  We study charged hydrodynamics in a periodic lattice background. Fluctuations
are Bloch waves rather than single momentum Fourier modes. At boundaries of the
unit cell where hydrodynamic fluctuations are formally degenerate with their
Umklapped copy, level repulsion occurs. Novel mode mixings between charge,
sound, and their Umklapped copies appear at finite chemical potential -- both
at zero and finite momentum. We provide explicit examples for an ionic lattice,
i.e. a periodic external chemical potential, and verify our results with
numerical computations in fluid-gravity duality.
