Chromatographic theory of competitive solute movement through porous, reactive soils with nonlinear adsorption isotherms is extended to conditions of unsteady flow in the unsaturated zone under gravity. By treating water content as an extra solute component, equations governing coupled movement of solute and water through reactive soils under gravity are shown to be a special case of those governing competitive solute movement, leading to a quantitative description of the coupled movement of the water and solute fronts through a soil column. When one solution displaces another at a different concentration and water potential in a reactive soil, the solute and water front splits up into two distinct subfronts, separated by a region in which both concentration and potential are constant. Each subfront is characterized by a region in which water content and concentration vary in a predetermined manner, according to certain functions (characteristics), one of which must remain constant over each subfront. Only in certain simple cases will solute concentration and water content vary independently of each other. The case when the hydraulic conductivity depends on solute concentration is explicitly considered.