Water scarcity poses severe challenges to rainfed cropping system diversification. The objective was to evaluate how variations in sunn hemp intercropping timing (P) and stand density (D) affect soil water storage (SWS), evapotranspiration (ET), aboveground biomass (AGB) and water productivity (WP) of rainfed maize/sunn hemp intercropping. This was conducted using a split-plot experimental design under in-field rainwater harvesting (IRWH) tillage. The trial had three intercropping times [simultaneously with maize planting (P1), at V15 maize growth stage (P2), and R1 maize growth stage (P3)] plus sole maize (SM) and sole sunn hemp (SSH) as the main plot factors and three stand densities [16 (D1), 32 (D2), and 48 (D3) plants m-2] as the subplot factors, with three replicates for both the 2019/20 and 2020/21 seasons. Results revealed that soil water storage (SWS) was highest at "Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie" (BBCH) 14 under P3D1 (199.80 mm), while P1 and P2 recorded significantly lower values later in the season. Evapotranspiration peaked at BBCH 39, with P1D3 recording the highest value (278.9 mm). Aboveground biomass was greatest under P1D1 across both seasons, although P1D3 maintained superior yield performance despite density increases. Water productivity reached its peak at BBCH 61 with P1D3 achieving 80.8 kg ha-1 mm-1 , followed by SSHD3 at 68.8 kg ha-1 mm-1 . At harvest, P1 consistently recorded the highest WP, with values of 20.21 kg ha-1 mm-1 (P1D1), 30.8 kg ha-1 mm-1 (P1D2), and 29.2 kg ha-1 mm-1 (P1D3). Therefore, the study concluded that intercropping sunn hemp simultaneously with maize at planting and a medium planting of 32.1 plants m-2, are the most effective management strategies to improve crop water productivity in semi-arid regions.