Semiheavy water
Semiheavy water (HDO or HOD) is a naturally occurring chemical variant of water. Other variants include heavy water (D2O), and H2O. It shares most of its properties with common water (1H2O), with its distinguishing feature being a single hydrogen atom per water molecule being of the heavier isotope deuterium (2H or D), as opposed to the far more common protium (1H).