Climate change represents a pervasive global challenge and serves as a significant constraint on agricultural yields, jeopardizing food production worldwide. Drought stress stands out as one of the primary challenges confronting the agricultural sector. The scarcity of water resources adversely affects various physiological parameters, growth, and overall productivity of plants. The application of folic acid (FA) through foliar treatment may help mitigate the detrimental effects associated with water limitations. The Experimental Station of the National Research Centre, located in the Al-Nubaria District of the El-Behaira Governorate in Egypt, conducted a study to evaluate the impact of foliar application of folic acid at two concentrations (5 and 10 mg/l) on barley plants subjected to three different irrigation levels (100%, 75%, and 50% of water irrigation requirements). The research aimed to assess the interaction of these factors on productivity through various physiological parameters. It was observed that moderate and severe water stress (75% and 50% of WIR) led to significant reductions in yield and its components, as well as adverse effects on physiological traits, including leaf photosynthetic pigments and endogenous Indole acetic acid (IAA). Conversely, there was an increase in certain osmolytes, such as total soluble sugars (TSS), proline, and phenolic compounds. Additionally, the application of folic acid at varying concentrations not only enhanced the yield of barley plants but also alleviated the negative impacts of water stress by improving the physiological parameters studied, including photosynthetic pigments and IAA, along with osmolytes and phenolic content.