Combine first 7 ingredients in a 3 1/3- or 4-quart slow cooker; stir until blended. Add carrots, chicken and onion; cover and cook on high setting one hour. Reduce heat to low setting and cook 3 to 4 hours.
Stir together flour and cold water until smooth in a small bowl. Gradually stir into slow cooker; cover and cook one more hour.
Pour stew into individual bowls; sprinkle with black pepper, if desired, and top with biscuits.