Can be prepared in 45 minutes or less.
Makes about 4 cups, serving 2 generously.
In a large heavy saucepan cook the leeks in the butter with salt and pepper to taste, covered, over moderately low heat, stirring occasionally, for 8 to 10 minutes, or until they are softened but not browned. Add the water, the broth, and the potatoes, peeled and cut into 1/2-inch dice, and simmer the mixture, covered, for 20 minutes, or until the potatoes are tender. In a blender purée 1 cup of the soup, stir the puré into the remaining soup with the parsley, and season the soup with salt and pepper.