When we lift the plastic bucket containing water just above ground level, then the gravitational force starts acting upon the plastic bucket filled with water in the downward direction.
The magnitude of gravitational force of earth acting in the downward direction is equal to the weight of the plastic bucket filled with water. As the muscular force is equal in magnitude and opposite in direction to the magnitude of gravitational force, hence it counteracts with the gravitational pull of the earth, thus not letting the bucket fall down. The two forces are equal in magnitude and opposite in direction. Therefore, the net force on the bucket is zero. Hence, there is no change in its state of motion.
But if the plastic bucket filled with water is lifted up and is not provided with any external force to counteract the gravitational force, then the net force would have been towards the downward direction, and thus the bucket would have been fallen down.