Light water or Lightwater may refer to:

Science

• Deuterium-depleted water, which has a lower concentration of deuterium than occurs naturally on Earth
• Water, especially water that is not heavy water
  • Water, the coolant in a light-water reactor type of nuclear reactor

Other uses

• Lightwater, a town in Surrey, England

See also

• Semiheavy water, the result of replacing one of the protium in light water to deuterium
• Heavy water, a form of water that contains a larger than normal amount of the hydrogen isotope deuterium