Heat the butter in a large saucepan over medium heat, and cook and stir the carrots and onion until the carrots begin to soften and the onion is translucent, about 5 minutes. Pour in the chicken broth and water, and bring the mixture to a boil. Stir in the couscous, mixing well to avoid lumps, cover, and remove from the heat. Let the couscous stand covered until the water is absorbed, about 5 minutes.
