  We determine the structure of the hydrodynamics with conserved current, using
the gauge/gravity duality of charged black-hole background. It turns out that
even in the presence of the external electromagnetic field at the boundary,
bulk Einstein equation is equivalent to the boundary conservation of energy
momentum tensor and that of current. As a consequence, the thermal conductivity
and electric conductivity are calculated in terms of the parameters of the
fundamental theory. We find that Wiedermann-Franz law hold with Lorentz number
$1/e^2$
