An Evaluation of Water-Water Analytical Potentials in the Region of Low Energy Trifurcated Structures Abstract: Several pairwise additive potentials, frequently used to describe liquid water, and a cooperative potential are examined with respect to their abilities to adequately describe the trifurcated water dimer structures recently reported to be of energies comparable to the best linear structures. All pairwise additive potentials were in error of at least three Kcal/mol while the cooperative model was within one Kcal/mol of the best quantum- mechanical results. It is suggested that, while these pairwise additive potentials may be of considerable use for the description of aqueous water, they should be used with caution where interactions involving individual water molecules or pairs are important.