Deuterium depleted water, also known as DDW, is a type of water that has a lower concentration of deuterium than regular water. Deuterium is a heavy isotope of hydrogen, and while it is not harmful to human health, high concentrations of deuterium in water have been linked to negative health effects in some studies. DDW has been touted as a potential health elixir, with some claiming that it can help with everything from weight loss to cancer prevention.