As outlined in our paper, we developed a model which is able to explain all recorded THz pump–probe data at 12.3 THz in the static water cell as well as in the liquid jet. The model includes an instantaneous temperature-dependent response by an acoustic phonon, an inherent non-linear response of water, and a slower thermal response. The order of magnitude of the non-linear contributions agrees with previous experimental results by us² and other groups (see ref. 32, 33 and 35 in ref. 1) as well as with simulations², which predict an enhanced non-linear response of water in the frequency range of the libration.