text: It depends what you mean by weigh less.\n\n* If you are referring to its density, cooling it below 0°C at Standard Temperature and Pressure will freeze it, and reduce its density (boiling it above 100 C again will have the same effect).\n\n* If you are just referreing to the weigh (and not the mass), taking your water to a place with a lower gravitational field than earth's field (eg the moon, or in a space station in orbit) will make it "weigh less"; since P = m g. Where P is the weigh vector and g is the gravitational field.\n\nBeware: heating it to water vapour (or freezing it to ice) will NOT reduce its weight, just its density.