When a bucket of water is spun in a circle, the water does not spill due to the balance of forces acting on it. The centripetal force, which is directed inward, keeps the water in circular motion, while gravity pulls the water downwards. At the top of the circle, the gravitational force and the tension in the string work together to maintain the water's position. At the bottom, the tension in the string must be sufficient to counteract gravity and provide the necessary centripetal force. Understanding these forces clarifies why the water remains in the bucket during circular motion.