This article reports on quantified soil water gains and their possible effects on summer water relationships in a semiarid Stipa tenacissima L. grasslands located in SE Spain. We believe that the net soil water gains detected using minilysimeters could be from soil water vapour adsorption (WVA). Our study of high water-stress showed stomatal conductance (21.8-43.1 mmol H2O m-2 s-1) in S. tenacissima leaves unusual for the summer season, and the evapotranspiration from S. tenacissima grassland, estimated by a multi-source sparse evapotranspiration model, closely corresponding to total WVA. This highlights the importance of summer soil WVA to stomatal conductance and vital transpiration in S. tenacissima. This study measured pre-dawn leaf water potential (ψ) response to sporadic light rainfall, finding that a light summer rainfall (1.59 mm day-1) was sufficient to vary ψ in S. tenacissima from -3.8 (close to the turgour loss point) to -2.7 MPa. We hypothesize that soil WVA can supply vegetation with water vital to its survival in seasons with a severe water deficit, giving rise to a close relationship between soil water dynamics and plant water response. © 2006 Springer Science+Business Media B.V.