Our previously published, grid-based compressible electrostatic continuum model [1] includes explicit treatment of electrostriction, a nonlinear dielectric effect. An improved version of this method, which more accurately treats the solvent-solute cavity dielectric boundary, is presented and tested against the model of Wood, Quint and Grolier [2] for the case of a spherical ion in supercritical water atT=653&hthinsp;K.This application illustrates the importance of electrostriction—and thus also of models which explicitly include this effect—for solvation in supercritical water. ©2000 American Institute of Physics.