Deuterium-depleted water (DDW) is water that has a lower concentration of deuterium than occurs naturally at sea level on Earth. Natural water typically contains approximately 150 parts per million of deuterium, while DDW refers to water with deuterium concentrations below that level. DDW has also been described in scientific literature as “light water” or “protium water,” although “light water” is also used in nuclear engineering to refer to ordinary water used in light-water reactors.
Chemistry Deuterium-depleted water has less deuterium (2H) than occurs in nature at sea level. Deuterium is a naturally occurring, stable (non-radioactive) isotope of hydrogen with a nucleus consisting of one proton and one neutron. A nucleus of normal hydrogen (protium, 1H) consists of one proton only, and no neutron. Deuterium therefore has about twice the atomic mass as 1H. Heavy water molecules contain two deuteriums instead of two 1H atoms. Deuterium has an amount fraction of 0.00015574, or about 156 deuterium atoms per million hydrogen atoms. Production of heavy water involves isolating and removing deuterium-containing isotopologues within natural water. The by-product of this process is DDW. DDW may be produced through isotope-separation processes that reduce the concentration of deuterium-containing water molecules, including distillation and catalytic-exchange methods. The isotopic composition of natural water varies by geography and climate. In general, precipitation and surface waters tend to become more depleted in deuterium with increasing distance from the ocean, increasing distance from the equator, and higher elevation. This variation is used in hydrology and isotope geochemistry to compare water samples against international reference standards. Vienna Standard Mean Ocean Water (VSMOW) is an international reference standard that represents the isotopic composition of ocean water. In VSMOW, deuterium occurs at a concentration of 155.76 ppm. Standard Light Antarctic Precipitation (SLAP), a reference standard based on Antarctic precipitation, represents a more deuterium-depleted natural water standard, with a deuterium concentration of 89.02 ppm. Snow and glacial meltwater can have lower deuterium concentrations than seawater, reflecting isotopic variation associated with altitude, latitude, and hydrological conditions. The weight quantities of isotopologues in natural water are calculated based on data collected using molecular spectroscopy. The following table compares the calculated mass content of water isotopologues in VSMOW and SLAP. It includes both oxygen-isotope variants and deuterium-bearing isotopologues, with the latter being most directly relevant to deuterium-depleted water.
In this comparison, VSMOW contains approximately 0.329 g/kg of deuterium-bearing isotopologues, compared with approximately 0.188 g/kg in SLAP. This difference reflects the lower deuterium content of SLAP relative to the ocean-water standard. Most of the total mass of heavy isotopologues shown in the table comes from ¹H₂¹⁸O, a water molecule containing light hydrogen and oxygen-18, rather than from deuterium-bearing water molecules.
Biological properties of the deuterium content in water Early biological research found that heavy water could inhibit growth in experimental systems. Later DDW research has examined cellular, animal, metabolic, and cancer-related models, but much of the evidence remains preclinical or heterogeneous. A 2024 scoping review described nutritional deuterium depletion as an emerging research area involving DDW, diet, metabolism, and health, while noting that additional randomized controlled trials are needed.
Production methods Deuterium-depleted water can be produced in laboratory and industrial settings. Reported production methods include electrolysis, low-temperature vacuum rectification, seawater desalination, Girdler sulfide process, and catalytic exchange.
Commercial production Commercially produced deuterium-depleted water is sold as bottled water and as concentrated products for dilution. Some market reports identify Litewater Scientific, Preventa, and Qlarivia, and among companies active in the DDW market.
Health claims and criticism In 2020, Harriet Hall wrote in Skeptical Inquirer that most DDW studies she reviewed were preclinical and that the limited human studies available at the time did not establish human efficacy. More recent reviews have summarized DDW research in cellular, animal, metabolic, and cancer-related models, while noting limitations in study design and the need for stronger clinical evidence. DDW has been studied in relation to cancer, diabetes, metabolism, oxidative stress, and other biological processes. However, much of the evidence remains preclinical or heterogeneous, and claims concerning disease treatment should not be presented as established medical consensus. For example, one preclinical study reported DDW-related effects on GLUT4 translocation and blood-glucose concentration in diabetic rats.
See also Kinetic isotope effect Light water (disambiguation) Properties of water
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