Energy of hydrogen bonds vs. kinetic energy of water molecules
It looks like they calculated the average thermal energy of water molecules, which by classical equipartition theorem is $3RT/2$ kJ mol$^{-1}$. This works out at approx 4 kJ mol$^{-1}$ at 40 C. This amount of energy includes translational, vibrational and rotational energy. The vibrational quanta are large in water and almost all molecules will have only zero point vibrational energy. Rotational quanta are smaller and many will be excited at these temperatures. The smallest rotational quantum value for water is approx 0.2 kJ mol$^{-1}$ the next 6 times larger and the next 12 times (increasing as $J(J+1)$ for quantum number J) so a few rotational levels will be populated. Energy will flow between translation and rotations as random collisions occur between molecules of water. A full calculation involves using the partition functions. Calculating these and their contribution to heat capacity is treated in most undergraduate phys. chem. textbooks.