a time until it thins out. Gravy will thicken a little as it cools. If it is too thick while it is cooking it may become lumpy. If you do have lumpy gravy, strain out the lumps before serving.
Gravy too thin? Boil a little longer until it thickens. If it is still too thin, mix 2 parts cold water to one part flour. Stir quickly until all lumps have been dissolved and add to gravy, stirring constantly.