what is the difference between heavy water and hard water ?
Heavy water:Heavy water is water which contains a higher proportion than normal of the isotope deuterium, as deuterium oxide, D2O or ²H2O, or as deuterium protium oxide, HDO or ¹H²HO. Its physical and chemical properties are somewhat similar to those of water, H2O. Heavy water may contain as much as 100% D2O, and usually the term refers to water which is highly enriched in deuterium. The isotopic substitution with deuterium alters the bond energy of the hydrogen-oxygen bond in water, altering the physical, chemical, and especially biological properties of the pure or highly-enriched substance to a larger degree than is found in most isotope-substituted chemical compounds.