  Energetic, highly-charged oxygen ions, $O^{q+}$ ($q\leq 6$), are copiously
produced upon laser field-induced disassembly of highly-charged water clusters,
$(H_2O)_n$ and $(D_2O)_n$, $n\sim$ 60, that are formed by seeding high-pressure
helium or argon with water vapor. $Ar_n$ clusters (n$\sim$40000) formed under
similar experimental conditions are found undergo disassembly in the Coulomb
explosion regime, with the energies of $Ar^{q+}$ ions showing a $q^2$
dependence. Water clusters, which are argued to be considerably smaller in
size, should also disassemble in the same regime, but the energies of fragment
O$^{q+}$ ions are found to depend linearly on $q$ which, according to
prevailing wisdom, ought to be a signature of hydrodynamic expansion that is
expected of much larger clusters. The implication of these observations on our
understanding of the two cluster explosion regimes, Coulomb explosion and
hydrodynamic expansion, is discussed. Our results indicate that charge state
dependences of ion energy do not constitute an unambiguous experimental
signature of cluster explosion regime.
