Barley (Hordeum vulgare L.) is considered one of the most valuable cereal crops worldwide, ranking fourth in production and providing high-quality forage for ruminant animals. Conventional forage cultivation is unsustainable in arid and semi-arid regions, where water scarcity and an extreme arid climate prevail, because of the high water requirements. This study aims to assess the potential of using municipal treated wastewater (TWW) as an alternative irrigation source for barley, focusing on its effects on growth, yield, nutritional content, and heavy metal accumulation in different barley genotypes. The results of a 2-year field experiment showed that TWW significantly improved biological yield, grain yield, straw yield, number of spikes, and 1000-grain weight compared to potable water irrigation (PW). Among the barley genotypes, 58 1A consistently exhibited the highest grain yield, harvest index, and 1000-grain weight, while 60 1A produced the highest biological and straw yields along with the most tillers. Under 100%TWW irrigation, the genotype 58 1A exhibited the highest grain yield, producing 4.51 and 5.16 ton ha(-1) in 2022 and 2023, respectively. This represented an increase of 40.64% to 44.20% over the control treatment (PW). Additionally, TWW enhanced photosynthetic pigments, crude proteins, fiber content, and higher levels of essential minerals (N, Mg, K, and P). However, the levels of heavy metals remained within the permissible limits for forage crops. In conclusion, TWW effectively enhances barley growth, yield, and nutritional quality while ensuring safe heavy metal levels, offering a sustainable solution to water scarcity in arid regions. Future research should focus on the long-term effects of TWW on soil health and its impact on other crops, as well as optimizing its treatment for more efficient and sustainable farming.