Meanings
- Any water molecules (H₂O) containing two protium (¹H, hydrogen-1) atoms.
- uncountablechemistryWater in its usual form (as occurs in nature without human intervention), which is mostly of such form.
Synonyms: diprotium monoxide
- uncountablechemistryWater which has had even the usual small amount of deuterium removed (by human intervention): deuterium-depleted water.
Synonyms: diprotium monoxide
- uncountableFoam formed by water and any of various additives, used in firefighting because it floats on flammable liquids lighter than water. (The additives were originally fluorocarbon surfactants but today are increasingly fluorine-free.)
They can be extinguished by carbon dioxide, dry powder, water spray, light water and vaporising liquid
2015, Phil Hughes, Ed Ferrett, Introduction to Health and Safety at Work, →ISBN2 more examples
The light water (AFFF) of the TACR was to be backed up by fluorinated protein foam instead of standard protein foam.
2001, Roger C. Mardon, An Illustrated History of Fire Engines, →ISBN, page 112These fires can be extinguished with water spray, alcohol-resistant foam, light water, vaporising liquids ("Halons"), carbon dioxide and dry powder.
2014, John R. Ridley, Safety at Work, →ISBN, page 504
Synonyms & antonyms
nounWater in its usual form (as occurs in nature without human intervention), which is mostly of such form.
nounWater which has had even the usual small amount of deuterium removed (by human intervention): deuterium-depleted water.
Origin
By reference to atomic weight and atomic mass; more at light hydrogen.
Full word history & related roots →Cite this entry
light water. (n.d.). In WatkinsX Dictionary. Retrieved November 4, 2026, from https://dictionary.watkinsx.com/word/light%20water
“light water.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/light%20water. Accessed November 4, 2026.
WatkinsX Dictionary, s.v. “light water,” accessed November 4, 2026, https://dictionary.watkinsx.com/word/light%20water.
Source: light water on Wiktionary, CC BY-SA 4.0.