On Earth, deuterated water, HDO, occurs naturally in normal water at a proportion of about 1 molecule in 3,200. This means that 1 in 6,400 hydrogen atoms is deuterium, which is 1 part in 3,200 by weight (hydrogen weight). The HDO may be separated from normal water by distillation or electrolysis and also by various chemical exchange processes, all of which exploit a kinetic isotope effect. With the partial enrichment also occurring in natural bodies of water under particular evaporation conditions. (For more information about the isotopic distribution of deuterium in water, see Vienna Standard Mean Ocean Water.)