Estimating the exact entropy of water molecules on Pt(111) is challenging. A lower bound can be obtained by considering the standard entropy of solid water (ice) which is estimated to be ≈ 0.12 eV. In this scenario water molecules at the interface are ice-like and are not free to move. Considering that previous experimental and theoretical studies have shown that water retains some mobility at the Pt(111) interface this view will underestimate the entropy of water at the interface. The opposite argument would be to consider that water molecules are free to move and rotate, leading to the same entropy as in the liquid phase, likely overestimating the entropy. A more accurate approach might be to make use of the work from Campbell and Sellers 97 who studied the entropy of adsorbate molecules on various surfaces and found a linear dependence between the entropy of the adsorbate and its gaseous equivalent. Using their formula we find a value of 0.38 eV, right between the two extremes.