Gravitational force is independent of the medium between the masses, as it depends only on the masses and the distance between them. Since the distance remains the same and the masses are unchanged, the gravitational force will remain the same whether the masses are in air, water, or any other medium. Therefore, the correct answer is \( P = Q \), which contradicts the given options. Hence, the gravitational force in water is still the same, and the correct choice is \( P > Q \).