Iran, in arid and semi-arid regions, faces a severe water crisis, with wheat production stressing limited water resources. This study used Iran's National Irrigation Water Requirement System (NIAZAB) to evaluate nationwide spatial patterns of wheat water use. First, validation with data from 238 farms across 11 major wheat-producing provinces (2016-2017) showed strong agreement between simulated and observed irrigation, yields and water productivity (d > 0.9), confirming model reliability. In the second phase, analysis across 766 sites in 31 provinces (2014-2024) revealed a mean crop water requirement (ETc) of 512.9 (mm), whereas actual evapotranspiration (ETa) averaged 302.9 (mm), indicating widespread water stress. The mean actual irrigation requirement (IRa) was 202.7 (mm), with water consumption (WRa) showing high spatial variability, especially in the southern and southeastern regions of Iran. The average water productivity (WP) was 0.94 kg m(-3), with a coefficient of variation above 50%, reflecting inefficiencies. Sensitivity analysis identified effective precipitation (Pe) as the main driver of irrigation demand and WP. k-means clustering identified three regional groups with contrasting irrigation pressure and productivity. These results highlight the need for region-specific irrigation and crop management to improve water productivity amid increasing scarcity.