  In this paper we consider weighted $L^2$ integrability for solutions of the
wave equation. For this, we obtain some weighed $L^2$ estimates for the
solutions with weights in Morrey-Campanato classes. Our method is based on a
combination of bilinear interpolation and localization argument which makes use
of Littlewood-Paley theorem and a property of Hardy-Littlewood maximal
functions. We also apply the estimates to the problem of well-posedness for
wave equations with potentials.
