  Can we avoid molecular dynamics simulations to estimate the electrostatic
interaction between charged objects separated by a nanometric distance in
water? To answer this question, we develop a continuous model for the
dielectric properties of water based on a functional of the polarization. A
phenomenological Landau-Ginzburg Hamiltonian for the electrostatic energy of
water is parameterized to capture the dipolar correlations in the fluid at the
nanometric scale. We show that in this framework, the effective interactions of
simple objects such as point charges are analytically tractable. In particular,
the derivation of the interaction energy between a solvated charge and a
surface can be reduced to a system of linear equations of electrostatic
potentials and analytically solved. This approach could thus give access in few
calculation lines to data that necessitate long and costly simulations.
