 Deuterium-depleted water

Deuterium-depleted water (DDW) is water that has a lower concentration of deuterium, a stable isotope of hydrogen, compared to regular water (H2O). In regular water, most of the hydrogen atoms are protium (the most common isotope of hydrogen, with no neutrons), but a small percentage (approximately 0.0156%) are deuterium (D), which has one neutron in addition to the proton.