Water is a liquid.
Water is a transparent and nearly colorless chemical substance that is the main constituent of Earth 's streams , lakes , and oceans , and the fluids of most living organisms . Water strictly refers to the liquid state of that substance , that prevails at standard ambient temperature and pressure ; but it often refers also to its solid state ( ice ) or its gaseous state ( steam or water vapor ) . Evaporation and transpiration contribute to the precipitation over land . However , some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability . Large quantities of water , ice , and steam are used for cooling and heating , in industry and homes .