  We present an accurate free-energy functional for liquid water written in
terms of a set of effective potential fields in which fictitious noninteracting
water molecules move. The functional contains an \emph{exact} expression of the
entropy of noninteracting molecules and thus provides an ideal starting point
for the inclusion of complex inter-molecular interactions which depend on the
\emph{orientation} of the interacting molecules. We show how an excess
free-energy functional can be constructed to reproduce the following properties
of water: the dielectric response; the experimental site-site correlation
functions; the surface tension; the bulk modulus of the liquid and the
variation of this modulus with pressure; the density of the liquid and the
vapor phase; and liquid-vapor coexistence. As a demonstration, we present
results for the application of this theory to the behavior of liquid water in a
parallel plate capacitor. In particular, we make predictions for the dielectric
response of water in the nonlinear regime, finding excellent agreement with
known data.
