In a first optimization test, we trained the optimized water model according to a purely bottom-up approach to reproduce the experimental RDFs (g OO , g OH and g HH ) of water at the standard conditions of 298 K and 1 bar. At every iteration, Swarm-CG tests new parameters in the attempt to minimize the discrepancy between the g OO , g OH and g HH obtained from the model and the experimental ones in standard conditions. The obtained results are presented in Figure . A comparison with other popular three-site water models of the same type (OPC3, 31 TIP3P-FB, 24 SPC, 18 SPCE, 32 SPCEb 33 and TIP3P ) is also provided. A summary of the parameters for these models can be found in Table of the Supplementary Information.