Use of material coordinates often simplifies analysis and offers physical insights into one-dimensional flow in porous media. Their use also ensures that material balance is preserved. This paper identities common elements in material approaches to water flow in saturated swelling systems and to solute movement during non-steady water flow in unsaturated porous materials. It then shows that solute transport during non-steady flow of water in a swelling system can be described in terms of a water-based coordinate system which, in turn, is based on the distribution of the solid. The coordinates are simply defined and measured and their use results, for a non-reactive solute, in a non-linear diffusion equation, solutions of which are available for many practically important initial and boundary conditions. The approach is illustrated using transient profiles involving Na+/Ca2+/Mg2+ measured during constant pressure filtration experiments with bentonite.