  Recent experiments on femtosecond pulses in water displayed long distance
propagation analogous to that reported in air. We verify this phenomena
numerically and show that the propagation is dynamic as opposed to self-guided.
Furthermore, we demonstrate that the propagation can be interpreted as due to
dynamic nonlinear X-waves whose robustness and role in long distance
propagation is shown to follow from the interplay between nonlinearity and
chromatic dispersion.
