  We explore from a theoretical perspective the dynamical response of small
water clusters, (H$_2$O)$_n$H$_3$O$^+$ with $n=1,2,3$, to a short laser pulse
for various frequencies, from infrared (IR) to ultra-violet (UV) and
intensities (from $6\times10^{13}$ W/cm$^2$ to $5\times10^{14}$ W/cm$^2$). To
that end, we use time-dependent local-density approximation for the electrons,
coupled to molecular dynamics for the atomic cores (TDLDA-MD). The
local-density approximation is augmented by a self-interaction correction (SIC)
to allow for a correct description of electron emission. For IR frequencies, we
see a direct coupling of the laser field to the very light H$^+$ ions in the
clusters. Resonant coupling (in the UV) and/or higher intensities lead to fast
ionization with subsequent Coulomb explosion. The stability against Coulomb
pressure increases with system size. Excitation to lower ionization stages
induced strong ionic vibrations. These maintain rather harmonic pattern in
spite of the sizeable amplitudes (often 10% of the bond length).
