Water model. The DE water model was fit to reproduce six experimentally determined properties over a wide range of temperatures and pressures. The reference values of the properties: density, heat of vapourisation, thermal expansion coefficient, isothermal compressibility, isobaric heat capacity and dielectric constant are identical to those used in previous work fitting the TIP4P-FB and TIP3P-FB models . Due to computational constraints however we only included 12 data points in total distributed between temperatures of 249.15K-373.15 K and the full pressure range, see the Supporting Data for the complete set of reference data used. The ForceBalance control file is provided in the Supporting Data but briefly the model was held rigid at the TIP4P-FB geometry via bond and angle constraints. The liquid simulations started with 1 ns of equilibration followed by a 8 ns production using a 1 fs timestep. Gas phase simulations were equilibrated for 0.5 ns before a production simulation of 5 ns using a 0.5 fs time step.