In order to train the short-range interactions (both the isotropic and the anisotropic parts), we built a training set containing the interaction energies of small water clusters up to 5 molecules. The water clusters in the training set were generated with the following procedure: First, path-integral molecular dynamics (PIMD) simulations 118 with 32 beads were run at ambient condition (300K, 1bar) for both bulk water (with 1024 molecules) and small water clusters (with 2-12 molecules). From these PIMD trajectories, we first picked a central molecule, then built the cluster by including all the molecules within 4Å from the central molecule. The size of the cluster was limited to five molecules, representing one central molecule with its first solvation shell (i.e., the four molecules hydrogen bonded to the central molecule directly). In total, we obtained a training set consisting of 1421 dimers, 2214 trimers, 2090 tetramers, and 6647 pentamers from cluster trajectories, and 2585 pentamers from the bulk trajectory. All PIMD simulations were conducted using OpenMM-7 program 119 and q-tip4p/f force field. C. Testing Set While we trained the models using clusters no larger than pentamer, we tested their transferability by computing the root mean squared deviations (RMSD) of the predicted interaction energies for octamers.