The values of water pressure will be changed to be consistent with the new international temperature scale (ITS-90, International Temperature Scale of 1990) announced in 1990. In the work reported, the formulations and changes of water vapour pressure due to adoption of ITS-90 are discussed. ITS-90 has lower values than those of the International Practical Temperature Scale of 1968 (IPTS-68), for example, ITS-90 is lower by 12.65 mK at 50 deg C, and lower by 26.1 mK at 100 deg C compared to IPTS-68. Water vapour pressures calculated with the formulation introduced by Wexler in 1976 are lower by 7.75 Pa at 50 deg C, and lower by 93.4 Pa at 100 deg C than that of ITS-68.

KEYWORDS: water vapour, pressure, calculating, temperature, thermodynamics, properties