From their atomic composition, water molecules in ice ideally arrange in a tetrahedral coordination made of four hydrogen bonds per molecule. In liquid water, entropic effects bend, stretch, break and reform hydrogen bonds such that the average number of H-bonds per molecule is slightly less than 4 (∼3.8) at near ambient conditions . This average number h is plotted in Fig. , where the gray boxes indicate the estimated discrepancy among various experimental methods at the simulated temperature . Our observations, and those of others 136 , suggest that the computation of h is relatively insensitive to changes in temperature, with a small deviation of approximately 0.1 for every 10 K increase.