In the originally published version of this article, we incorrectly reported the total pressure applied to the full simulation cell (P sim ) as the pressure experienced in the confined region of water. This is erroneous as the confinement pressure is higher and is approximated as P conf = P sim * z/w, where z is the z-dimension of the simulation box (assuming an x-y confinement plane) while w is the confinement width1,2,3. Further details on estimating the pressure are in the updated Methods section. This correction does not affect the simulations or the observed phase behaviour, but it scales the pressure values by approximately a factor of 3. The onset of superionic behaviour occurs at 10.5–12 GPa rather than 3.5–4 GPa. Qualitative conclusions of the work remain unchanged. We also make an additional clarifying point that the statement on the impact of quantum nuclear effects on the phase transition only concerns the solid phases.