  It is suggested that the dynamics of liquid water has a component consisting
of O^{-2z} (oxygen) anions and H^{+z} (hydrogen) cations, where z is a (small)
reduced effective electron charge. Such a model may apply to other similar
liquids. The eigenmodes of density oscillations are derived for such a
two-species ionic plasma, included the sound waves, and the dielectric function
is calculated. The plasmons may contribute to the elementary excitations in a
model introduced recently for the thermodynamics of liquids. It is shown that
the sound anomaly in water can be understood on the basis of this model. The
results are generalized to an asymmetric short-range interaction between the
ionic species as well as to a multi-component plasma, and the structure factor
is calculated.
