Final deuteration of water ice (at t > 10⁶ yr: representative of a typical molecular cloud age) as function of visual extinction for three values of temperatures: 10 (red), 15 (blue), 20 (green) K, using a total density of 10⁴ cm^-3, an H₂ opr of 3 × 10^-6 and including the variation of all other input parameters. The vertical line refers to the A_V threshold of water ice observed by Whittet et al. (1988). Hatched boxes refer to water deuteration observed by Coutens et al. (2012) towards IRAS 16293.