In this Letter we report on a measurement of the Cotton Mouton effect of water vapour. Measurements performed at room temperature (T = 301 K) with a wavelength of 1064 nm gave the value Delta n(u) = (6.67 +/- 0.21) . 10(-15) for the magnetic birefringence at 1 T magnetic field and atmospheric pressure. (C) 2013 Elsevier B.V. All rights reserved.