Temporal evolution of the pebble metallicity in a large protoplanetary disc (R₁ = 112 AU) at 5 AU (outside of the water ice line, blue lines) and at 0.5 AU (inside of the water ice line, red lines) for two different combinations of the viscosity coefficient (α) and the turbulent diffusion coefficient (δ). Water vapour released at the passage of the water ice line is included in the metallicity at 0.5 AU. The instantaneous position of the water ice line is indicated above the plots. The high viscous heating in the case α = δ = 10⁻³ (bottom) pushes the ice line out, while the lower speed of the gas allows for a much bigger pileup of water vapour inside of the water ice line.