Water vapor is of one of the most important constituents of Venus atmosphere because of its involvement in the formation of cloud, thermal balance and atmospheric chemistry. Water vapour abundance is approximately 30 ppm from ground up to an altitude of approximately 40 km, which is also the limit for Venus clouds. Infrared radiometer (PVOIR) measurements [1, 2, 3] from the 1978–1979 Pioneer Venus Orbiter show that cloud top water vapor has a strong diurnal variation. This variation could be ± 5 ppmv at night for 10 ppmv water vapour content, and daytime values could vary at ± 15 ppmv for values of 90 ppmv. In contrast, 15 Fourier Transform spectrometer (FTS) data from 1983 Venera [3, 4] show that cloud top water vapour abundances is of 7-17 ppmv, with no diurnal variability. Similarly, Earth-based infrared spectroscopy [5] measurements indicate that water vapour mixing ratios is in the range of 0.5 to 40 ppm in the altitude range 62–65 km. Despite the multiple measurements sources, accurate information about water vapour variations is still not available. This variation in the available information may be due to difference in the sounded altitude range, experimental and modeling errors. © 2019 URSI. All rights reserved.