  We present the first set of rate coefficients for the rotational excitation
of the 7 lowest levels of hydrogen fluoride (HF) induced by collision with
water molecules, the dominant collider in cometary comas, in the 5-150 K
temperature range. The calculations are performed with a quantum statistical
approach from an accurate rigid rotor ab initio interaction potential. Rate
coefficients for excitation of HF by electron-impact are also computed, within
the Born approximation, in the 10-10,000 K temperature range. These rate
coefficients are then used in a simplified non-local thermodynamic equilibrium
(non-LTE) model of a cometary coma that also includes solar radiative pumping
and radiative decay. We investigate the range of H2O densities that lead to
non-LTE populations of the rotational levels of HF. We show that to describe
the excitation of HF in comets, considering collisions with both water
molecules and electrons is needed as a result of the large dipole of HF.
