How is heavy water different from normal water

About 70 per cent of the Earth's surface is covered with water. Heavy water is also water, but it contains a higher proportion of the hydrogen isotope - deuterium. Two hydrogen atoms and one oxygen atom makes a water molecule ... It is this extra neutron that adds to the weight of the atom, which makes it heavier.

Physical properties to distinguish water from heavy water: Heavy water is 10.6% denser than ordinary water. One of the few ways to demonstrate heavy water's physically different properties without equipment is to freeze a sample and drop it into normal water (it sinks).