Heavy water is a form of water in which hydrogen atoms are all deuterium rather than the common hydrogen-1 isotope that makes up most of the hydrogen in normal water. Heavy water has different physical properties from regular water, such as being 10.6% denser and having a higher melting point. Heavy water is less dissociated at a given temperature, and it does not have the slightly blue color of regular water. It can taste slightly sweeter than regular water, though not to a significant degree.
Heavy water
