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Aims.The goal is to develop a database of rate coefficients for rotational state-to-state transitions in H₂O + H₂O collisions that is suitable for the modeling of energy transfer in nonequilibrium conditions, in which the distribution of rotational states of H₂O deviates from local thermodynamic equilibrium. Methods.A two-temperature model was employed that assumed that although there is no equilibrium between all possible degrees of freedom in the system, the translational and rotational degrees of freedom can be expected to achieve their own equilibria independently, and that they can be approximately characterized by Boltzmann distributions at two different temperatures,T_kinandT_rot. Results.Upon introducing our new parameterization of the collisional rates, taking into account their dependence on bothT_kinandT_rot, we find a change of up to 20% in the H₂O rotational level populations for both ortho and para-H₂O for the part of the cometary coma where the nonequilibrium regime occurs.