Editing Heavy water (section)

===Semiheavy water===
[[File:Semiheavy water.svg|thumb|right|120px|Structure of semiheavy water]]
[[Semiheavy water]], HDO, exists whenever there is water with light hydrogen (protium, {{chem|1|H}}) and deuterium (D or {{chem|2|H}}) in the mix. This is because hydrogen atoms ({{sup|1}}H and {{sup|2}}H) are rapidly exchanged between water molecules. Water containing 50% {{chem|1|H}} and 50% {{chem|2|H}} in its hydrogen, is actually about 50% HDO and 25% each of {{chem|H|2|O}} and {{chem|D|2|O}}, in [[dynamic equilibrium]].
In normal water, about 1 molecule in 3,200 is HDO (one hydrogen in 6,400 is {{chem|2|H}}), and heavy water molecules ({{chem|D|2|O}}) only occur in a proportion of about 1 molecule in 41 million (i.e. one in 6,400{{sup|2}}){{Citation needed|reason=the statistical reasoning here is very clear to me. There are three different numbers thrown around, 1/6400,1/20mil,1/41mill. Their statistics aren't cited and their logic isn't foolproof, as can be seen by the fact I'm complaining about it.|date=August 2023}}. Thus semiheavy water molecules are far more common than "pure" (homoisotopic) heavy water molecules.