Rosseland mean opacity for micrometre-sized dust grains for the different water-to-silicate ratios. For low temperatures the discs with more water have a larger opacity, because the reflection and absorption parameters for water ice grains yield a higher opacity than for silicate grains. At the water ice line (grey area) ice grains sublimate, causing a drop in opacity. This drop is larger if the water fraction in the disc is high. The opacity at higher temperatures is larger for discs with more silicates, because more silicate grains are available that can contribute to the opacity. The values of opacity here are calculated for a disc with a total metallicity of Z_dust = 0.5% in dust grains.