In a large bowl combine the mushroom soup, celery soup, water, rice, mushrooms, garlic powder and black pepper. Mix all together. Pour mixture into a 9x13 inch baking dish and spread on bottom.
Lay chicken pieces over soup mixture and sprinkle dry onion soup mix over all. Cover tightly with aluminum foil and bake in the preheated oven for 1 to 1 1/2 hours or until chicken is cooked through and no longer pink inside.