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Heavy water (deuterium oxide (2H 2O) or D 2O) is a form of water that contains a larger than normal amount of the hydrogen isotope deuterium (2H or D, also known as heavy hydrogen), rather than the common hydrogen-1 isotope (1H or H, also called protium) that makes up most of the hydrogen in regular water.
Best Answer: Water consists of 2 hydrogen atoms bonded to an oxygen atom. In heavy water either one or both of the hydrogen atoms have been replaced by deuterium. Deuterium is an isotope of hydrogen, it contains the same number of protons (1) and still has one electron, but it has a neutron.