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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.
Heavy water has a deuterium atom with two oxygen atoms bonded to it. Tritium, H+3 , is radioactive. H2O usually is electrically neutral, but if the hydrogen atom is deuterium, and the water molecule is D2O, the electrical charge of the heavy water is +1, until an electron fills the shell in the d orbital of the hydrogen atom.