Soil amendment with superabsorbent (SAP) is an emerging and promising solution to maintain soil humidity in arid and semi-arid areas and improve water use efficiency. This study aims to investigate the impact of a hydrophilic copolymer derived from polyacrylamide and potassium acrylate on soil bulk density, porosity, and plant growth under drought stress. Effect of SAP at various rates (S0.1%, S0.3%, and S0.5% on soil dry weight), was investigated in two soil textures (clayey loam (CLS) and sandy loam (SLS)). Additionally, SAP's effect on tomato growth was assessed under different water regimes corresponding to 75, 50, and 25% of field capacity. Results showed that SAP at 0.5 and 0.3% rates significantly increased the porosity of both soils compared to the untreated control (T0%). Additionally, the bulk density was decreased in both soils with the three rates, S0.5%, S0.3%, and S0.1%, by 56.98, 35.18, and 13.17% in CLS, and by 54.54, 37.37, and 19.29% in SLS, respectively. Moreover, under water stress, the 0.5% rate demonstrated the most pronounced effect, enhancing water productivity, resulting in a significant reduction in irrigation water required by 62.16% in CLS and 30.64% in SLS, with significant enhancements in plant dry weight, root morphology, glycine betaine content, and nitrate reductase activity, relative to corresponding controls. Considering the ability of the superabsorbent treatments 0.5% and 0.3% to enhance soil porosity and water retention while reducing bulk density, the increased water availability in soil improved water productivity, which promoted tomato growth under drought stress.