Specifically, given a reduced potential energy difference between two states i and j defined by ∆u ij (x) = β(U j (x) -U i (x) + P V ), then wherever ∆u ij appears in a reweighting formula such as MBAR or BAR, one can replace it with β(U j (T ij (x)) -U i (x))ln |T ij |, where |T ij | is the Jacobian of the transformation T ij , and we will get valid free energies for the transformation. Specific details of the mathematics and the transformations T ij (x) a function of molecular parameters of water can be found in our previous work. Directly reevaluating these reduced energies would have required (21T × 21P × 6F ) 2 = 7,001,316 evaluations (the 6 comes from 5 sampled plus one unsampled force field). We instead break down the calculation into smaller manageable pieces. For a given pressure, we use all temperatures and water-like force fields to generate the new reduced free energies matrix, i. e. (21 (T) × 1 (P)× 6 (F)) 2 x21 = 15,876 evaluations, to estimate the properties and finally the corresponding mean square error (MSE) overall temperatures at that pressure for the unsampled force field set.